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Evolution and phylogeography of Halimeda section Halimeda (Bryopsidales, Chlorophyta)
Abstract
Nuclear ribosomal and plastid DNA sequences of specimens belonging to section Halimeda of the pantropical green seaweed genus Halimeda show that the group under scrutiny contains many more genetically delineable species than those recognized by classical taxonomy. Discordances between phylograms inferred from nuclear and plastid DNA sequences suggest that reticulate evolution has been involved in speciation within the clade. Nonetheless, our data do not allow ruling out certain alternative explanations for the discordances. Several pseudo-cryptic species are restricted to the margins of the generic distribution range. In a clade of H. cuneata sibling species from widely separated subtropical localities in the Indian Ocean, the South African sibling branches off first, leaving the Arabian and West Australian species as closest relatives. We hypothesize that geographic isolation of the siblings may have taken place following Pleistocene or Pliocene periods of climatic cooling during which subtropical species occupied larger distribution ranges. A more basal separation of Atlantic, Indo-Pacific, and Mediterranean species indicates vicariance. The alternative events that could have caused this vicariance are discussed.
Supplementary resources (6)
Nucleotide Sequence
February 2005
Nucleotide Sequence
February 2005
Nucleotide Sequence
February 2005
Nucleotide Sequence
February 2005
... This makes it an ideal model to investigate genus-level biogeographic history associated with paleobiogeographical and macroecological processes, and to characterize evolutionary niche dynamics in the ocean (Hu et al. 2016). For this reason, it has been the subject of some of the most comprehensive evolutionary studies in the field (Kooistra et al. 2002, Verbruggen et al. 2005, 2009). In the Mediterranean, Halimeda is represented by the native Halimeda tuna (Fig. 1A), widespread throughout the basin (besides the recently introduced Halimeda incrassata, Al os et al. 2016). ...
... (http:// www.geneious.com). The complete data set includes the 84 newly assembled sequences and two sequences previously published by Verbruggen et al. (2005; Table S1). The tufA and rpl2-rpl14 data sets consisted of alignments 822 bp and 1,499 bp long respectively. ...
... The low variation of tufA confirms that in the Mediterranean this alga represents a single, well-defined species; our data do not provide any evidence for the possible existence of cryptic species. It should be noted that beyond our Mediterranean context, the name H. tuna has also been applied in the Caribbean and the Indo-Pacific, but molecular work has shown that these are clearly different species unrelated to the Mediterranean lineage of H. tuna studied here (Verbruggen et al. 2005). The conclusion that within the Mediterranean Sea H. tuna forms a single species should not be considered obvious or banal. ...
Populations of many Mediterranean marine species show a strong phylogeographic structure, but the knowledge available for native seaweeds is limited. We investigated the genetic diversity of the green alga Halimeda tuna based on two plastid markers (tufA gene and a newly developed amplicon spanning 5 ribosomal protein genes and intergenic spacers, the rpl2‐rpl14 region). The tufA sequences showed that Mediterranean H. tuna represents a single, well‐defined species. The rpl2‐rpl14 results highlighted a genetic separation between western and eastern Mediterranean populations: specimens collected from widely scattered locations in the Adriatic/Ionian region shared a haplotype unique to this region, and formed a group separated from all western Mediterranean regions. Specimens from Sardinia also formed a unique haplotype. Within the western Mediterranean basin, a gradual shift in the frequency of haplotypes was apparent along a West‐East gradient. Our results represent the first clear evidence of an East‐West genetic cleavage in a native Mediterranean macroalga and offer an interesting perspective for further research into fine‐scale seaweed population structure in the NW Mediterranean Sea.
... The sections are based on morphological synapomorphies, predominantly the types of fusions that medullary siphons show at nodes. Section Halimeda has 11 recognised morphological species (Verbruggen et al. 2005a), and molecular data have indicated pseudo-cryptic as well as cryptic species often restricted to the margins of the generic distribution range. Verbruggen et al. (2005a) studied the evolution and phylogeography of section Halimeda, of which H. cuneata is a member. ...
... Section Halimeda has 11 recognised morphological species (Verbruggen et al. 2005a), and molecular data have indicated pseudo-cryptic as well as cryptic species often restricted to the margins of the generic distribution range. Verbruggen et al. (2005a) studied the evolution and phylogeography of section Halimeda, of which H. cuneata is a member. Pertinent to our present study is that seven distinct cryptic species were discovered within the single morphospecies H. cuneata, most of them geographically isolated from the others. ...
... The names used in the phylograms for this study are modified on the basis of Verbruggen et al. (2005a) ...
Halimeda J.V.Lamour. is a green algal genus that is an important component of tropical reefs and lagoons. Although it does not generally occur outside the tropics, the range of one putatively widespread species, Halimeda cuneata Hering, in Western Australia extends southward past Cape Leeuwin to its southern extreme at Cape Howe and around to its most easterly record at Middle Island of the Recherche Archipelago. Previous molecular studies have shown that H. cuneata as recorded worldwide encompasses cryptic species diversity, with most of the cryptic entities being geographically isolated from the others. Halimeda cuneata has been the name consistently applied to specimens from the south-western coast of Australia, where it has been regarded as the only representative of its genus in the region. Using a combination of morphological features and assessment of species boundaries based on a plastid gene (tufA) and a nuclear protein-coding gene (HSP90), we have reassessed the supposed presence of H. cuneata in south-Western Australia. Our results showed the existence of two species in the region, namely, H. versatilis J.Agardh, to which the name H. cuneata has been misapplied, and H. gigas W.R.Taylor, a central-Pacific species previously recorded only from tropical Australia.
... 9, pl. 2) and Verbruggen et al. (2005e;HV605, HV632) as H. cuneata f. digitata. This belongs to the H. discoidea tropical Indo-Pacific Ocean clade. ...
... Halimeda unknown 1 (morphotype U) possessed relatively thin cuneate segments and is most closely allied to those of H. discoidea (both Thai-Malay Peninsula samples and entity 1, Verbruggen et al. 2005e), H. cuneata (entity 2; Verbruggen et al. 2005e) and H. cuneata f. digitata (that belongs to H. discoidea; Barton 1901 andVerbruggen et al. 2005e cuneata is known only from the subtropical Indian Ocean (Verbruggen et al. 2005e). ...
... Halimeda unknown 1 (morphotype U) possessed relatively thin cuneate segments and is most closely allied to those of H. discoidea (both Thai-Malay Peninsula samples and entity 1, Verbruggen et al. 2005e), H. cuneata (entity 2; Verbruggen et al. 2005e) and H. cuneata f. digitata (that belongs to H. discoidea; Barton 1901 andVerbruggen et al. 2005e cuneata is known only from the subtropical Indian Ocean (Verbruggen et al. 2005e). ...
The Thai-Malay Peninsula separates the Andaman Sea from the Gulf of Thailand. This barrier is known to affect species distribution and genetic diversity of marine organisms. Biodiversity studies need a correct species taxonomy to interpret their biogeography; this is especially relevant in marine algae where morphological characters are few or cryptic. We address species distributions of the important macroalgal genus Halimeda. The combination of morphological data and chloroplast tufA gene sequences were used to identify species, and to reveal the variation among Halimeda species around the Thai-Malay Peninsula. The morpho-anatomical and molecular analysis showed eight species of Halimeda in Thai and Malaysian waters: Halimeda borneensis, H. discoidea, H. gigas, H. macroloba, H. micronesica, H. minima, H. opuntia, H. renschii, and two undescribed species. Three species, H. minima, H. renschii and H. micronesica, were reported for the first time from the area. Species variation was much greater in the Andaman Sea than in the Gulf of Thailand. Our results show great variation in species composition and genetic variation between the two sides of the peninsula, which could be due to differences in sea-surface currents and environmental differences between the two sides of this important marine barrier.
... However, small deviations did occur. Morphotype G (H. discoidea) is polyphyletic, with widely divergent clades containing Indo-Pacific and Atlantic/Caribbean specimens (see also Kooistra et al. 2002, Verbruggen et al. 2005b, 2009b ). Specimens in morphotype J (H. taenicola) formed a moderately to well-supported clade (82% BP 90%), but was subdivided into two divergent subgroups, one with individuals from French Polynesia and the Maldives, and the second with specimens from Chesterfield. ...
... discoidea 2). The genetic distinctness of Atlantic and Indo-Pacific specimens belonging to the morphospecies has been discussed in detail in the literature (Kooistra et al. 1999, Verbruggen et al. 2005b, 2009b). The polyphyly of H. gracilis initially noted by Kooistra et al. (2002) has later been confirmed with better taxon sampling (Verbruggen et al. 2009b, this study). ...
... Regrettably, we were unable to generate DNA data for these species. However, because these species represent clear-cut morphotypes that have been shown to form distinct DNA clusters (Verbruggen et al. 2005b,c, this study) with no reports of cryptic diversity, a high degree of confidence can be attached to these records. We also identified a DNA cluster (H. ...
Halimeda is a genus of calcified and segmented green macroalgae in the order Bryopsidales. In New Caledonia, the genus is abundant and represents an important part of the reef flora. Previous studies recorded 19 species that were identified using morphological criteria. The aim of this work was to reassess the diversity of the genus in New Caledonia using morpho-anatomical examinations and molecular analyses of the plastid tufA and rbcL genes. Our results suggest the occurrence of 22 species. Three of these are reported for the first time from New Caledonia: Halimeda kanaloana, H. xishaensis, and an entity resembling H. stuposa. DNA analyses revealed that the species H. fragilis exhibits cryptic or pseudocryptic diversity in New Caledonia. We also show less conclusive evidence for cryptic species within H. taenicola
... Although it is known that within the sections Rhipsalis, Micronesicae, Pseudo-opuntia and Opuntia there is a marked conservatism for tropical temperatures, several niche shifts into colder water have been documented within the section Halimeda (Verbruggen et al., 2009). Modern Mediterranean Halimeda tuna (Ellis and Solander) Lamouroux populations for instance occur at sites with seasonal sea surface temperature (SST) minima around 10 • C and the H. discoidea Decaisne population at the coast of Oman is affected by cold upwelling water (Verbruggen et al., 2005(Verbruggen et al., , 2009). The northernmost Halimeda occurrence is that of H. tuna on the Balearic shelves in the Mediterranean Sea (Fornos et al., 1992;Canals and Ballesteros, 1997;Fig. ...
... Based on molecular phylogenetics, it is considered that the invasion of tropical seaweeds such as Halimeda into temperate waters occurred due to global cooling since the late Paleogene (Verbruggen et al., 2009). At this time thermophile algae may have been dispersed during periods of minimal glaciations across low latitudes (Hommersand, 1986;Verbruggen et al., 2005). However, so far no palaeontological findings confirm these hypotheses. ...
... The available palaeobiogeographic data show that Halimeda has not managed the jump into colder water in the Mediterranean region during the Middle Miocene. For the recent Mediterranean H. tuna Verbruggen et al. (2005) assumed that its relatively basal phylogenetic position suggests that it is palaeoendemic from the time when the Mediterranean Sea was formed rather than a recent invader from the Atlantic. This, however, requires assuming that the lineage that give rise to H. tuna survived the Messinian salinity crisis (MSC), during which the Mediterranean Sea almost completely dried up (Verbruggen et al., 2005). ...
The bryopsidalean alga Halimeda gained an important role as carbonate producer in Cenozoic tropical coral reefs and became a significant constituent of the modern Mediterranean seaweed flora. There are, however, open questions at which time the thermophile alga appeared in the cooler Mediterranean Sea and why it is not detected in coral reefs of the modern Persian Gulf. To unravel the biogeography and ecology of Halimeda at its northern margin of distribution, we use fossil Halimeda records of the Central Paratethys/Medditerranean for comparison of the geological, (palaeo)ecological and evolutionary dispersal constraints of the alga in the Miocene and Holocene Persian Gulf. The revealed spatial and temporal distribution patterns of Halimeda in the regions of the Mediterranean and Arabian seas identify water temperature as the major ecological constraint and the extreme Plio-Pleistocene climate changes as the motor for the dispersal and evolution of Halimeda in higher latitudes. Generally, the distribution of tropical species in higher latitudes was related to warm climate intervals during the Neogene. Accordingly, the available (palaeo)biogeographic data implies that the warm-adapted ancestors of the present-day Mediterranean H. tuna population possibly entered the Mediterranean Sea during the mid-Pliocene global warmth and became isolated during subsequent cooling. It also implies that the warm Persian Gulf water is probably unsuitable for the cool-adapted H. discoidea population in the Gulf of Oman and that its tropical ancestors could have reached the Gulf of Oman only during a Pleistocene glacial phase when monsoon-induced upwelling of cold water in the Arabian Sea was reduced and the Persian Gulf fell dry. This example demonstrates the limitation of the actualistic palaeontological approach when using biota at the edges of their distribution range as palaeoclimate proxy.
... region of ingroup taxa, as well as Halimeda discoidea Decaisne, H. micronesica, H. gracilis and H. opuntia as close outgroup taxa and Udotea flabellum (Ellis & Solander) Howe, Penicillus capitatus Lamarck and Flabellia petiolata (Turra) Nizamuddin as more distant outgroups were downloaded from GenBank (accession numbers listed in Appendix). Partial tufA and rpl5–rps8–infA sequences were aligned with ClustalW 1.82 as described in Verbruggen et al. (2005b). The tufA and rpl5–rps8– infA sequence data sets were concatenated before analysis. ...
... The clear-cut separation of Atlantic and Indo- Pacific species in the phylograms suggests separate diversification of Halimeda section Rhipsalis in the ocean basins. Previous research has shown basal or near-basal separation of Indo-Pacific and Atlantic species of all five sections of Halimeda (Kooistra et al., 2002; Verbruggen & Kooistra, 2004; Verbruggen et al., 2005b). This suggests that a vicariance event allowed independent diversification of the different sections in the Caribbean Sea and Indo-Pacific ocean basin (Kooistra et al., 1999Kooistra et al., , 2002). ...
... This pattern is common in marine taxa of Tethyan origin, from parrotfishes (Streelman et al., 2002) to mangrove trees (Ellison et al., 1999). Closure of the Tethyan Seaway in the Middle East during the Miocene and the rise of the Central American Isthmus in the Pliocene are hypothesized vicariance events for Halimeda (Kooistra et al., 1999Kooistra et al., , 2002 Verbruggen et al., 2005b). The plastid and nuclear phylograms (Figs 1, 2) exhibit a sister relationship between H. kanaloana and H. heteromorpha, although this relationship has only moderate bootstrap support in the cpDNA data set. ...
The tropical green algal genus Halimeda is one of the best studied examples of pseudo-cryptic diversity within the algae. Previous molecular and morphometric studies revealed that within Halimeda section Rhipsalis, Halimeda incrassata included three pseudo-cryptic entities and that the morphological boundaries between H. incrassata and Halimeda melanesica were ill-defined. In this paper, the taxonomy of H. incrassata is revised: two pseudo-cryptic entities are described as new species, Halimeda kanaloana and Halimed heteromorpha, while H. incrassata is redefined to encompass a single, monophyletic entity. Similarities and differences between the three species and H. melanesica are discussed. Monophyly of H. heteromorpha, which was questioned in a former study, is reinvestigated using sets of 32 ITS1–ITS2 and 21 plastid rps3 sequences and various alignment and inference methods. The phylogenetic relationships within Halimeda section Rhipsalis are inferred from nuclear 18S–ITS1–5.8S–ITS2 and concatenated plastid sequences (tufA & rpl5–rps8–infA) and interpreted in a biogeographic context.
... A limited number of molecular-assisted alpha-taxonomic studies have been conducted in French Polynesia, encompassing the Rhodophyta (Gelidiales [54], Gibsmithia [55], Asparagopsis [56], Grateloupia filicina [57,58], Corallinophycidae [59][60][61][62], Laurencieae [63]), Chlorophyta (Halimeda [64][65][66][67][68]), Ochrophyta (Dictyota [69][70][71][72], Lobophora [13,73], Newhousia [21], Sargassum [74], Turbinaria [75]), and Cyanobacteria [20], but nothing on seagrasses. These molecular-based studies generated over 500 sequences, but from a limited number of taxa, and a bulk from the genus Lobophora (>350 sequences [13]), followed by Halimeda (>90 sequences [64][65][66][67]76]), Sargassum (>30 sequences [74]), and Newhousia (20 sequences [21]). ...
... A limited number of molecular-assisted alpha-taxonomic studies have been conducted in French Polynesia, encompassing the Rhodophyta (Gelidiales [54], Gibsmithia [55], Asparagopsis [56], Grateloupia filicina [57,58], Corallinophycidae [59][60][61][62], Laurencieae [63]), Chlorophyta (Halimeda [64][65][66][67][68]), Ochrophyta (Dictyota [69][70][71][72], Lobophora [13,73], Newhousia [21], Sargassum [74], Turbinaria [75]), and Cyanobacteria [20], but nothing on seagrasses. These molecular-based studies generated over 500 sequences, but from a limited number of taxa, and a bulk from the genus Lobophora (>350 sequences [13]), followed by Halimeda (>90 sequences [64][65][66][67]76]), Sargassum (>30 sequences [74]), and Newhousia (20 sequences [21]). These studies included several markers, encompassing cox1, cox2-cox3 intergeneric spacer, cox3, nad1, psbA, psaA, rbcL, tuf A, ITS, 16S, 18S, 28S, 23S, 26S. ...
Located in the heart of the South Pacific Ocean, the French Polynesian islands represent a remarkable setting for biological colonization and diversification, because of their isolation. Our knowledge of this region’s biodiversity is nevertheless still incomplete for many groups of organisms. In the late 1990s and 2000s, a series of publications provided the first checklists of French Polynesian marine algae, including the Chlorophyta, Rhodophyta, Ochrophyta, and Cyanobacteria, established mostly on traditional morphology-based taxonomy. We initiated a project to systematically DNA barcode the marine flora of French Polynesia. Based on a large collection of ~2452 specimens, made between 2014 and 2023, across the five French Polynesian archipelagos, we re-assessed the marine floral species diversity (Alismatales, Cyanobacteria, Rhodophyta, Ochrophyta, Chlorophyta) using DNA barcoding in concert with morphology-based classification. We provide here a major revision of French Polynesian marine flora, with an updated listing of 702 species including 119 Chlorophyta, 169 Cyanobacteria, 92 Ochrophyta, 320 Rhodophyta, and 2 seagrass species—nearly a two-fold increase from previous estimates. This study significantly improves our knowledge of French Polynesian marine diversity and provides a valuable DNA barcode reference library for identification purposes and future taxonomic and conservation studies. A significant part of the diversity uncovered from French Polynesia corresponds to unidentified lineages, which will require careful future taxonomic investigation.
... Thus, the shape of smaller mature segments was consistently different from that of relatively larger segments. Mediterranean H. tuna is characterized by its bean-shaped or broadly oval segments [1,57]. According to our analyses, these shapes correspond to the larger segments in both populations. ...
... It should be noted that H. tuna plants inhabiting the northern-most area of the species distribution in the Northern Adriatic are relatively very small and composed by fewer segments than their counterparts from the central Mediterranean or tropical regions [1,57,64]. Therefore, should more asymmetric segments be expected in Northern Adriatic plants than in H. tuna from the core regions of the distribution area? Increased FA and total asymmetry were reported in marginal populations of several animal model systems [62,65] and may reflect borderline environmental conditions at the margins of the distribution area. ...
Green algae of the genus Halimeda have modular siphonous thalli composed of multiple repeated segments. Morphological variation among the segments has been related to various environmental factors, which often jointly affect their size and shape. The segments are bilaterally symmetric, which means that their shape variation can be decomposed into the symmetric and asymmetric components. Asymmetric variation might reflect both environmental heterogeneity and developmental instability of morphogenetic processes during the development of segments. In the present study, we examined if segment shape in H. tuna is related to their size and if an allometric relationship can also be found with respect to their asymmetry. Relative contributions of directional and fluctuating asymmetry to the segment shape variation within individual plants were investigated at two close localities in the northern Adriatic Sea. A series of equidistant semilandmarks were set along the outline of the segments, and analyzed by geometric morphometrics using two parallel methods to optimize their final position. Symmetric variation was strongly constrained by allometry, which also explained differences between populations. Smaller segments were significantly more asymmetric, but the difference in asymmetry between populations could not be explained solely by this allometric relationship. These differences between populations might have been caused by variation in local environmental factors. We conclude that members of the genus Halimeda represent an intriguing model system for studies of morphometric symmetry and asymmetry of sessile marine organisms, including effects of allometric relationships and infraspecific variation in relation to environmental factors of the benthic coastal habitats.
... Halimeda in tropical and warm-temperate marine environments (e.g. Hillis-Colinvaux, 1980;Verbruggen, Clerck, Schils, Kooistra, & Coppejans, 2005) is remarkably similar to that of Zeapora during the late Emsian and early Eifelian. Water temperature has been identified as major ecological constraint for the dispersal and evolution of the thermophile alga (Reuter, Piller, & Richoz, 2012;Verbruggen et al., 2009). ...
... Its worldwide spreading therefore occurred prior to the isolation of large low-latitude oceanic regions during the Neogene, which resulted from the restriction or closure of a series of marine gateways located at low latitudes (i.e. Tethyan Seaway, Panama Isthmus, restricted throughflow in southeastern Asia) in concert with a narrowing of the tropical climatic belt due to long-term global cooling (Hillis, 2001;Reuter et al., 2012;Verbruggen et al., 2005). Likewise, the Early to Middle Devonian climate and the land-sea configuration provided good conditions for a circum-tropical dispersal of Zeapora. ...
en The taxonomy of Zeapora Penecke, 1894 has a long but inconsistent taxonomic history. Originally identified as cyclostomate bryozoan, it was later assigned to the trepostomate bryozoans, amphiporid stromatoporoids, thamnoporid tabulate corals and dasycladacean algae before it was finally classified as Halimedaceae or Udoteaceae. Based on newly collected material from the type locality in the Graz Paleozoic (Eastern Alps, Austria) the taxonomic description of the type species Z. gracilis is emended and the udoteacean genus Litanaella Schuysky & Schirschova, 1987 is placed in synonymy with Zeapora. Following this opinion, Zeapora remains no longer endemic in the alpine Noric Terrane but shows a peculiar circum‐tropical distribution during the Early to Middle Devonian similar to modern Halimeda.
Abstract
ja Zeapora 属(Penecke, 1894) の分類は長い歴史を有するが，その内容は一貫性を欠いている.当初，同属は円口目のコケムシとして記載され，その後，コケムシ，層孔虫，床板サンゴ，カサノリ類の藻類とみなされ，最終的にはサボテングサ科もしくはハゴロモ科の藻類として分類されるに至った．Zeapora 属の模式種である Z. gracilis の模式標本が採取されたオーストリア，グラーツ地域の古生界(東アルプス山脈)から新たに得られた標本に基づき，同種の分類を見直した．その結果， Zeapora属とLitanaella属(Schuysky & Schirschova, 1987)とは同物異名であることが判明した．これにより，Zeapora属はアルプス山脈のNoric Terraneに特有のものではなく，前期〜中期デボン紀には，現生サボテングサ属のように，熱帯域に広く分布していたことが明らかとなった.
... cuneata, including a sequence previously published as H. cuneata from Brazil (AY826358), were phylogenetically distinct from well-supported clades of H. cuneata from other parts of the world. The type locality of H. cuneata is South Africa, from which two species-level clusters corresponding to the morphology of H. cuneata are known (Verbruggen et al. 2005a). The intraspecific variation of Brazilian H. aff. ...
... In Halimeda section Halimeda, H. tuna, H. discoidea and H. cuneata are overall morphologically consistent with the descriptions given by Hillis-Conlivaux (1980) and Bandeira-Pedrosa et al. (2004a, b Verbruggen et al. (2005a) and Dijoux et al. (2012) previously reported similar results where each of these morphospecies was recovered as multiple distinct clades, indicating cryptic diversity. Many of these cryptic species are geographically separated from one another, and each of the sections in Halimeda shows a biogeographic separation between Indo-Pacific and Atlantic sublineages, suggesting that vicariance may have happened either across the Isthmus of Panama (Kooistra et al. 1999) or, as molecular clocks would suggest, across the Middle Eastern Isthmus (Verbruggen et al. 2009a, b (Fig. 9) with 9.4%-9.5% of divergence regarding our H. jolyana. ...
The genus Halimeda has a wide geographic distribution in tropical to subtropical regions of the world.
Molecular studies have uncovered cryptic and pseudocryptic species as well as strong biogeographic signals in
phylogenies. To date, the diversity of Brazilian Bryopsidales has been studied from only a morphological perspective.
Here we revised the diversity of Brazilian Halimeda based on molecular data (DNA barcode assessments of the tufA
marker and multigene concatenated phylogenies) as well as morphological observations. Of the seven recognized
morphospecies, only three were confirmed by molecular data: Halimeda opuntia, H. simulans and H. incrassata. The
remaining four species, referred to as H. aff. cuneata, H. aff. gracilis, H. aff. tuna and H. aff. discoidea, showed
morphological similarities with known species, but their sequences did not group with sequences of specimens from type
localities, indicating the presence of cryptic diversity. Among the four taxa, H. aff. cuneata is so far endemic to Brazil and
is herein described as a new species, H. jolyana sp. nov. The remaining three (pseudo-)cryptic species require further
studies using a global sampling design. The evolutionary and biogeographic origins of Brazilian Halimeda species are
discussed based on new molecular phylogenetic hypotheses.
... cuneata, including a sequence previously published as H. cuneata from Brazil (AY826358), were phylogenetically distinct from well-supported clades of H. cuneata from other parts of the world. The type locality of H. cuneata is South Africa, from which two species-level clusters corresponding to the morphology of H. cuneata are known (Verbruggen et al. 2005a). The intraspecific variation of Brazilian H. aff. ...
... In Halimeda section Halimeda, H. tuna, H. discoidea and H. cuneata are overall morphologically consistent with the descriptions given by Hillis-Conlivaux (1980) and Bandeira-Pedrosa et al. (2004a, b Verbruggen et al. (2005a) and Dijoux et al. (2012) previously reported similar results where each of these morphospecies was recovered as multiple distinct clades, indicating cryptic diversity. Many of these cryptic species are geographically separated from one another, and each of the sections in Halimeda shows a biogeographic separation between Indo-Pacific and Atlantic sublineages, suggesting that vicariance may have happened either across the Isthmus of Panama (Kooistra et al. 1999) or, as molecular clocks would suggest, across the Middle Eastern Isthmus (Verbruggen et al. 2009a, b (Fig. 9) with 9.4%-9.5% of divergence regarding our H. jolyana. ...
The genus Halimeda has a wide geographic distribution in tropical to subtropical regions of the world. Molecular studies have uncovered cryptic and pseudocryptic species as well as strong biogeographic signals in phylogenies. To date, the diversity of Brazilian Bryopsidales has been studied from only a morphological perspective. Here we revised the diversity of Brazilian Halimeda based on molecular data (DNA barcode assessments of the tufA marker and multigene concatenated phylogenies) as well as morphological observations. Of the seven recognized morphospecies, only three were confirmed by molecular data: Halimeda opuntia, H. simulans and H. incrassata. The remaining four species, referred to as H. aff. cuneata, H. aff. gracilis, H. aff. tuna and H. aff. discoidea, showed morphological similarities with known species, but their sequences did not group with sequences of specimens from type localities, indicating the presence of cryptic diversity. Among the four taxa, H. aff. cuneata is so far endemic to Brazil and is herein described as a new species, H. jolyana sp. nov. The remaining three (pseudo-)cryptic species require further studies using a global sampling design. The evolutionary and biogeographic origins of Brazilian Halimeda species are discussed based on new molecular phylogenetic hypotheses.
... This criterion has also been successfully employed by many recent studies (e. g. Noble et al., 2010; Pettengill and Neel, 2011; Reeves and Richards, 2011; Verbruggen et al., 2005) and was adopted in the present study. The hypothesis was that the three previously proposed varieties within P. dilatata would actually form three species. ...
... Among other examples that used the GCC to test species hypotheses (e. g. Noble et al., 2010; Pettengill and Neel, 2011; Reeves and Richards, 2011; Verbruggen et al., 2005), some are analogous to the present study. For example, in a study (e. ...
Documenting biodiversity, at and below the species level, is a persistently challenging task for biologists. Poor understanding of biodiversity may lead to incorrect interpretations of observed variation. The underlying basis of variation can be understood by quantifying multiple sources of information. Nine morphometric characters and plastid DNA sequences (2511 bps) were quantified in a highly variable orchid species, Platanthera dilatata, to evaluate taxonomy of the three named varieties and to understand patterns of evolution. Three morphological groups, identified in a cluster analysis, were distinct in multiple floral traits. Additionally, the three clusters were consistently genetically divergent as indicated by infrequent haplotype sharing, significantly different haplotype frequencies, and significant values of the genealogical sorting index. This level of genetic divergence suggests three species rather than varieties in this complex. The divergent floral morphologies suggest that pollinator-mediated selection may be a driving factor for speciation in this complex.
... Aside from the large body of morpho-taxonomical work, including monographs by Barton (1901), Taylor (1950), Hillis (1959), Hillis-Colinvaux (1980) and Noble (1987), the taxonomy and evolution of the genus have been studied extensively using molecular methods (e.g. Hillis et al. 1998; Kooistra et al. 2002; Kooistra & Verbruggen 2005; Verbruggen et al. 2005a ) and combinations of morphometric and molecular work (Verbruggen et al. 2005bVerbruggen et al. , c, d, 2006). The main conclusion from these last studies is that species diversity has been severely underestimated by morpho-taxonomic methods alone, primarily because of the existence of pairs of very similar species, which have originated largely independently in the Caribbean and Indo-Pacific basins. ...
... Measurements were made only on segments from central thallus parts (Verbruggen et al. 2005c). Specimens appropriately preserved for DNA analysis were extracted, polymerase chain reaction (PCR) amplified and sequenced as described in Verbruggen et al. (2005a). For this study, we focused our efforts on the plastid tufA marker. ...
Halimeda pygmaea and Halimeda pumila, two diminutive calcified green algal species, are described from material collected on Fijian and Bahamian reef slopes, respectively. The species resemble Halimeda cryptica in having a single siphon traversing the nodes between subsequent calcified segments and living in sheltered fore-reef slope habitats. They differ from H. cryptica by their diminutive size and various anatomical features. Molecular sequence data (tyfA) underpin the identity of H. pygmaea and reveal its phylogenetic position as a sister taxon to H. cryptica in the Halimeda section Micronesicae.
... Historical biogeographical insights have shown a strong divide of the main Halimeda lineages (the taxonomic sections of the genus; Verbruggen & Kooistra, 2004) into Atlantic and Indo-Pacific subclades (Kooistra et al., 2002;Verbruggen et al., 2005a;Verbruggen et al., 2009). The sequences of the introduced Mediterranean species clearly correspond to H. incrassata, which is closely related to H. simulans M.Howe and H. monile (J.Ellis & Solander) J.V.Lamouroux, two species that are also restricted to the Atlantic Ocean based on molecular evidence. ...
Not applicable. This is a comment on a recently published study.
... Particularly in the KE-6 population, there was a sole population with a mixed distribution of three lineages. Furthermore, three individuals in the KE-6 population showed an exceptional trend: their GBS-seq belonged to lineage 1 or lineage 3, but their COI sequences were all grouped into lineage 2. Such topological inconsistency had been found in other species, such as the Japanese mantis shrimp Oratosquilla oratoria (Cheng & Sha, 2017) and the pantropical green seaweed genus Halimeda (Verbruggen et al., 2005). ...
Abstract Macrobenthic invertebrates are ubiquitously distributed in the epipelagic zone of the open ocean. Yet, our understanding of their genetic structure patterns remains poorly understood. Investigating the genetic differentiation patterns of pelagic Lepas anatifera and clarifying the potential roles of temperature maintaining this pattern are crucial for our understanding of the distribution and biodiversity of pelagic macrobenthos. In the present study, mitochondrial cytochrome oxidase subunit I (mtDNA COI) from three South China Sea (SCS) populations and six Kuroshio Extension (KE) region populations of L. anatifera sampled from fixed buoys and genome‐wide SNPs from a subset of populations (two SCS populations and four KE region populations) were sequenced and analyzed for investigating the genetic pattern of the pelagic barnacle. Water temperature was different among sampling sites; in other words, the water temperature decreased with latitude increases, and the water temperature on the surface was higher than in the subsurface. Our result showed that three lineages with clear genetic differentiation were found in different geographical locations and depths based on mtDNA COI, all SNPs, neutral SNPs, and outlier SNPs. Lineage 1 and lineage 2 were dominant in the subsurface populations and surface populations from the KE region, respectively. Lineage 3 was dominant in the SCS populations. Historical events during the Pliocene epoch shaped the differentiation of the three lineages, while, nowadays, temperature heterogeneity maintains the current genetic pattern of L. anatifera in the northwest Pacific. The subsurface populations were genetically isolated from the surface populations in the Kuroshio Extension (KE) region, implying small‐scale vertical thermal heterogeneity was also an important factor maintaining the genetic differentiation pattern of the pelagic species.
... Conversely, for a few other species (e.g., Rhipidodesmis caespitosa, Tydemania expeditionis, Chlorodesmis fastigiata), wide ranges have been identified or confirmed, highlighting long-distance dispersal capacity in some species. Large differences in geographical ranges between species is commonly seen in bryopsidalean genera, such as Caulerpa (Belton et al., 2019), Halimeda (Verbruggen et al., 2005), Codium (Verbruggen et al., 2007) and Bryopsis (Hollands et al., 2013). ...
There is a growing interest in elucidating the biogeographical processes underlying biodiversity patterns of seaweeds, with recent studies largely focusing on red and brown macroalgae. This study focuses on the siphonous green algal family Udoteaceae, which is diverse and globally distributed in tropical to warm-temperate seas, and includes species that form important components of tropical reefs. We explored the historical processes that have shaped current biodiversity patterns in the family by analyzing a comprehensive dataset of 568 specimens sampled across its geographical range, and including 45 species, corresponding to 59% of the known diversity. Historical biogeographical analysis was based on a three-locus time-calibrated phylogeny, and probabilistic modeling of geographical range evolution. Many species were found to have restricted ranges, indicative of low dispersal capacity. Our analysis points toward a Western Tethys origin and early diversification of the Udoteaceae in the Triassic period. Three centers of diversity were identified, which are, in order of highest species richness, the Central Indo-Pacific, the Western Indian Ocean, and the Greater Caribbean. Different drivers have likely played a role in shaping these diversity centres. Species richness in the Central Indo-Pacific likely resulted from speciation within the region, as well as recolonization from neighbouring regions, and overlap of some wider ranged species, corroborating the “biodiversity feedback” model. Species richness in the Western Indian Ocean can be explained by ancient and more recent diversification within the region, and dispersal from the Central Indo-Pacific. The Greater Caribbean region was colonized more recently, followed by diversification within the region.
... In addition, a small quantity of micrite could derive from mechanical abrasion and biological erosion of carbonate grains as well as source from direct precipitation from seawater or porewater with or without the aid of microbial activities (Munnecke and Samtleben, 1996). In late Paleozoic, calcified algae were rare or had not yet evolved (Verbruggen et al., 2005). Accordingly, micrite might have been mainly produced by micritization of pre-existing carbonate grains (e.g., fossil skeletons), and inorganic precipitation from seawater/porewater, or induced precipitation by calcified microbes (Kazmierczak et al., 1996;Riding, 1991). ...
The marine magnesium (Mg) cycle is the nexus bridging continent, ocean, and Earth's interior. River water is the only major Mg source, while carbonate precipitation and hydrothermal reaction are the two major processes removing seawater Mg from the ocean inventory. Reconstruction of the deep time marine Mg cycle can be approached with Mg isotopic composition of seawater (δ²⁶Mgsw), because variation of δ²⁶Mgsw may reflect the change of riverine input, carbonate precipitation or intensity of hydrothermal reaction. As the most common component of marine carbonate rocks, micrite or lime mud has been regarded as the premium material that records ancient seawater geochemical compositions and accordingly has been widely used in paleoenvironment studies. However, it is unclear whether micrite can be applied to reconstruct ancient δ²⁶Mgsw. Because of the long residence time of seawater Mg, if micrite archives δ²⁶Mgsw, it is predicted that δ²⁶Mgmicrite should show limited temporal and spatial variation in a short (<1 million years) time scale. In this study, we measured δ²⁶Mg of micrite component (δ²⁶Mgmicrite) collected from Upper Paleozoic limestones in South China. Though δ²⁶Mgmicrite values have limited spatial variation from the time equivalent sections, which suggests a homogeneous ancient seawater Mg isotopic composition, δ²⁶Mgmicrite values show significant stratigraphic variations in all the studied sections. To further test whether such isotopic variations could reflect the change of δ²⁶Mgsw, on the basis of high-resolution conodont biostratigraphic frameworks, we developed a mass balance model to quantify the marine Mg cycle. The modeling results indicate that the observed stratigraphic variations in δ²⁶Mgmicrite cannot be explained by the fluctuation of δ²⁶Mgsw, suggesting that extracting δ²⁶Mgsw signal from micrite is highly complicated. Such complexity might be ascribed to: (1) multiple sources of micrite (micritization of carbonate, direct precipitation from seawater/porewater, and fragmentation of calcified algae), (2) wide ranges of Mg isotopic fractionation in carbonate precipitation (e.g., the vital effect of biogenic Ca‑carbonate precipitation), and (3) post-depositional overprinting at low Mg concentration in micrite. The findings of this study highlight the caution against simple interpretation of stratigraphic variability in δ²⁶Mgmicrite as reflection the evolution of seawater Mg isotopic composition.
... Such a hypothesis could be tested by a detailed analysis of CaCO 3 gradients within segments; preferably those with relatively large size, as our analyses showed that the within-segment utricle size gradient was considerably more pronounced in relatively large segments. These segments usually have discoid to reniform shapes, which are considered "typical" for Mediterranean H. tuna [1,2,38]. Conversely, the analyses showed that smaller segments with shapes considered deviant from the species-specific template that more often occur in lower portions of Halimeda thalli [7] had a considerably less pronounced gradient in surface utricle area. ...
Calcifying marine green algae of genus Halimeda have siphonous thalli composed of repeated segments. Their outer surface is formed by laterally appressed peripheral utricles which often form a honeycomb structure, typically with varying degrees of asymmetry in the individual polygons. This study is focused on a morphometric analysis of the size and symmetry of these polygons in Mediterranean H. tuna. Asymmetry of surface utricles is studied using a continuous symmetry measure quantifying the deviation of polygons from perfect symmetry. In addition, the segment shapes are also captured by geometric morphometrics and compared to the utricle parameters. The area of surface utricles is proved to be strongly related to their position on segments, where utricles near the segment bases are considerably smaller than those located near the apical and lateral margins. Interestingly, this gradient is most pronounced in relatively large reniform segments. The polygons are most symmetric in the central parts of segments, with asymmetry uniformly increasing towards the segment margins. Mean utricle asymmetry is found to be unrelated to segment shapes. Systematic differences in utricle size across different positions might be related to morphogenetic patterns of segment development, and may also indicate possible small-scale variations in CaCO3 content within segments.
... Molecular markers have been globally useful for algal species delimitation (Saunders 2005, Saunders and Kucera 2010, Oliveira-Carvalho et al. 2012), and many studies have shown cryptic diversity among some Halimeda species (Kooistra et al. 1999, Verbruggen et al. 2005b, 2006, Dijoux et al. 2012, Ximenes et al. 2017. ...
Updates on Section Pseudo-opuntia of Halimeda: phylogenetic analyses of H. soniae sp. nov. (Bryopsidales, Chlorophyta) along the Brazilian coast https://doi. Abstract: Halimeda is a genus of green seaweed showing high morphological plasticity. Studies using molecular markers for species delimitations and phylogenetics have revealed cryptic diversity and new species throughout the world. Seven species of Halimeda are currently recognized in Brazil. The present study describes the new species Hal-imeda soniae Ximenes, Oliveira-Carvalho, M. E. Bandeira-Pedrosa et Cassano sp. nov. to accommodate the taxon previously identified as Halimeda aff. gracilis for Brazil. Samples of H. soniae were collected in Espírito Santo State (southeastern Brazil), and plastid gene sequences of tufA and rbcL were obtained. Phylogenetic analyses showed that H. soniae belongs to Section Pseudo-opuntia, together with Halimeda gracilis and Halimeda lacrimosa; the three species have overlapping morpho-anatomical features. Phylogenetic analyses suggest that H. gracilis is restricted to the Indo-Pacific Ocean, whereas the other two species appear to be restricted to the Atlantic. Additional research on Caribbean specimens will be necessary to resolve the taxonomic position of the taxa named as H. lacrimosa and H. gracilis in that region. Based on our results, H. gracilis does not occur in the Brazilian marine flora.
... This could reflect seasonal acclimation (see above) or suggest that there may be population variation in thermal limits (e.g., genetic adaptation) within each of these species.Considering that H. tuna is a thermophilic species, it has been shown that the evolutionary niche dynamics of the Mediterranean population differ considerably from other populations and other species of the Halimeda genus, allowing to inhabit areas with temperatures as low as 10°C(Verbruggen et al., 2009). Phylogenetic studies demonstrate that populations of H. tuna from the Mediterranean Sea are "paleo-endemic" and not recent invaders from the Atlantic Ocean(Verbruggen, De Clerck, Schils, Kooistra, & Coppejans, 2005), which allowed this evolutionary distinction between other conspecific populations to take place. Evolutionary niche dynamics have not been examined for P. oceanica, but studies on the genetic structure of P. oceanica suggest a clear distinction of populations between western and eastern Mediterranean Sea(Chefaoui, Duarte, & Serrão, 2017), which may influence the thermal niche of these populations. ...
The Mediterranean Sea is warming at three times the rate of the global ocean raising concerns about the vulnerability of marine organisms to climate change. Macrophytes play a key role in coastal ecosystems, therefore predicting how warming will affect these key species is critical to understand the effects of climate change on Mediterranean coastal ecosystems. We measured the physiological performance of six dominant native Mediterranean macrophytes under ten temperature treatments ranging from 12 to 34°C to examine their thermal niche, and vulnerability to projected warming in the western Mediterranean up until 2100. Among the macrophytes tested, Cymodocea nodosa was the species with the highest thermal optima and it was beyond current summer temperature. Therefore, C. nodosa may benefit from projected warming over the coming century. The optimal temperature for growth of the other species (Posidonia oceanica, Cystoseira compressa, Padina pavonica, Caulerpa prolifera, and Halimeda tuna) was lower. Similarly, the species presented different upper lethal limits, spanning at least across 5.1°C between 28.9°C (P. oceanica) and >34°C (C. nodosa). Our results demonstrate the variable physiological responses of species within the same local community to temperature changes and highlight important potential differences in climate change vulnerability, among species within coastal marine ecosystems.
... Furthermore, warming of the Mediterranean Sea ) may be also likely contributing to the successful spread of this and other introduced tropical species (e.g., Sampeiro-Ramos et al. 2015;Vergés et al. 2014a). Halimeda incrassata seabeds are one of the most important producers of organic matter and CaCO 3 of tropical areas, generating sediment and also creating structured habitat for many organisms (Verbruggen et al. 2005;Wefer 1980). Importantly, by successfully spreading on sandy bottoms, non-native beds of H. incrassata are adding a novel biogenic structure that likely triggers unknown changes in ecosystem structure. ...
The establishment of non-native habitat-forming seaweeds into new areas may trigger important changes in ecosystem functioning, yet their community and ecosystem-level effects remain largely understudied. Here we studied the spatial distribution of two common fish species (Xyrichtys novacula and Bothus podas) which are key components of communities in unconsolidated bottoms of temperate areas regarding the colonization of the newly-introduced tropical seaweed Halimeda incrassata in the Mediterranean Sea. We used a spatially-explicit before-after-control-impact model and a unique data-set formed by 6 years of fine-scale spatial information of fish and seaweed distribution and abundance. We demonstrate a long-term alteration on the spatial distribution of X. novacula characterized by a shift towards non-native H. incrassata beds, while no effect on B. podas. The introduction of the tropical seaweed H. incrassata has led to the re-distribution of X. novacula, potentially by harbouring a greater biodiversity of species at the base of the food-web through adding biogenic structure to an otherwise bare sediment. Our work demonstrates that non-native tropical habitat-forming species have the potential to maintain or even enhance fish abundance in unconsolidated bottoms in temperate areas potentially altering the functioning of native habitats.
... Setiap kuadran determinasi dan hitung jumlah individu setiap spesies makroalga. Sampel yang telah terkumpul di bawa ke laboratorium Perikanan dan Ilmu Kelautan FPIK Universitas Negeri Papua kemudian dikelompokkan ke dalam masing-masing divisi (Chlorophyta, Rhodophyta dan Phaeophyta) untuk proses identifikasi mengacu pada literatur menurut William & Hunt (1979); Teo & Wee (1983); Bold & Wyne (1985); Chapman & Chapman (1990); Lewmanomont & Ogawa (1995); Atmadja et al. (1996); Silva et al. (1996); Calumpong & Menez (1997); Trono (1997);Verbruggen et al. (2005);Coppejans et al. (2009);Bhavanath et al. (2009);Verbruggen et al. (2009); Eem (2010); Krupek & Branco (2012); Guiry & Guiry (2014). ...
p>Makroalga di daerah Manokwari memiliki keanekaragaman spesis yang tinggi, namun organisme ini sangat rentan terhadap perubahan kondisi lingkungan baik alami maupun tekanan antropogenik. Tujuan penelitian ini adalah mengkaji
komposisi spesies makroalga (klasifikasi dan identifikasi) dan menganalisis struktur komunitas makroalga di perairan intertidal Manokwari Papua Barat. Penelitian pengambilan data di lapangan pada bulan Juni 2014 sampai September 2014 (periode musim timur) pada 2 daerah penelitian yaitu mainland dan outland. Komposisi spesies makroalga ditemukan 28 spesies yang diklasifikasikan ke dalam 3 divisi, 3 kelas, 11 ordo, 16 famili, dan 19 genus. Spesies alga yang di temukan tersebut dikelompokkan dalam 3 divisi utama yaitu alga hijau (Chlorophyta) 14 spesies, alga merah (Rhodophyta) 8 spesies dan alga coklat (Phaeophyta) 6 spesies. Total rata-rata kepadatan jenis makroalga daerah outland lebih tinggi dibandingkan dengan mainland. Analisis struktur komunitas makroalga daerah outland lokasi Mansinam dan Lemon memiliki indeks keanekaragaman lebih tinggi di bandingkan dengan daerah mainland lokasi Rendani, Pasir Putih dan Arfai. Indeks keseragaman pada 5 lokasi penelitian daerah mainland dan outland mendekati 1 dimana populasi individu makroalga tiap jenis menyebar merata dan tidak ada makroalga yang dominan, sedangkan indeks dominansi mendekati nol dimana komunitas makroalga penyusunnya berada dalam keadaan stabil.
Kata kunci: analisis struktur komunitas, klasifikasi, Manokwari, spesies makroalga</p
... In addition, small amounts of micrite derive from mechanical abrasion and biological erosion of carbonate grains as well as from direct precipitation from seawater with or without the aid of microbial activity (Munnecke and Samtleben 1996). In the geological past when calcified algae were rare or absent (Verbruggen et al. 2005), micrite was dominantly sourced from micritization of pre-existing carbonate grains (e.g. fossil skeletons), precipitation from inorganic seawater, or induced precipitation by calcified bacteria (Riding 1991;Kaźmierczak et al. 1996). ...
Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater. Mg isotopes are significantly (up to 5‰) fractionated during carbonate precipitation by preferential incorporation of ²⁴Mg, while hydrothermal reactions are associated with negligible Mg isotope fractionation by preferential sequestration of ²⁶Mg. Thus, the marine Mg cycle could be reflected by seawater Mg isotopic composition (δ²⁶Mgsw), which might be recorded in marine carbonate. However, carbonates are both texturally and compositionally heterogeneous, and it is unclear which carbonate component is the most reliable for reconstructing δ²⁶Mgsw. In this study, we measured Mg isotopic compositions of limestone samples collected from the early Carboniferous Huangjin Formation in South China. Based on petrographic studies, four carbonate components were recognized: micrite, marine cement, brachiopod shell, and mixture. The four components had distinct δ²⁶Mg: (1) micrite samples ranged from −2.86‰ to −2.97‰; (2) pure marine cements varied from −3.40‰ to −3.54‰, while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range (−3.27‰ to −3.75‰); (3) values for the mixture component were −3.17‰ and −3.49‰; and (4) brachiopod shells ranged from −2.20‰ to −3.07‰, with the thickened hinge area enriched in ²⁴Mg. Due to having multiple carbonate sources, neither the micrite nor the mixture component could be used to reconstruct δ²⁶Mgsw. In addition, the marine cement was homogenous in Mg isotopes, but lacking the fractionation by inorganic carbonate precipitation that is prerequisite for the accurate determination of δ²⁶Mgsw. Furthermore, brachiopod shells had heterogeneous C and Mg isotopes, suggesting a significant vital effect during growth. Overall, the heterogeneous δ²⁶Mg of the Huangjin limestone makes it difficult to reconstruct δ²⁶Mgsw using bulk carbonate/calcareous sediments. Finally, δ²⁶Mgsw was only slightly affected by the faunal composition of carbonate-secreting organisms, even though biogenic carbonate accounts for more than 90% of marine carbonate production in Phanerozoic oceans and there is a wide range (0.2‰–4.8‰) of fractionation during biogenic carbonate formation.
... Such species, which are genetically different but exhibit little or no morphological differences, are called 'cryptic' (Adams et al. 2005). The occurrence of such cryptic species has been detected previously in algae with AFLP (Mueller et al. 2005) and DNA sequence analyses (Verbruggen et al. 2005;Saunders and Lehmkuhl 2005;. ...
... H. cuneata presented significantly higher F v /F m values only at the treatment +1°C in relation to control and +4.5°C treatments (Table 3 and Fig 3) The lack of significant photosynthetic responses to rises in temperature by coralline algae, T. cylindrica and P. gymnospora are in accordance with other studies [16] supporting the adaptability of many species to variations in temperature. However, H. cuneata presented enhanced F v /F m values at modest temperature increases, which is not surprising due to its tropical nature, occurring conspicuously in tropical regions [39,40], where such variations are within the normal range. Despite this affinity to moderate higher temperatures, an increase to 4.5°C above control seawater, to an average of 31°C, led to lower F v /F m values than those observed at inferior temperature increases. ...
Climate change is a global phenomenon that is considered an important threat to marine ecosystems. Ocean acidification and increased seawater temperatures are among the consequences of this phenomenon. The comprehension of the effects of these alterations on marine organisms, in particular on calcified macroalgae, is still modest despite its great importance. There are evidences that macroalgae inhabiting highly variable environments are relatively resilient to such changes. Thus, the aim of this study was to evaluate experimentally the effects of CO2-driven ocean acidification and temperature rises on the photosynthesis of calcified macroalgae inhabiting the intertidal region, a highly variable environment. The experiments were performed in a reef mesocosm in a tropical region on the Brazilian coast, using three species of frondose calcifying macroalgae (Halimeda cuneata, Padina gymnospora, and Tricleocarpa cylindrica) and crustose coralline algae. The acidification experiment consisted of three treatments with pH levels below those occurring in the region (-0.3, -0.6, -0.9). For the temperature experiment, three temperature levels above those occurring naturally in the region (+1, +2, +4°C) were determined. The results of the acidification experiment indicate an increase on the optimum quantum yield by T. cylindrica and a decline of this parameter by coralline algae, although both only occurred at the extreme acidification treatment (-0.9). The energy dissipation mechanisms of these algae were also altered at this extreme condition. Significant effects of the temperature experiment were limited to an enhancement of the photosynthetic performance by H. cuneata although only at a modest temperature increase (+1°C). In general, the results indicate a possible photosynthetic adaptation and/or acclimation of the studied macroalgae to the expected future ocean acidification and temperature rises, as separate factors. Such relative resilience may be a result of the highly variable environment they inhabit.
... Halimeda spp. (Chlorophyta)-Broad-scale phylogeographic patterns of species of Halimeda have been elucidated using molecular analyses and niche modeling (Verbruggen et al. 2005(Verbruggen et al. , 2009a. These data clearly showed that Halimeda has been a member of the tropical flora since its early evolution, with only a few range shifts to cooler waters. ...
The tropical Pacific is a unique region to study marine algal phylogeographic patterns. The ancient age of the ocean basin, combined with the presence of numerous islands and archipelagos derived from a variety of geological and biological processes, has yielded several "cosmopolitan" algal species that likely achieved a broad distribution during the times of the Tethys Ocean. These cosmopolitan species consist, in almost all cases, of a series of lineages that can be interpreted as cryptic or pseudo-cryptic species. We review several example studies from the literature that examine phylogeographic patterns of marine algae from the tropical Pacific, and conclude (1) that in all cases the number of species discovered by molecular methods is large, (2) that the increase in diversity is correlated with sampling effort, and (3) that while morphological species are widespread in the tropics, cryptic or pseudo-cryptic species are often more localized, and even appear to have neighboring distribution patterns. These conclusions lead to a call for more large-scale collaborative studies to examine the phylogeographic trends of purportedly cosmopolitan species across the tropical Pacific.
... As these organisms must return to a suitable benthic environment within the finite larval lifetime, and must comply with the requirements of their often very complex lifecycles, they are no model candidates to resolve the question of cosmopolitanism. Among the many examples available, we mention the ascidian Ciona intestinalis (Linnaeus, 1767) (Caputi et al., 2007), the shallowwater temperate to boreal bryozoan Electra pilosa (Linnaeus, 1767) (Nikulina, Hanel & Sch€ afer, 2007), the pantropical seaweed Halimeda (Kooistra, Coppejans & Payri, 2002;Verbruggen et al., 2005), and the pantropical sea urchins Eucidaris and Tripneustes (Lessios et al., 1999;Lessios, Kane & Robertson, 2003), which all show separation by vicariance induced by land barriers and/or ocean currents. ...
It was Darwin that noted the large intraspecific diversity of the goose barnacle Lepas Linnaeus, 1758 and thought about distinct regional varieties. Today, biogeographic compartmentation is known from marine species, but data from globally occurring species remain scarce. We analysed inter- and intraspecific divergence within the epipelagic rafter Lepas from tropical and temperate oceans by means of two mitochondrial and one nuclear DNA marker. Besides phylogenetic relations, we resolved biogeography and controlling factors. Inhabiting the Southern Hemisphere, Lepas australis Darwin, 1851 shows separate populations from coastal Chile and from circum-Antarctic waters, most probably related to temperature differences in the current systems. The cosmopolitan Lepas anatifera Linnaeus, 1758 displays four regional subgroups (coastal Chile, Northeast Pacific/Oregon, the Southern Hemisphere Indopacific, and the Atlantic), and a global group, which might be an ancestral stem group. The differentiation reflects vicariance effects rooted in geological history: the closure of the Neogene Tethys in the Middle East and at the Panama Isthmus, the installation of the cool Benguela Current, differing Pleistocene currents and temperatures, and modern current systems. The extreme ecological generalists Lepas anserifera Linnaeus, 1767 and Lepas pectinata Spengler, 1793 are not differentiated, and might represent true global species. In conclusion, compartmentation of the oceans acts at the species level according to ecospace limits. For Lepas, the multitude of barriers favours allopatric speciation.
... Our results, however, show that morphological identifications of species have inflated previous assessments of species richness because some phenotypically plastic species have been recognized by several names, especially in the C. racemosa-peltata complex. For this reason, DNA-based species delimitation is a valuable tool in organisms in which morphological discrimination is difficult or impossible, such as in many algal groups (Verbruggen et al. 2005, Leliaert et al. 2009). ...
Taxonomy and species richness estimates for the genus Caulerpahave proven to be challenging due to the difficulty of assessing morphological species limits. In the present study we evaluate the taxonomy of the genus, and assess species distributions in the Eastern Tropical Pacific (ETP), based on morphology and tufA sequence data. Molecular analyses revealed six species-level clades: C. verticillata,C. sertularioides, C. cupressoides, C. serrulata, C. racemosa and C. chemnitzia (part of C. racemosa-peltatacomplex). Our results reduce species richness estimates throughout the ETP by over 54% (from 13 to 6). In accordance with recent studies, our morphological and DNA results warrant the recognition of C. chemnitzia to comprise the morphological entities C. laetevirens, C. peltata and C. vanbossea complex. We continue the use of ecads as a practical identification tool for morphological diversity below the species level present in the ETP. In addition we formally recognize the synonymy ofC. racemosa var. macrophysawith the lineage of C. racemosa proposed in recent studies. The six species of Caulerpafound in this study are of pantropical in distribution. Within the ETP region, four species have restricted distributions (C. verticillata, C. cupressoides, C. serrulata, C. racemosa), while two show a wide latitudinal distribution (C. chemnitziaand C. sertularioides).
... Because the basic distributional range of H. tuna, is restricted to the Mediterranean Sea and the Atlantic Ocean, we identified H. tuna auct. japon as H. cuneata (Verbruggen et al. 2005c). In addition, as a result of this study H. minima is newly recorded at Okinawa Island, Okinawa, Japan. ...
In order to elucidate the biodiversity of Japanese Halimeda species, we investigated molecular phylogenetic relationships using tufA and rbcL DNA sequences, and the occurrence of 9 of the 11 species previously reported in Japan was confirmed (i.e., H. borneensis, H. cuneata, H. discoidea, H. distorta, H. kanaloana, H. macroloba, H. opuntia, H. renschii and H. velasquezii). In addition, H. minima, which has not been recorded in Japan, as well as an undescribed taxon, were noticed at Okinawa Island, Okinawa, Japan. The undescribed taxon was genetically closest to H. lacunalis, but distinct from that species in having much smaller thalli, with elliptical segments and turbinate peripheral utricles. It appears to belong to the section Halimeda in the morphology of the segments, but differs from related taxa such as H. taenicola and H. tuna in its considerably smaller size and in showing fusion between the adjacent peripheral utricles. Therefore, we describe a new species Halimeda ryukyuensis sp. nov. In addition, based on morphological re-examination of the type specimen of H. lacunalis, we suggest emendation of the description of the species as having siphons completely fused in pairs or triplets at the nodes.
... This algal composed of flattened, green, calcified segments interconnected by uncalcified nodes. The entire algal body consists of a single, tubular cell that branch to form an organized network of siphons (as cited in Verbruggen et al. 2005). The genus Halimeda Lamouroux (Bryopsidales, Chlorophyta), has been recognized as a major carbonate contributor in coral reef systems (Hillis 1999). ...
Three species of the calcified benthic green algal genus Halimeda Lamouroux (Bryopsidales, Chlorophyta) collected from the three Coastal Regions of Myanmar from 1970 to 2013 were identified as H. macroloba Decaisne, H. discoidea Decaisne and H. opuntia (Linnaeus) Lamouroux. The descriptions of each taxon, mainly emphasized on the external and internal morphologies of the vegetative and reproductive structures of the specimens deposited in the Department of Marine Science, Mawlamyine University, including the living plants in the field, were presented in details. The main characteristics of all these species were comparatively described. The distribution ranges of these species along both the Coastal Regions of Myanmar and those of the world of each collected taxon were provided. All three species luxuriantly occur along the Rakhine and Tanintharyi Coastal Regions of Myanmar. Generally, the latitudinal distribution range of H. opuntia w as w ider than that of H. macroloba and H. discoidea in Myanmar waters. These three species predominated throughout the tropical to temperate coastal areas.
... As these organisms must return to a suitable benthic environment within the finite larval lifetime, and must comply with the requirements of their often very complex lifecycles, they are no model candidates to resolve the question of cosmopolitanism. Among the many examples available, we mention the ascidian Ciona intestinalis (Linnaeus, 1767) (Caputi et al., 2007), the shallowwater temperate to boreal bryozoan Electra pilosa (Linnaeus, 1767) (Nikulina, Hanel & Sch€ afer, 2007), the pantropical seaweed Halimeda (Kooistra, Coppejans & Payri, 2002;Verbruggen et al., 2005), and the pantropical sea urchins Eucidaris and Tripneustes (Lessios et al., 1999;Lessios, Kane & Robertson, 2003), which all show separation by vicariance induced by land barriers and/or ocean currents. ...
Aim We studied different species of gooseneck barnacles from the globally distributed rafting genus Lepas to examine whether the most widespread species are true cosmopolitans and to explore the factors influencing the phylogeny and biogeography of these epipelagic rafters. Location Temperate and tropical parts of the Atlantic, Pacific, and Indic oceans. Methods We used a phylogenetic approach based on mitochondrial 16S and coI sequences, and the nuclear 18S gene to elucidate patterns of inter-and intra-species divergence. Altogether, five species of Lepas from 18 confined regions of the Atlantic, Pacific and Indic oceans were analyzed.
... Many examples of cryptic species, or morphologically indistinguishable but genetically different species, are known from the marine environment (Knowlton 1993;Saunders & Lehmkuhl 2005). Molecular phylogenetic approaches have been used to successfully identify and resolve cryptic species for several 'native' floristic elements (Blomster et al. 1998;van der Strate et al. 2002;Zuccarello & West 2003;Lee et al. 2005;Verbruggen et al. 2005), though it is sometimes difficult to designate a species' status as native or introduced (Dawson et al. 2005;Heesch et al. 2009) and the term 'cryptogenic' (species that are neither clearly native nor exotic) is used for these (Carlton 1996). Genetic information is proving to be important in conservation and management efforts that involve cryptic species and their role in native ecosystem restoration. ...
Genetic information is proving to be important in conservation and management efforts that involve cryptic species and their role in native ecosystem restoration. Previous molecular studies have demonstrated that the red alga Spyridia filamentosa consists of several cryptic species. Spyridia filamentosa is considered to be a native species in Hawai'i and was recently used in preliminary seagrass meadow restoration efforts in Maunalua Bay, O'ahu. It became necessary to understand the genetic diversity of this species in the Islands and determine if there are relationships between any molecular clades of S. filamentosa and anatomical characters that might be useful (e.g. sediment capture) in habitat remediation. Both molecular and morphological (determinate branch cell dimensions) analyses revealed the presence of multiple S. filamentosa clades in Hawai'i. Nuclear [partial LSU (large subunit)] sequence and determinate branch cell data recovered two broad lineages (I and II), which are known worldwide. The mitochondrial sequence (cox2-3 spacer) data further separated samples into five distinct clades and indicated that S. filamentosa arrived in Hawai'i on at least six occasions. These results aided decisions made concerning preliminary experiments involved in seagrass habitat remediation and emphasized the importance of genetically evaluating cryptic species that are being considered for use in native ecosystem restoration or conservation.
... The differentiation of individual species is possible, when there are many segments preserved (DRAGASTAN et al. 2002 for details). In recent times, genetic DNA-studies of extant species have shown that the solely morphology-based species definition in extant Halimeda is not sufficient, but allow more genetically delineable species (HILLIS et al. 1998;VERBRUGGEN et al. 2005). ...
Halimeda misiki n. sp., a new calcareous green alga, is described from the Late Jurassic Plassen Carbonate Platform of the Northern Calcareous Alps of Austria. Other occurrences are reported from the Western and Eastern Carpathians, Morocco and Sicily/Italy. Halimeda misiki n. sp. is characterized especially by a microcrystalline (micritic) thallus appearance and cortical filaments distinctly inclined to the longitudinal axis. The new species was found in shallow water peri-reefal carbonates of platform margin facies and resediments (mass-flows, breccias, calciturbidites) in the adjacent hemipelagic basins.
German
Halimeda misiki n. sp., eine neue Kalkalge, wird aus dem Ober-Jura der Plassen-Karbonatplattform der Nördlichen Kalkalpen von Österreich beschrieben. Andere Vorkommen sind die West- und Ostkarpaten Marokko und Sizilien/Italien. Halimeda misiki n. sp. ist insbesondere durch einen mikrokristallinen (mikritischen) Thallus und deutlich zur Längsachse geneigte kortikale Filamente charakterisiert. Die neue Art wurde in peri-rezifalen Flachwasser-karbonaten einer Plattformrand-Fazies und in Resedimenten (Mass-Flows, Brekzien, Calciturbiditen) in angrenzenden hemipelagischen Becken gefunden.
Simple Summary
This inventory represents the first complete inventory of seaweeds (benthic brown, red, and green algae) and seagrasses from the Hawaiian Islands. We present taxonomic records compiled from the literature which include many recent descriptions of new species. Taxonomic records are accompanied by additional information allowing an assessment of the degree of molecular confirmation: whether the record has been verified by a match to DNA sequences from a type specimen, topotype sequences, or regional DNA sequences. In addition, taxa that have been identified solely based on morphology are indicated. In the face of numerous threats to biodiversity in the coming decades, it is hoped that this inventory will provide baseline data sets against which future changes may be compared.
Abstract
This updated list is composed of a total of 661 records, which includes 71 brown algae, 450 red algae, 137 green algae, and three seagrasses, with an overall rate of endemism of 13.2%. Almost half (46.7%) of the Hawaiian records presented here are represented by at least one DNA sequence, while 16.3% are confirmed through a DNA sequence match to a topotype, and 6.7% are confirmed through a DNA sequence match to a type specimen. The data are presented in the context of the natural history of the Hawaiian Islands, which is heavily influenced by the volcanic hotspot origin of the archipelago in the middle of the Pacific Ocean, as well as the important cultural role of seaweeds and other marine plants in Hawai‘i, and the current threats to marine ecosystems, which include the introduction and proliferation of a number of invasive marine macroalgae.
The flora and fauna of Southeast Asia are exceptionally diverse. The region includes several terrestrial biodiversity hotspots and is the principal global hotspot for marine diversity, but it also faces the most intense challenges of the current global biodiversity crisis. Providing reviews, syntheses and results of the latest research into Southeast Asian earth and organismal history, this book investigates the history, present and future of the fauna and flora of this bio- and geodiverse region. Leading authorities in the field explore key topics including palaeogeography, palaeoclimatology, biogeography, population genetics and conservation biology, illustrating research approaches and themes with spatially, taxonomically and methodologically focused case studies. The volume also presents methodological advances in population genetics and historical biogeography. Exploring the fascinating environmental and biotic histories of Southeast Asia, this is an ideal resource for graduate students and researchers as well as environmental NGOs.
The flora and fauna of Southeast Asia are exceptionally diverse. The region includes several terrestrial biodiversity hotspots and is the principal global hotspot for marine diversity, but it also faces the most intense challenges of the current global biodiversity crisis. Providing reviews, syntheses and results of the latest research into Southeast Asian earth and organismal history, this book investigates the history, present and future of the fauna and flora of this bio- and geodiverse region. Leading authorities in the field explore key topics including palaeogeography, palaeoclimatology, biogeography, population genetics and conservation biology, illustrating research approaches and themes with spatially, taxonomically and methodologically focused case studies. The volume also presents methodological advances in population genetics and historical biogeography. Exploring the fascinating environmental and biotic histories of Southeast Asia, this is an ideal resource for graduate students and researchers as well as environmental NGOs.
The flora and fauna of Southeast Asia are exceptionally diverse. The region includes several terrestrial biodiversity hotspots and is the principal global hotspot for marine diversity, but it also faces the most intense challenges of the current global biodiversity crisis. Providing reviews, syntheses and results of the latest research into Southeast Asian earth and organismal history, this book investigates the history, present and future of the fauna and flora of this bio- and geodiverse region. Leading authorities in the field explore key topics including palaeogeography, palaeoclimatology, biogeography, population genetics and conservation biology, illustrating research approaches and themes with spatially, taxonomically and methodologically focused case studies. The volume also presents methodological advances in population genetics and historical biogeography. Exploring the fascinating environmental and biotic histories of Southeast Asia, this is an ideal resource for graduate students and researchers as well as environmental NGOs.
The flora and fauna of Southeast Asia are exceptionally diverse. The region includes several terrestrial biodiversity hotspots and is the principal global hotspot for marine diversity, but it also faces the most intense challenges of the current global biodiversity crisis. Providing reviews, syntheses and results of the latest research into Southeast Asian earth and organismal history, this book investigates the history, present and future of the fauna and flora of this bio- and geodiverse region. Leading authorities in the field explore key topics including palaeogeography, palaeoclimatology, biogeography, population genetics and conservation biology, illustrating research approaches and themes with spatially, taxonomically and methodologically focused case studies. The volume also presents methodological advances in population genetics and historical biogeography. Exploring the fascinating environmental and biotic histories of Southeast Asia, this is an ideal resource for graduate students and researchers as well as environmental NGOs.
Plasticity in morphology is a common phenomenon of aquatic plants. Halimeda (Chlorophyta: Halimedaceae) is usually supersaturated with calcium carbonate and is found in tropical and subtropical regions. Among members of Halimeda, both species including Halimeda macroloba and H. opuntia, often occur in different habitats. Haplotype diversity and network of Halimeda were reported in the different sea and oceanic systems. However, there are no reports of the genetic diversity of Halimeda in Vietnamese waters. This present study carried out sample collections along the coast of Southern Viet Nam, including the coast sites, offshore islands, and Spratly (Truong Sa) islands. External morphological and anatomical characteristics of two dominant species, Halimeda macroloba and H. opuntia, were caparisoned. The genetic marker tufA was applied to find the haplotype diversity and network among Vietnamese and worldwide populations. The results showed that high morphology exists in both species. In contrast, the genetic variation in H. macroloba is very low, and H. opuntia tends to form a distinct group. We suggest that more samples of two species from other locations in Northern Vietnam be included.
The chlorophyte genus Halimeda is common in tropical waters but gaps still exist in the understanding of the biogeographical distributions of its species in Southeast Asia, particularly in Malaysia. During a study into the ecological functioning of reefs in a marine park (the Sembilang–Seri Buat group of islands, Pahang, Malaysia) along the eastern coast of Peninsular Malaysia, a previously unreported
community of sand-dwelling Halimeda was discovered on a shallow reef flat (water depths of 1-2 m). We randomly collected 63 individuals and identified them using defining morphological and anatomical characteristics. The collection consisted of Halimeda borneensis, H. discoidea, H. macroloba, H. opuntia, and H. taenicola. Halimeda borneensis was the most collected (52 individual explants) in our
study site. We report that H. taenicola is a new record for the eastern coast of Peninsular Malaysia, which is also a first biogeographical report of this species for the area spanning the Gulf of Thailand and
towards the coastal areas to the east of Singapore. This study together with past records on Halimeda in the immediate surroundings show a total of six Halimeda species in the area, a localised coastal diversity uncommon to this part of the South China Sea.
Iron and manganese are the important redox-sensitive elements in the ocean. Previous studies have established a series of paleo-depositional redox proxies based on the form and content of iron in sedimentary rocks (e.g., degree of pyritization, FeHR/FeT, Fe/Al). These proxies were developed and applied on siliciclastic-rich marine sediments. Although marine carbonate rocks are generally considered to preserve the geochemical signals of ancient seawater, neither Fe nor Mn content in marine carbonate rocks (Fecarb, Mncarb) has been independently used as a proxy to quantify environmental cues in paleo-oceans. Both Fe and Mn are insoluble in oxic conditions (Fe2O3, Fe(OH)3, MnO2), while their reduced forms (Fe²⁺ and Mn²⁺) are soluble. Therefore, oxic seawater should have low concentrations of dissolved Fe²⁺ and Mn²⁺, and accordingly carbonate rocks precipitated from oxic seawater should have low Fecarb and Mncarb, and vice versa. To evaluate whether Fecarb and Mncarb can be used to quantify oxygen fugacity in seawater, we measured Fecarb and Mncarb of Upper Devonian marine carbonate rocks collected from nine sections in South China. Fecarb of intraplatform basin samples was significantly higher than that of shelf samples, while shelf and basin samples had comparable Mncarb. The modeling result indicates that the dramatic difference in Fecarb cannot be explained by variation in oxygen fugacity between the shelf and basin seawater. Instead, both Fecarb and Mncarb appear to be more sensitive to benthic flux from sediment porewater that is enriched in Fe²⁺ and Mn²⁺. Porewater Fe²⁺ and Mn²⁺ derive from bacterial iron and manganese reduction; flux was controlled by sedimentation rate and the depth of the Fe(Mn) reduction zone in sediments, the latter of which is determined by oxygen fugacity at the water–sediment interface. Thus, high Fecarb of the basin samples might be attributed to low sedimentation rate and/or low oxygen fugacity at the seafloor. However, invariant Mncarb of the shelf and basin samples might be the consequence of complete reduction of Mn in sediments. Our study indicates that marine carbonate rocks may not necessarily record seawater composition, particularly for benthic carbonate rocks. The influence of benthic flux might cause carbonate rocks’ geochemical signals to deviate significantly from seawater values. Our study suggests that interpretation of geochemical data from carbonate rocks, including carbonate carbon isotopes, should consider the process of carbonate formation.
Brackish marine and brackish continental environments are fundamentally different from a compositional perspective. Brackish water is often defined as having salinity lower than that of standard seawater but higher than that of freshwater, but less regard is given to the origin of the salts involved. The simple dilution of standard seawater by freshwater in a coastal or estuarine setting constitutes a brackish environment, but so do lakes where continental fresh water is impounded and becomes more saline through a variety of solute evolution pathways. The range of potential compositions of brackish lake water is diverse and includes water with “seawater-like” compositions. Isolated brackish lake environments located hundreds of kilometers inland can evolve towards sodium chloride-dominated, low alkalinity environments that mimic the composition of brackish seawater environments. These types of lakes can harbor a variety of continentally invasive but typically marine organisms, including but not limited to algae, foraminifers, mollusks, diatoms, and crustaceans. Distinguishing brackish marine from brackish lake environments in the geologic record can be difficult. In this paper, the enigmatic late Miocene and early Pliocene southern Bouse Formation of southern Arizona and California, USA, considered by many to represent a marine transgression along the lower Colorado River corridor, is discussed within a broad framework that incorporates hydrochemical, biogeographical, and species niche concepts. A brackish lake interpretation provides a powerful platform that can comprehensively account for the enigmatic mixed marine and continental fossil assemblage and possible tidal rhythmites that feature prominently in the southern Bouse Formation controversy. A review of the broader regional (paleo)environmental context for the southern Bouse supports a sodium chloride-dominated, low alkalinity, mildly brackish (10-5 ppt) Colorado River-fed lake depositional environment that was populated by an intriguing but predictable array of euryhaline, opportunistic, and continentally invasive marginal marine organisms.
Las macroalgas bénticas son consideradas un componente fundamental en el mantenimiento y equilibrio de los arrecifes coralinos. Dada la importancia de suministrar información sobre florística y distribución de nuevos taxones de este grupo vegetal, se determinó la composición de especies de macroalgas en los arrecifes submareales del Parque Nacional Archipiélago Los Roques, Venezuela. Las muestras se colectaron mediante buceo autónomo entre 12-22 m de profundidad en nueve localidades del parque, durante agosto y septiembre de 2011. Se identificó un total de 53 especies: cinco pertenecientes al Phylum Chlorophyta, cinco al Phylum Ochrophyta y 43 al Phylum Rhodophyta, 29 de las cuales representan adiciones para el parque. El hecho de que más del 50% de los registros citados son nuevos para esta localidad y que hasta el momento toda la investigación se había realizado en ambientes intermareales, enfatiza la importancia de la exploración submareal para este parque y otras regiones de Venezuela
A complete checklist of intertidal to shallow subtidal marine green seaweeds (Chlorophyta) growing on the subtropical island of Hainan (China) is presented here for the first time. It covers data from extensive recent (1990-2009) and historical (1933-1935) collections, and additional published records from various time periods. Data were analyzed by time period. We postulate that environmental changes on Hainan Island documented since the 1980s (e.g., degradation of coral reefs, development of tourism and mariculture farms) are reflected in the green algal species complement and in the dominance or absence of specific algal groups during different time periods. In total, 105 green algal taxa were recorded, including 37 new to Hainan Island, and 18 new records for China. There was a clearly evident change in floristic composition between early and recent collections. In the 1930s, there was a dominance of Caulerpaceae, Codiaceae and Cladophoraceae. By 1990/1992, the numbers of Ulvaceae had increased 1.6-fold and numbers of Cladophoraceae 1.7-fold. Both families contain many opportunistic species that prefer nutrient-enriched or degraded environments. At the same time, species richness of Codiaceae, Caulerpaceae and Udotaceae, families with complex thallus structures, decreased considerably. The floristic differences between the 1990/1992 and 2008/2009 collections were minor.
This second paper in a monographic series on the marine algae of French Polynesia gives a detailed coverage of the species of Chlorophyceae occurring in these islands. A total of 81 taxa are presented; of these, 23 represent new records for the local flora, 1 (Halimeda heteromorpha) is a new species and 2 (Microdictyon sp. and Struveopsis sp.) are newly discovered taxa. The benthic marine green algal flora has most affinities with the neighbouring Cook Islands (Sørensen Index of 0.43) but only with 44% of shared species with that archipelago, while 69 and 64% of species are shared with the Fijian and Micronesian islands, respectively. About 75% of the flora is shared with the Indian and Pacific Ocean in general; 3 species (or about 4% of the total flora) seem restricted to French Polynesia.
It is widely acknowledged that the Southeast Asian region is an area of outstanding biological and geological interest. It is an area of exceptional biodiversity which contains both marine and terrestrial biodiversity hotspots (Myers et al. 2000, Roberts et al. 2002). The convoluted and still highly active, tectonic history of the region has resulted in a complex archipelago characterised by highly localised terrestrial faunas with large numbers of endemic species (Hall 2002, Sodhi et al. 2004). Terrestrial hotspots are defined as areas of exceptional endemism (usually combined with some measure of environmental damage) (Meyers et al. 2000). This focus on endemism has resulted in the identification of three small regional terrestrial hotspots within the Indo-Australian Archipelago (IAA). The marine system stands in marked contrast to the terrestrial pattern, with the IAA sitting in the middle of a single massive global marine hotspot. This feature dominates patterns of tropical marine biodiversity and spans over two thirds of the world’s tropical equatorial oceans. This pattern is observed in most tropical shallow marine taxa (see review of Hoeksema 2007). Although the exact location of the most diverse area differs between taxa, in all cases, the IAA contains the hottest part of the world’s largest biodiversity hotspot (Fig 9.1).
13.1.1 The Indo-Australian Archipelago and its freshwater fauna Th e Indo-Australian Archipelago (IAA) houses one of the highest levels of spe-cies richness and endemism in the world, encompassing four of the world's 25 biodiversity 'hotspots', which coalesce within this region in Southeast Asia (Myers et al. 2000). Southeast Asia covers only around 4% of the earth's surface, but houses some 20–25% of global fauna and fl ora (Mittermeier et al. 1999 , 2005 , Myers et al. 2000). Freshwater biodiversity levels are also extremely high in Southeast Asia, although very understudied and undervalued (Dudgeon et al. 2006 , and refer-ences therein). Freshwater biodiversity within this species-rich region is often overlooked by conservationists; for example, only 0.6% of papers published in the conservation literature from 1992–2001 dealt with Asian freshwater biodiversity (Dudgeon 2003). Around 15% of global freshwater fauna are found in Indonesia
The distribution of species in their environment is largely defined by habitat characteristics. Both species and habitat distributions can be used to define conservation areas, especially in highly diversified ecosystems like coral reefs where biodiversity inventories are lacking. The main objective of this study was to test the relationship between multi-taxa community structure (defined by richness, species lists, and taxonomic distinctness) and habitat typology in the Man and Biosphere UNESCO Reserve of Baa Atoll (Maldives). Species richness per taxon was described at 18 stations located on different habitats mapped using high resolution satellite imagery. A total of 1012 species were described including 178 macroalgae, 173 corals, 121 hydroids, 351 fish and 189 (other) macro-invertebrates. Rarity was extremely high for macro-invertebrates, algae and hydrozoans. The results highlighted a marked difference in species composition between stations for macro-algae and corals but not for other groups (hydroids, fish and macro-invertebrates). These distribution patterns were not strongly correlated to differences in habitat characteristics, which created a weak spatial structure of communities between habitats probably caused by differential exposure of atolls to monsoons and the 1998 bleaching event. Community differences between stations were often due to rarity. Therefore, identifying a network of protected areas that includes occurrences of all species may pose challenges. This is overcome by conservation planning scenarios using medium-size (of the order of 1 km2) management units.
Halimeda Lamouroux constitutes a genus of calcified and segmented green seaweeds within the Bryopsidales. Molecular phylogenetic assessments have uncovered five principal monophyletic lineages within the genus. In the present study we define these lineages morphologically. We gathered morphological data from specimens used in the molecular analyses as well as from collections having a similar morphology and originating from the same geographical region. Starting from the lineages and their morphological synapomorphies, we define and illustrate five natural sections within Halimeda. All or most medullary siphons traversing the nodes between segments fuse into a single unit in specimens of lineage 1 (section Rhipsalis), and segments at the thallus base fuse with one another. Medullary siphons of specimens in lineage 2 (section Micronesicae) traverse the node without fusing. Medullary siphons of specimens in lineage 3 (section Halimeda) divide frequently below the nodes and become entangled among one another. The segments of specimens in this lineage possess a continuous uncorticated band along the distal perimeter instead of three or more pits as encountered in segments of specimens in all other lineages. Members of lineage 4 (section Pseudo-opuntia) possess club-shaped subperipheral utricles in their cortical region. Medullary siphons of specimens in lineage 5 (section Opuntia) fuse over only a short distance at the nodes and retain their identity. Apart from these synapomorphies, the lineages can be delimited further by a characteristic combination of symplesiomorphies and homoplasies. In addition we examined the morphology of H. bikinensis Taylor, a species not included in the molecular analyses, and discuss its ambiguous position in our sectional system.
To date, the majority of molecular genetic studies in algae have utilized a fairly limited range of markers such as the plastid rbcL gene and spacer, the mitochondrial cox2-3 spacer or the nuclear ribosomal DNA and spacers. The lack of available markers has been particularly problematic in studies of within-species variation. Whilst microsatellites are now being developed in many algal species, there remains a need for universal markers that can be applied to a wide range of species. The increasing availability of complete plastid genome sequences for several algae has allowed us to develop two sets of universal primers, similar to those available in higher plants, for the amplification of coding and non-coding regions of the plastid genome in red and green algae. These markers are expected to be useful in a broad range of algal population genetic and phylogenetic studies.
Halimeda Lamouroux constitutes a genus of calcified and segmented green seaweeds within the Bryopsidales. Molecular phylogenetic assessments have uncovered five principal monophyletic lineages within the genus. In the present study we define these lineages morphologically. We gathered morphological data from specimens used in the molecular analyses as well as from collections having a similar morphology and originating from the same geographical region. Starting from the lineages and their morphological synapomorphies, we define and illustrate five natural sections within Halimeda. All or most medullary siphons traversing the nodes between segments fuse into a single unit in specimens of lineage 1 (section Rhipsalis), and segments at the thallus base fuse with one another. Medullary siphons of specimens in lineage 2 (section Micronesicae) traverse the node without fusing. Medullary siphons of specimens in lineage 3 (section Halimeda) divide frequently below the nodes and become entangled among one another. The segments of specimens in this lineage possess a continuous uncorticated band along the distal perimeter instead of three or more pits as encountered in segments of specimens in all other lineages. Members of lineage 4 (section Pseudo-opuntia) possess club-shaped subperipheral utricles in their cortical region. Medullary siphons of specimens in lineage 5 (section Opuntia) fuse over only a short distance at the nodes and retain their identity. Apart from these synapomorphies, the lineages can be delimited further by a characteristic combination of symplesiomorphies and homoplasies. In addition we examined the morphology of H. bikinensis Taylor, a species not included in the molecular analyses, and discuss its ambiguous position in our sectional system.
Molecular data have had a profound impact on the field of plant systematics, and the application of DNA-sequence data to phylogenetic ,problems ,is now ,routine. The majority of data ,used in plant molecular phylogenetic studies derives from chloroplast DNA and nuclear rDNA, while the use of low-copy nuclear genes has not been widely adopted. This is due, at least in part, to the greater difficulty of isolating and characterising low-copy nuclear genes relative to chloroplast and rDNA sequences ,that are readily amplified with universal primers. The higher level of sequence variation characteristic of low-copy nuclear genes, however, often compensates for the experimental effort required to obtain them. In this review, we briefly discuss the strengths and limitations of chloroplast and rDNA sequences, and then focus our attention on the use of low-copy nuclear sequences. Advantages of low-copy ,nuclear sequences ,include a higher ,rate of evolution ,than for organellar sequences, the potential to accumulate datasets from multiple unlinked loci, and bi-parental inheritance. Challenges intrinsic to the ,use of low-copy ,nuclear sequences ,include distinguishing orthologous ,loci from divergent paralogous loci in the same gene family, being mindful of the complications arising from concerted evolution or recombination among paralogous sequences, and the presence of intraspecific, intrapopulational and intraindividual polymorphism. Finally, we provide a detailed protocol for the isolation, characterisation and use of low-copy nuclear sequences for phylogenetic studies. SB03 015 Us e of n uclear ge nesi n pl antphyl ogeny R. L. S ma ll etal .
Molecular data have had a profound impact on the field of plant systematics, and the application of DNA-sequence data to phylogenetic problems is now routine. The majority of data used in plant molecular phylogenetic studies derives from chloroplast DNA and nuclear rDNA, while the use of low-copy nuclear genes has not been widely adopted. This is due, at least in part, to the greater difficulty of isolating and characterising low-copy nuclear genes relative to chloroplast and rDNA sequences that are readily amplified with universal primers. The higher level of sequence variation characteristic of low-copy nuclear genes, however, often compensates for the experimental effort required to obtain them. In this review, we briefly discuss the strengths and limitations of chloroplast and rDNA sequences, and then focus our attention on the use of low-copy nuclear sequences. Advantages of low-copy nuclear sequences include a higher rate of evolution than for organellar sequences, the potential to accumulate datasets from multiple unlinked loci, and bi-parental inheritance. Challenges intrinsic to the use of low-copy nuclear sequences include distinguishing orthologous loci from divergent paralogous loci in the same gene family, being mindful of the complications arising from concerted evolution or recombination among paralogous sequences, and the presence of intraspecific, intrapopulational and intraindividual polymorphism. Finally, we provide a detailed protocol for the isolation, characterisation and use of low-copy nuclear sequences for phylogenetic studies. SB03 015 Us e of nuclear genes in pl ant phylogeny R. L. S ma ll et al .
The subtidal plant communities of the Socotra Archipelago were studied by means of quadrat sampling. Ordination and statistical analyses revealed 6 distinct clusters corresponding to the geographic location and the physico-chemical factors. The north coast of Socotra Island supports algae commonly found in the Indian Ocean, with an intermediate species richness and alpha diversity for the archipelago. This entity includes 2 species-poor subentities: the seagrass beds and the coral-dominated communities. The transition zone is an overlapping area between Socotra's north and south coast where the greatest similarity in community structure with the upwelling flora of the south coast is found, owing to similar environmental conditions. This zone is subject to intense current patterns favouring a pronounced diversity of red algae. The south coast features the highest number of recorded species and a lower affinity with the (sub-)tropical Indian Ocean flora, and is marked by disjunctly distributed species. The plant communities of the outer islands comprise a mixture of the other entities due to the drastically changing seasonal environmental conditions in a limited coastal area. The intermediate character of this entity, i.e. ongoing competition amongst biota without reaching a climax in the vegetation succession, is reflected in the vegetation analyses and the biogeographic comparison.
The tropical green algal genus Halimeda is one of the best studied examples of pseudo-cryptic diversity within the algae. Previous molecular and morphometric studies revealed that within Halimeda section Rhipsalis, Halimeda incrassata included three pseudo-cryptic entities and that the morphological boundaries between H. incrassata and Halimeda melanesica were ill-defined. In this paper, the taxonomy of H. incrassata is revised: two pseudo-cryptic entities are described as new species, Halimeda kanaloana and Halimed heteromorpha, while H. incrassata is redefined to encompass a single, monophyletic entity. Similarities and differences between the three species and H. melanesica are discussed. Monophyly of H. heteromorpha, which was questioned in a former study, is reinvestigated using sets of 32 ITS1–ITS2 and 21 plastid rps3 sequences and various alignment and inference methods. The phylogenetic relationships within Halimeda section Rhipsalis are inferred from nuclear 18S–ITS1–5.8S–ITS2 and concatenated plastid sequences (tufA & rpl5–rps8–infA) and interpreted in a biogeographic context.
ABSTRACTA new species, Halimeda hummii, and a new variety of Halimeda cryptica Colinvaux and Graham both originally collected from the edge of the continental shelf on the southwest coast of Puerto Rico are newly described. The new species is irregular in its segment morphology and is the smallest species of Halimeda presently known. Halimeda cryptica var. acerifolia from deep water possesses distinctive segments resembling maple leaves. Halimeda copiosa Goreau and Graham and typical H. cryptica are also collected in deep water and are newly recorded from Puerto Rico.
Phylogenetic relationships were inferred from parsimony and distance analyses of nuclear small-subunit ribosomal DNA sequences taken from 14 species representing 8 of the 11 extant genera in the Dasycladales. Of 1733 aligned positions, 412 (23.8%) were variable and 251 (61%) of those were phylogenetically informative within the Dasycladales. Secondary structure was analyzed and taken into account during all phases of data analysis. Robustness of the trees was assessed using bootstrap analysis and g1 statistics of tree-length decay. Strongly supported branches were robust to all methods of analysis regardless of weighting schemes used. The secondary structure of the 18S within the Dasycladales agrees with that of other green algae with the exception of a shared deletion in stemloop E10-1 (ca. 13 nucleotides long), which provides additional support for the uniqueness of this monophyletic group. A molecular clock was calibrated from the dasyclad fossil record and suggests a radiation of the Acetabulariaceae at 120 ± 30 million years (Ma) ago and the Dasycladaceae 215 ± 40 Ma ago. The split of the two lineages from a shared ancestor is estimated at 265 ± 50 Ma ago. Within the Dasycladaceae, Neomeris and Cymopolia are sister taxa, as are Batophora and Chlorocladus. Bornetella groups with the Neomeris and Cymopolia clade in 78% of the bootstrap replicates. Relationships among the Acetabulariaceae show that Acetabularia and Polyphysa do not form monophyletic groups as presently circumscribed. No evidence indicates that Acicularia is the oldest genus. Halicoryne, Chalmasia, and Dasycladus were not included in the analysis. Molecular data provide afresh background perspective from which to discuss the evolution of one of the most ancient lineages of green plants.
Molecular data have had a profound impact on the field of plant systematics, and the application of DNA-sequence data to phylogenetic problems is now routine. The majority of data used in plant molecular phylogenetic studies derives from chloroplast DNA and nuclear rDNA, while the use of low-copy nuclear genes has not been widely adopted. This is due, at least in part, to the greater difficulty of isolating and characterising low-copy nuclear genes relative to chloroplast and rDNA sequences that are readily amplified with universal primers. The higher level of sequence variation characteristic of low-copy nuclear genes, however, often compensates for the experimental effort required to obtain them. In this review, we briefly discuss the strengths and limitations of chloroplast and rDNA sequences, and then focus our attention on the use of low-copy nuclear sequences. Advantages of low-copy nuclear sequences include a higher rate of evolution than for organellar sequences, the potential to accumulate datasets from multiple unlinked loci, and bi-parental inheritance. Challenges intrinsic to the use of low-copy nuclear sequences include distinguishing orthologous loci from divergent paralogous loci in the same gene family, being mindful of the complications arising from concerted evolution or recombination among paralogous sequences, and the presence of intraspecific, intrapopulational and intraindividual polymorphism. Finally, we provide a detailed protocol for the isolation, characterisation and use of low-copy nuclear sequences for phylogenetic studies. S B 0 3 0 1 5 U s e o f n u c l e a r g e n e s i n p l a n t p h y l o g e n y R . L . S ma l l e t a l . Introduction The impact of molecular data on the field of plant systematics can hardly be overstated. In combination with explicit methods for phylogenetic analysis, molecular data have reshaped concepts of relationships and circumscriptions at all levels of the taxonomic hierarchy (Qiu et al. 1999; Soltis et al. 1999; Crawford 2000). As molecular phylogenetic studies have accumulated, it has become apparent that different molecular tools are required for different questions because of varying rates of sequence evolution among genomes, genes and gene regions. The choice of molecular tool is of paramount importance to ensure that an appropriate level of variation is recovered to answer the phylogenetic question at hand. Nonetheless, the plant systematics community is using only a small fraction of the available molecular tools. The preponderance of molecular data applied to plant systematics problems come from two sources: chloroplast DNA (cpDNA) or nuclear ribosomal DNA (rDNA). While the contributions of cpDNA and rDNA to plant systematics are undeniable, reliance on these tools to the exclusion of other, perhaps more appropriate, tools is pervasive (Alvarez and Wendel 2003). Alternatives to cpDNA and rDNA include both mitochondrial (mtDNA) and nuclear (nDNA) sequences other than rDNA. Because of its generally slow rate of sequence evolution and fast rate of structural evolution (Palmer 1992; Palmer et al. 2000), mtDNA generally has been ignored by plant systematists as a potential source of data (but see e.g. Qiu et al. 1998, 1999; Freudenstein and Chase 2001; Anderberg et al. 2002; Sanjur et al. 2002). For this reason, mtDNA will not be considered further in this review. Nuclear sequences other than rDNA represent most of the DNA contained in any given cell, comprising both high-copy repetitive DNA (e.g. transposons, centromeric and telomeric repeats), and low-to moderate-copy DNA elements, including the majority of genes. The evolutionary dynamics of these two classes of DNA can be dramatically different. For example, repetitive DNA may experience non-Mendelian transmission, be subject to concerted evolution, and/or be mobile within a genome (e.g.
The genus Caulerpa consists of about 75 species of tropical to subtropical siphonous green algae. To better understand the evolutionary history of the genus, a molecular phylogeny was inferred from chloroplast tufA sequences of 23 taxa. A sequence of Caulerpella ambigua was included as a potential outgroup. Results reveal that the latter taxon is, indeed, sister to all ingroup sequences. Caulerpa itself consists of a series of relatively ancient and species-poor lineages and a relatively modern and rapidly diversifying clade, containing most of the diversity. The molecular phylogeny conflicts with the intrageneric sectional classification based on morphological characters and an evolutionary scheme based on chloroplast ultrastructure. High bootstrap values support monophyly of C. mexicana, C. sertularioides, C. taxifolia, C. webbiana, and C. prolifera, whereas most other Caulerpa species show para- or polyphyly.
The desert theory of the Mediterranean surfaced in 1970 following the deep-sea drilling cruise aboard the Glomar Challenger. This envisaged the Mediterranean basin to have been separated from the Atlantic Ocean about 6 million years ago and to have dried up with the floor at about 3000 m depth resembling a gigantic Death Valley on which thick evaporite salts accumulated; at the beginning of the Pliocene, Atlantic water is though to have surged back into the basin as a giant waterfall at Gibraltar. The author argues, however, that the configuration of the Mediterranean was considerably different at the end of the Miocene than at present and that the seafloor remained almost continually covered by very saline waters, perhaps one hundred to several hundred metres deep. -J.G.Harvey
Completes the revision of fossil Chlorophyceae Algae (green algae) undertaken by the Groupe francais d'etude des Algues fossiles. For each species the original diagnosis or description is given, followed by a translation either in French or English. The dimensions, the stratigraphic and geographical distribution, the association with flora and fauna, an in-depth discussion and a bibliography are given for each species. A table representing the whole of the stratigraphic distribution, as well as several outline drawings, is included.-from English summary
The main purposes are to collate information of the region, to review marine systems and processes in the intertidal and shallow sublittoral parts of the Arabian seas, and to highlight human utilisation and environmental consequences. The first section presents the geological, geographical, climatic and oceanographic background to the area. The second section examines what is known of the region's marine communities, interpreting the relationships between the marine systems and physical conditions for: reefs and coral communities; coral reef fish assemblages; other reef components and processes; seaweeds and seasonality; seagrasses and other dynamic substrates; intertidal areas - mangal associated ecosystems, marshes, sabkha and beaches; and the pelagic system. The next section synthesizes and concludes the biogeographical material and interprets the effects of natural stress on the biota. The final section describes and discusses the human use and management of the region, including fisheries. -after Authors
Twenty species of Rhodophyta that have not previously been recorded for South Africa have been found on the coast of Natal. All but six species are new to the East African region, but have been recorded from other distant regions of the world. It is particularly noteworthy that fifteen of the twenty species were previously known to occur in Australia, six of the fifteen not having been found anywhere but in Australia before this time. An additional species, Dasyclonium incisum, has been known to occur only in Australia and New Zealand before this report. Two species, Anotrichium tenue and Wrangelia argus, are probably pan-tropical to subtropical species and a few others such as Halymenia dilatata, Sebdenia polydactyla, Symphyocladia marchantioides and Pterosiphonia spinifera may eventually be shown to belong in a similar category.
A new, deep water species of Halimeda, H. magnidisca, has been found on the Great Barrier Reef of northeastern Australia. It is characterized by prominent stipe-like lower axes, sand-anchored bulbous bases, and the largest segments (up to 55 mm wide and 40 mm long) so far recorded in the genus. The new species is described anatomically and compared to other species of Halimeda with large segments. The peripheral utricles of H. magnidisca are smaller than those recorded for H. gigas and H. tuna, while the bell-shaped peripheral utricles of H. macroloba are quite distinct from the characteristic goblet-shaped utricles of the new species. A comparison is also made with H. cuneata which has similarly shaped peripheral utricles. The presence of cushion or ‘stalk’-like structures between the segments of H. cuneata, lack of lower stipe-like segments, and smaller segment size distinguish this species from H. magnidisca.
A new, deep water species of Halimeda, H. magnidisca, has been found on the Great Barrier Reef of northeastern Australia. It is characterized by prominent stipe-like lower axes, sand-anchored bulbous bases, and the largest segments (up to 55 mm wide and 40 mm long) so far recorded in the genus. The new species is described anatomically and compared to other species of Halimeda with large segments. The peripheral utricles of H. magnidisca are smaller than those recorded for H. gigas and H. tuna, while the bell-shaped peripheral utricles of H. macroloba are quite distinct from the characteristic goblet-shaped utricles of the new species. A comparison is also made with H. cuneata which has similarly shaped peripheral utricles. The presence of cushion or ‘stalk’-like structures between the segments of H. cuneata, lack of lower stipe-like segments, and smaller segment size distinguish this species from H. magnidisca.
Allozyme variation in species of the mangrove genus Avicennia was screened in 25 populations collected from 22 locations in the Indo-West Pacific and eastern North America using 11 loci. Several fixed gene differences supported the specific status of Avicennia alba, A. integra, A. marina, and A. rumphiana from the Indo-West Pacific, and A. germinans from the Atlantic-East Pacific. The three varieties of A. marina, var. marina, var. eucalyptifolia, and var. australasica, had higher genetic similarities (Nei's I) and no fixed gene differences, confirming their conspecific status. Strong genetic structuring was observed in A. marina, with sharp changes in gene frequencies at the geographical margins of varietal distributions. The occurrence of alleles found otherwise in only one variety, in only immediately adjacent populations of another variety, provided evidence of introgession between varieties. The varieties appear to have diverged recently in the Pleistocene and are apparently not of ancient Cretaceous origin, as suggested earlier. Despite evidence of high degrees of outcrossing, gene flow among populations was relatively low (Nem ≤ 1-2), except where populations were geographically continuous, questioning assumptions that these widespread mangrove species achieve high levels of long-distance dispersal.
... Ideally, each hypothesis of the history of a group of organisms should be evaluated by considering all of the compatible gene trees . ... Syst. Biol. 46:523–536. SANG, T., AND Y. ZHONG. 2000. Testing hybridization hy- potheses based on incongruent gene trees . Syst. Biol. ...
Traditional taxonomy of the segmented green algal genus Halimeda is largely based on descriptive expressions of thallus habit, segment shape and anatomical structures. In the course of the last decade, molecular phylogenetic studies have revealed non-mono- phyly and cryptic diversity in several species. In an attempt to tackle the taxonomic problems that were raised by these molecular studies, a combined molecular and morpho- metric method was developed. In this study, a morphometric pilot data set is explored. This resulted in the discovery of segments aberrant in morphology and/or anatomy. These are primarily apical and non-calcified segments, and segments from the basal part of the algal body. To answer the question whether incorporation of comparison of discriminant analy- ses that included and excluded deviant segments demonstrated the negative influence of such segments on the taxonomic power of the data. Omitting non-calcified and apical segments and segments from the basal thallus region yielded the same results as the exclu- sion of all deviant segments, irrespective of their location in the algal body. This result per- mits a simple recommendation towards precluding these types of segments from further studies. Anatomy / Bryopsidales / Chlorophyta / deviant segments / discriminant analysis / Halimeda / morphology / morphometrics / taxonomy
Until now, Halimeda cuneata has only been known from the Indo-Pacific region. Although this taxon is represented abundantly in local herbarium collections, its presence has never been registered for Brazil. Previous studies have probably mistaken Brazilian material of H. cuneata for H. discoidea or H. tuna, when not reported as Halimeda sp. Besides giving a detailed morphological description, we describe the gametangia and include information on ultrastructure and histochemistry, aspects that have been neglected in the characterization of the genus. The discovery of H. cuneata in Brazil provides additional evidence regarding the similarities between the Indian Ocean and tropical southwestern Atlantic marine flora.
Microspectrophotometry with the DNA-localizing fluorochrome 3',6-diamidino-2-phenylindole (DAPI) was used to estimate nuclear genome sizes in 12 species representing two families of the Dasycladales. Estimated 2C DNA contents in these taxa range from 0.7-1.4 pg in the family Dasycladaceae and from 0.9-2.4 pg in the family Acetabulariaceae. In both families, species exhibiting characteristics considered to be primitive appear to have 2C DNA contents that approximate 50% of values found in species exhibiting characteristics considered to be more advanced. Results suggest that polyploidy events have accompanied evolution in the order but apparently have been infrequent and conservatively preserved, leading to a narrow range of relatively small genome sizes. Limitations on genome size increase are discussed in terms of constraints imposed by a prolonged uninucleate stage. Interspecific comparisons of genome size and gametangium volume suggest an inverse relationship. Gametangium volume appears to have phylogentic significance, in that taxa with more advanced characteristics generally have smaller gametangia.
The floristic relationships of the South African red algae have been evaluated by analyzing the distribution of more than 300 species found in Namibia, the West Cape, the East Cape and Natal in comparison with the species of other climatically determined biogeographic regions. Determinations of species’ affinities are based primarily on an assessment of shared advanced morphological traits. Over 60% of the red algal species of Namibia and the West Cape have their closest relationships with species occurring in the temperate floras of southern Australia, Tasmania and New Zealand or South America. The primary affinity of the East Cape and Natal floras is with the tropical flora of the Indian Ocean, but this region also includes major components related to species occurring in west and south Australia or Japan. It is concluded that the Rhodophytan flora of South Africa was assembled in response to paleoceanographic events and associated climatic changes that took place in the latter half of the Cenozoic and that the flora reached its present structure and species composition in late Oligocene and Miocene.
Distribution data on a world-wide scale of 613 red algal genera occurring in 22 climatically defined coastal regions were analysed with correspondence analysis (with detrending, with and without downweighting of rare genera). In the ordinations a climatic trend and a latitudinal trend could be readily distinguished. Distinct groups of regions could be identified by means of genera-by-region plots of the ordination with downweighting of rare genera. Two directed graphs illustrating nearest neighbour relationships and close neighbour relationships between the regions, respectively, were based on an asymmetrical coefficient of association. In the directed graphs overlapping relations between the regions are apparent. These results and possible explanations can be summarized as follows: A warm temperate to tropical group of regions (including all four tropical regions, three warm temperate regions in the Northern Hemisphere, and one warm temperate region in the Southern Hemisphere) possibly represents a formerly continuous Tethyan flora. Long range dispersal and Gondwanaland connections are possible modes of origin of a disjunct group of temperate regions in the Southern Hemisphere, including southern Australia, New Zealand and southern Africa. The warm temperate SE Pacific region is related to the warm temperate NE Pacific and SW Pacific regions. Its depauperate nature is possibly due to the El Nino’ phenomenon. The Antarctic region and the cold temperate regions of the Pacific and Atlantic coasts of South America and the subantarctic islands form a distinct cluster in all the analyses. The separateness of the temperate Pacific and Atlantic floras in the Northern Hemisphere contrasts with the relatedness of the Southern Hemisphere temperate floras. This separateness is ascribed to their long separation by the Bering Land Bridge (up into Pliocene, 2.106y).
Mediterranean marine biodiversity has received only a fraction of the attention accorded to its terrestrial counterpart, despite the great cultural and economic importance that the sea has been having for the Mediterranean countries. A rough estimate of more than 8500 species of macroscopic marine organisms should live in the Mediterranean Sea, corresponding to somewhat between 4% and 18% of the world marine species. This is a conspicuous figure if one considers that the Mediterranean Sea is only 0.82% in surface area and 0.32% in volume as compared to the world ocean. The high biodiversity of the Mediterranean Sea may be explained by historical (its tradition of study dates older than for almost any other sea), paleogeographic (its tormented geological history through the last 5 my has been determining the occurrence of distinct biogeographic categories), and ecological (its variety of climatic and hydrologic situations within a single basin has probably no equals in the world) reasons. Present-day Mediterranean biodiversity is undergoing rapid alteration under the combined pressure of climate change and human impact, but protection measures, either for species or ecosystems, are still scarce. To understand the role and patterns of Mediterranean marine biodiversity, marine ecological research should: first, re-value those scientific areas currently unfashionable with funding agencies (systematics, biogeography and taxonomy); second, start monitoring biodiversity with a long-term approach at a whole Mediterranean scale, possibly through an internationally co-ordinated network of marine protected areas.
The first English description of Halimeda was given by Parkinson in the 1640s. He called it Opuntia marina (the sea garland) and captured the essence of the species then known as “H. tuna” of the Mediterranean. The discovery of other species, in the intervening years, has shown that the genus is not always dainty, and the descriptive terminology has grown accordingly. The overall appearance of the genus is characteristic. It can be identified almost at once because it looks like some form of underwater cactus, with photosynthetic portions consisting of a series of calcified segments or joints, the strung leaves of Parkinson, which may be arranged in some branching pattern. The plant body, or Thallus, also possesses a holdfast that provides attachment to or in the substrate. This chapter explains the structure and composition of this cellulose free plant and summarizes the unusual structure and chemistry of Halimeda. It outlines the history of Halimeda studies, discoveries, various old and modern taxonomies, the culture procedures for field and laboratory, its growth and calcification, reproduction, biogeography, and phylogeny and productivity. The chapter also discusses the distribution of Halimeda in two reef systems: The Glory Be Reef and the Enewetak Atoll.
The genus Halimeda (Order Bryopsidales) is an important contributor of calcareous sediments to present day reefs. By ∼80 million years ago the genus appeared to have achieved limited distribution in both Old and New Worlds; today its 33 extant species are widely distributed throughout the tropics. Halimediform genera of the Ordovician exhibit considerable morphological similarity to the modern genus. However, the first records of Halimeda fossils appear to be Permian, with the greatest pre-Cenozoic species diversity being achieved during the latter part of the Cretaceous. The long paleohistory is capped by an apparent burst of speciation associated with the Holocene. At least three time periods during the ca. 260Mya of Halimeda history are likely to have had major impacts on evolution of the genus: (1) Cretaceous-Tertiary boundary events; (2) closing of the circumtropical Tethyan seaway with associated Messinian crisis; and (3) final closure of the Panama seaway. However, little concerning the relationship of these events to Halimeda phylogeny can be gleaned from its recorded paleohistory. The first strong phylogenetic data for the genus, provided by cladistic analyses of 18sDNA sequences, identify principal lineages corresponding to the three major taxonomic sections (Rhipsalis, Opuntia and Halimeda). These lineages provide the major axes of a proto phylogeny, and represent an apparent differentiation of the genus into at least 3 basic thallus designs. The most complex of the phylogenetic trees presented also indicates a geographic separation of rhipsalian species into Atlantic and Pacific clades. It is likely that these two major events occurred during the Cenozoic, with the second associated with a vicariant event such as the cessation of the circumglobal Tethys current. Research by paleontologists is especially needed for developing time references for major evolutionary events which will lead to setting an evolutionary clock for Halimeda independent of molecular data. Paleontologists also have an important role to play in testing the hypothesis that the burst of speciation in the Holocene is an artifact of differential collection, differential preservation or both, and that some of this speciation occurred in preceeding epochs. Investigation of these hypotheses, coupled with better samples, will reveal much more of the history of the genus during the period of its greatest success, the Cenozoic.
The inferred positions of global paleoshorelines through the 240 million
years of the Mesozoic and Cenozoic are presented within this atlas.
Thirty-one maps, generally corresponding to stratigraphic stages,
provide a snapshot of the continents and their shorelines at
approximately 8 million year intervals. The maps provide a
representation of the gross changes in the distribution of land and sea
throughout the Mesozoic and Cenozoic plotted on Mollweide projections of
paleocontinental reconstruction. They do not distinguish between well
and poorly defined shorelines, but the information sources are set out
in a bibliography numbering more than 2000 primary paleographic
references. This is a global compilation that presents the first attempt
at delineating global shorelines at stage level, and which represents
many years of work sponsored by British Petroleum International (BPI),
and work by BPI themselves between 1981 and 1987.
Grateloupia filicina (C. Agardh) Lamouroux, originally described from the Mediterranean Sea, has long been considered a textbook example of a marine red alga with a cosmopolitan distribution. An rbcL-based molecular phylogeny, encompassing samples covering the entire geographic distribution of the species, revealed a plethora of ‘‘cryptic’’ species, whereby the presence of genuine G. filicina is limited to the Mediterranean basin. The phylogeny revealed a strong biogeographic imprint, with specimens from temperate regions resolved in clades composed of species inhabiting the same geographic region. Presence of widely divergent morphologies in the temperate clades indicated that several lineages have converged independently to a G. filicina-type morphology. Tropical representatives are resolved in a single clade with very uniform G. filicina-type morphology and pairwise sequence divergences that are lower than the average divergence observed in temperate lineages. This, combined with a lack of clear geographic structure among the tropical lineages, may indicate a more recent divergence with long-range dispersal capacities. Violations to the biogeographic signal in temperate lineages seemed to be due to either inadequate taxonomy or recent introductions. Grateloupia minima P. & H. Crouan, a taxon placed in
synonymy under G. filicina, is reinstated as a separate species distributed in the northeast Atlantic
Ocean. Grateloupia capensis sp. nov. is described to accommodate specimens from South Africa with a G. filicina-type morphology, and G. filicina var. luxurians is elevated to species status. Morphological and anatomical characters were put forward that support the distinctiveness of these three distinct species.
Sibling species are common in all major marine groups and habitats. Their abundance reflects both inadequate study of morphological features of living organisms (''pseudo-sibling species'') and divergence in habitat, life history, and chemical recognition systems without parallel divergence in morphology. Many marine sibling species are quite distinct genetically. Others, however, exhibit slight genetic differences whose significance is only clear in sympatry and in combination with other subtle but concordant patterns of differentiation. A large number of abundant, well-studied, or economically important taxa have recently been shown to be complexes of sibling species. The broad habitat and geographic distributions characteristic of many marine species require reevaluation in this context.
Major hotspots of amphipod species richness and of species and generic endemicity can be recognized in shallow seas. Recognition of ‘hotspots’ for amphipods must take account of the species-area relationship but not of latitude. The richness and endemicity of amphipods in the Mediterranean Sea is shown to be high when compared with other shallow seas This indicates a long in situ evolutionary history and is therefore not compatible with the hypothesis that the Mediterranean fauna was extirpated in the late Miocene.
A phylogeny has been inferred from parsimony and likelihood analyses of plastid rbcL DNA sequences for seven recognized and six undescribed species of Gracilariopsis (Gp.) (Gracilariales, Rhodophyta). New descriptions and illustrations of cystocarp morphology are provided for four Gracilariopsis species from North and South America. The generitype, Gp. sjoestedtii (Kylin) Dawson, is reinstated to include plants distributed from British Columbia to Pacific Baja California, and the name is corrected to Gp. andersonii (Grunow) Dawson. Gracilariopsis lemaneiformis (Bory) Dawson, Acleto et Foldvik is shown not to have a worldwide distribution but to be restricted to the vicinity of Peru. Gracilariopsis costaricensis is recognized with the provision that it may prove to be conspecific with Gp. lemaneiformis. Gracilariopsis “lemaneiformis” from North and South Carolina is described as a new species, Gp. carolinensis Liao et Hommersand sp. nov. Gracilariopsis longissima (Gmelin) Steentoft, Irvine et Farnham from Western Europe and the Mediterranean Sea and Gp. tenuifrons (Bird et Oliveira) Fredericq et Hommersand from the Ca-ribbean Sea and Brazil are recognized. Entities that have been referred to Gp. “lemaneiformis” from China and Japan constitute an undescribed species that is related to Gp. heteroclada Zhang et Xia. An invasive species from the Gulf of California, Mexico, and South Australia that has been assigned to Gp. “lemaneiformis” is resolved in a clade that includes Gp. longissima. Four undescribed species are included in the molecular analyses. The systematics of Gracilariopsis is discussed in the light of the morphological and molecular evidence.
Numerous attempts to capture the morphological variability of the genus Caulerpa have resulted in an unstable classification of numerous varieties and formae. In the present study we attempted to test taxon boundaries by investigating morphological and genetic variation within and between seven taxa of Caulerpa, supposedly belonging to four species, sampled at different sites in a Philippine reef system. Using both field and culture observations, we described the relation between the variability of a set of morphological characters and ecological parameters, such as wave exposure, light intensity, and substrate type. Statistical analyses showed that the limits between two (out of three) ecads of the C. racemosa (Forsskål) J. Agardh complex were obscured by the presence of morphological plasticity. Other studied taxa of Caulerpa (i.e. C. cupressoides [Vahl] C. Agardh, C. serrulata [Forsskål] J. Agardh, and two formae of C. sertularioides [S. Gmelin] Howe) could be grouped based on morphology despite the presence of morphological plasticity. Our results indicated a strong association between light intensity and several quantitative morphological variables. Genetic diversity of these taxa was assessed by partial sequencing chloroplast rbcL and tufA genes and the ycf10-chlB chloroplast spacer. In all phylogenetic analyses, C. serrulata, C. cupressoides, C. sertularioides, and the three ecads of C. racemosa emerged as distinct genetic units. Despite the presence of morphological plasticity and morphological convergence, a subset of morphological characters traditionally used in taxonomic delimitation still had sufficient discriminative power to recognize the terminal phylogenetic clades.
Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship. We work with the scholarly community to preserve their work and the materials they rely upon, and to build a common research platform that promotes the discovery and use of these resources. For more information about JSTOR, please contact support@jstor.org. Abstract. Studies in terrestrial systems suggest that long-distance propagule dispersal is important for landscape pattern and dynamics, but largely inconsequential for local demography. By contrast, in marine systems, dispersal at regional scales may drive local dynamics, because many species may have large mean dispersal distances. To assess var-iation in marine dispersal scales, we estimated mean dispersal distances from genetic iso-lation-by-distance slopes. Estimates ranged widely, from a few meters to hundreds of kilometers. Dispersal differed among taxonomic groups (macroalgae, invertebrates, and fish) and among species in different functional groups (e.g., producers and herbivores). Differences in dispersal scale have important implications for marine community dynamics, reserve design, responses to large-scale perturbations, and evolution of interacting species. To place genetic estimates of marine dispersal in context, we compared them to other measures of dispersal in the ocean and to estimates of dispersal on land. Maximum scales of dispersal by sedentary marine species exceeded maximum estimates of terrestrial plant dispersal by at least one to two orders of magnitude. Direct and genetic estimates of terrestrial plant dispersal were comparable to estimates of marine plant dispersal. Rates of marine macroalgal range expansion, however, far exceeded spread rates of terrestrial plants. Terrestrial plant spread rates were more similar to those of short-dispersing marine organ-isms that lack secondary dispersal by drifting adults. Genetic estimates of dispersal by different functional groups suggest that herbivores typically disperse much farther than their plant resources both on land and in the sea, although the timing, frequency, and consequences of dispersal may differ in the two systems. Terrestrial herbivores have more flexible dispersal behavior than marine organisms that disperse each generation by plank-tonic transport of larvae. Our results validate some long-standing views about the greater dispersal potential of species in the ocean, but also highlight the extreme heterogeneity in dispersal scale among marine species. As a result, development of a community perspective on marine connectivity will require consideration of multiple dispersal mechanisms and scales.
Molecular systematic studies have changed the face of algal taxonomy. Particularly at the species level, molecular phylogenetic research has revealed the inaccuracy of morphology-based taxonomy: Cryptic and pseudo-cryptic species were shown to exist within many morphologically conceived species. This study focused on section Rhipsalis of the green algal genus Halimeda. This section was known to contain cryptic diversity and to comprise species with overlapping morphological boundaries. In the present study, species diversity within the section and identity of individual specimens were assessed using ITS1–5.8S–ITS2 (nrDNA) and rps3 (cpDNA) sequence data. The sequences grouped in a number of clear-cut genotypic clusters that were considered species. The same specimens were subjected to morphometric analysis of external morphological and anatomical structures. Morphological differences between the genotypic cluster species were assessed using discriminant analysis. It was shown that significant morphological differences exist between genetically delineated species and that allocation of specimens to species on the basis of morphometric variables is nearly perfect. Anatomical characters yielded better results than external morphological characters. Two approaches were offered to allow future morphological identifications: a probabilistic approach based on classification functions of discriminant analyses and the classical approach of an identification key.
Genetic differentiation among geographic isolates of the pantropical to warm-temperate red alga Digenea simplex (Wulfen) C. Agardh was investigated using random amplified polymorphic DNA (RAPD) markers, crossing studies, and temperature tolerances experiments. Eleven isolates representing populations from the Caribbean, eastern Atlantic, and Indo-West Pacific were compared. RAPD analysis clearly revealed an Indo-West Pacific group, a Caribbean/Cape Verde Islands group, and a Canary Islands group. Crossing studies showed different levels of inter fertility. In most crosses between Western Australian and Atlantic isolates, no hybrid tetrasporophytes were formed. In crosses between Caribbean and Cape Verde Islands isolates, tetrasporophytes developed, but the viability of tetraspores was reduced. Full sexual compatibility was observed among Cape Verde Islands isolates and among isolates from Bonaire. Temperature tolerance studies indicate that Pacific isolates have a broader temperature survival range than Atlantic isolates, which may be correlated to local temperature extremes. Despite the reduced level of sexual compatibility between Caribbean and Cape Verde Islands isolates, their shared position in the RAPD analysis and similar temperature responses suggest trans-Atlantic dispersal in the near geological past. In addition to their discrete position in the RAPD distance analysis, the Canary Islands isolates were significantly more cold-tolerant than the other Atlantic isolates. This finding is consistent with the hypothesis that the Canary Islands were recolonized from cold-adapted eastern Mediterranean populations after the last Pleistocene glaciation.
Recent field observations of highly organized, species- and sex-specific patterns of synchronous gamete release by tropical green algae (Bryopsidales) invite a variety of future studies into the ecology and life histories of an important component of tropical reef communities. This paper details sexual reproduction by 22 algal species within five common genera (Caulerpa, Halimeda, Penicillus, Rhipocephalus, and Udotea), including field observations on the spatial occurrence, timing, and color changes associated with fertility, data on gamete size and behavior, and descriptions of coincident changes in local species abundances. Ecologically ephemeral episodes of sexual reproduction involved macroscopic changes that reliably indicated developmental state and sexual identity. The time from onset of fertility to gamete release was 36 h (Halimeda), 48 h (Caulerpa, Penicillus, and Rhipocephalus), or 96 h (Udotea). All species produced flagellated, negatively buoyant, anisogamous gametes. Microgametes of all species were similar in size; however, considerable species-specific differences were seen in the size of macrogametes. In Caulerpa, Halimeda, and Udotea flabellum (Ellis and Solander) Lamouroux, the volumetric ratio of macrogametes to microgametes ranged from 2:1 to 45: 1, whereas more extreme levels of anisogamy (104: 1) were observed for Penicillus spp., Rhipocephalus phoenix (Ellis and Solander) Kuetzing, and other Udotea spp. The macrogametes of Caulerpa and Halimeda showed strong positive phototaxis. Although only a subset (generally about 5%) of the thalli representing each species released gametes on a given morning, most species underwent bouts of sexual reproduction on numerous occasions during the seasonal peak of reproductive activity (March–May). As might be expected for holocarpic species, dramatic declines in local algal abundance coincided with these periods. The density of sand-dwelling genera such as Penicillus fell by 80– 90% during this 3-month period in 1997. Similar declines in the cover of sprawling species such as Caulerpa racemosa ((Forsskal) J. Agardh) exposed large (35–50 m2) sections of previously overgrown reef substrate.
The section Opuntia within the green seaweed genus Halimeda includes sprawling and pendant thalli composed of strongly calcified segments. Within this section, identification of Atlantic material is straightforward, but Indo-Pacific material is often difficult to key out. This is particularly true for specimens resembling H. opuntia, H. distorta, and H. hederacea; many specimens do not fit any type or are morphologically intermediate. The goals of the present study are to define morphologically and genetically distinct groups among such specimens and to assess phylogeographic patterns within these groups. Specimens were collected throughout the geographical and morphological range. Sequences of H. minima and H. gracilis were included as outgroups. Two morphological groups were discerned within the ingroup; the first fit H. opuntia, whereas most specimens in the second group, referred to as the distorta–hederacea complex, did not fit any species description unambiguously. The latter were subdivided into two subgroups corresponding more or less to H. hederacea and H. distorta, yet intermediates between these morphs existed. A phylogeny inferred from partial nuclear rDNA sequences showed one lineage with H. opuntia and a second one containing the distorta–hederacea complex, thus corroborating the two major morphological groups. The distorta–hederacea complex contained two clades that show only partial correspondence with the morphological subgroups. Therefore, H. hederacea is synonymized with H. distorta. Phylogeographic structure within H. opuntia indicated that this species dispersed from the Indo-Pacific into the Atlantic. Fossil records of the species also show occurrence at Pacific sites throughout the last 105 years and a sudden appearance in the Caribbean and Bahamas during the last millennium.
Morphological data has provided a basis for the hypothesis that three taxa belonging to the Caulerpa racemosa complex occur in the Mediterranean Sea: var. turbinata–uvifera, var. lamourouxi, and the `invasive variety'. In order to test this hypothesis and to determine the origin of the `invasive variety', the transcribed spacer ITS1–ITS2 and an 18S ribosomal DNA (rDNA) intron were analysed from 16 isolates of Caulerpa racemosa. The `invasive variety' shows intraindividual polymorphism for both types of sequences. The ITS1–ITS2 data confirm that the three morphological varieties of C. racemosa from the Mediterranean Sea are distinct taxonomic units. The 18S intron data suggest that the new `invasive variety' could be a recent hybrid between var. turbinata–uvifera and an unknown tropical strain. Incongruence between the phylogenetic tree computed from ITS1–ITS2 regions and the 18S intron indicates that homogenization processes of concerted evolution have run at different rates.
Seventeen species of Halimeda have been grown in the laboratory in an open-circuit seawater cascade during a 6 year period. All but one grew vegetatively (generated new segments) to some extent and several species grew luxuriantly. A few species also reproduced vegetatively by developing new plants at the ends of fine runners. However, most significant was the production of gametangia by all the species in the cascade whilst several of those species, plus one not grown in the cascade, were also observed fertile in the field. Different material from a single collection sometimes became fertile in the cascade in successive years and then often at very similar times, suggesting a distinct seasonality and response to environmental stimuli. Some lunar periodicity was also detected in the fertility of three species. Species-specific differences in the structure of gametangial clusters, particularly the size of the gametangia, were observed. In all species examined, gametophore branches ended in unexpanded tips which often had a distinct, thickened cap. Upon maturity, the contents of all the gametangia in a cluster were explosively released through these discharge papillae. This release usually commenced only 5 to 15 minutes after the plants were re-illuminated on the day following the appearance of gametangia although two species, H. incrassata and H. melanesica, often released their gametes in the late afternoon.
Twenty-one molecular genetic studies of thirteen antitropical Pacific fishes are herein reviewed. High dispersal potentials and Plio-Pleistocene transequatorial divergence are suggested for approximately half of the taxa studied, consistent with movement across the tropics during glacial periods. Divergences within two fish groups were mid-Miocene in age, corresponding to a period suggested for vicariant isolation associated with equatorial warming, but high dispersal potentials complicate the interpretation of biogeographic history. Only one study suggested transequatorial divergence older than 20 million years. There is a greater proportion of Pleistocene transequatorial divergences in the East Pacific than the West Pacific, consistent with the suggestion that conditions in the East Pacific are more amenable to the formation of antitropical distributions. Multiple transequatorial divergences have been observed within at least two groups, and instances of cryptic speciation have been identified twice. Areas for future research concern taxa that differ from the majority studied to date with respect to latitudinal distribution, bathymetry, evolutionary age, and dispersal potential. Molecular characters have demonstrated utility for the study of antitropical fishes, but with limitations.
Partial 18S rDNA sequences, including a 102 base pair insertion, were used to infer a phylogeny among 48 samples across all sections in Halimeda Lamouroux, 1812. The phylogeny reveals a separation of the monophyletic section Rhipsalis into a western Atlantic and a western Pacific clade. Consequently, morphologically similar species within this section such as H. monile (Ellis & Solander) Lamouroux (western Atlantic), and H. cylindracea Decaisne (western Pacific), are not sister taxa. Vicariant events that separated the tropical regions of the Atlantic and Indo-Pacific Oceans can explain the observed biogeographical pattern in section Rhipsalis.