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Postglacial dispersal, glacial refugia, and clonal structure in Russian/Siberian populations of the arctic Daphnia pulex complex
Abstract
Results from an extensive allozymic survey of the genetic (clonal) structure of Russian/Siberian populations in the arctic Daphnia pulex complex yielded high clonal diversity/richness estimates, at both the intrapopulational and intraregional levels. Highest levels of clonal diversity were detected in the heart of the Beringian glacial refuge, with lower levels detected in glaciated regions (western Russia). mtDNA haplotype diversity (based on RFLPs) showed similar spatial trends, with the highest levels of haplotype diversity again being found in Beringia. Several haplotypes were extremely widespread (in the order of thousands of kilometres across the breadth of Eurasia), and evidence for presumed mutationally derived haplotypes was plentiful. Spatial autocorrelation analysis revealed a significant clinal pattern in the degree of genetic similarity among mtDNA haplotypes. In addition, similarity of clonal arrays (based on allozymes) showed a significant inverse association with geographical distance; i.e. similarity of clonal arrays between populations increased with decreasing geographical distance between populations. Sporadic sexual reproduction (based on Hardy–Weinberg expectations) was detected in Beringia, and has undoubtedly played a role in fuelling the production of novel genotypes. Our results suggest that vast expanses of northern Eurasia have been colonized by a small number of geographically widespread haplotypes, with more regionally restricted haplotypes constituting the remaining lineages. We discuss our results within the general framework of biogeographical colonization events of the Arctic by members of the D. pulex complex, and place these data into the broader picture of the importance of Beringia as a glacial refuge for many taxa during the Pleistocene.Keywords: allozymes, Beringia, Daphnia, glacial refugia, mtDNA, phylogeography
... The present study extends this result by discovering the presence of a diagnostic substitution at APK, and together with other loci verifying the absence of hybrids between these species in mid-Europe. However, the APK heterozygotes often have been found in obligatory asexual populations of the D. pulex and D. tenebrosa complex from arctic and subarctic regions of Eurasia, from which many clones are thought to be of multiple hybrid origin (Weider and Hobaek 1997). Our further results indicate that such arctic hybrids persist even in the temperate regions of Central Europe as glacial relicts . ...
... Indeed there is an uncertainty that derives from the failure of this study to survey populations across the Palearctic. As a result, it might be possible that European and North American populations are linked by genetic intermediates in Asia that might be suggested by occurrence of several common mtDNA D. pulex haplotypes across nothern Eurasia (Weider and Hobaek 1997). On the other hand, it seems clearly to be inappropriate to neglect the likelihood that important biological differences are associated with this gene pool divergence. ...
... Finally, tests of reproductive isolation-in cases of allopatry-would be particularly useful. The detailed analysis of faunas in contact zones between Eurasia and North America, such as Beringia, that has been already started by Weider and Hobaek (1997) seems to be particularly useful. Finally, given their amenability to experimental analysis, breeding tests could examine the fitness of both F 1 and advanced generation hybrids between lineages from different continents. ...
The species overlap between European and North American cladoceran faunas has been questioned from the very beginning of faunistic studies on Nearctic zooplankton and still remains unsettled. However, more recently, genetic techniques seem to overcome the limits of morphology as the basis for taxonomy. We analyzed 8-11 allozyme loci to assess the genetic differentiation between intercontinental counterparts of four daphniids: Daphnia curvirostris, Daphnia obtusa, Daphnia pulex, and Daphnia pulicaria. Despite their morphological likeness, all equivalents showed a large amount of genetic divergence between continents due to complete allelic substitutions and major gene frequency shifts. From an evolutionary perspective, this study shows that as in other organisms, geographic isolation seems to be sufficient to minimize gene flow to levels at which the origin of new daphniid species can be considered. From a practical point of view, a revision of Holarctic daphniid taxonomy should be considered.
... Clustering analysis of microsatellite data for the same specimens used for Rab4 sequencing placed TEN genotypes in a group with EPC, but did not provide clear evidence of clustering of NAPC with any other species [23]. Daphnia tenebrosa is an Arctic species reproducing almost exclusively by obligate parthenogenesis [25], distributed in the Arctic of both North America and Eurasia (Figure 1), and its low mtDNA divergence from EPC might be interpreted as a recent origin of the European populations from an Arctic (e.g. Beringian) ancestor [21], while the European D. pulex (EPX) is thought to be a long-diverged species with no signatures of gene flow with other species [26]. ...
... A recent study identified two amino acid differences between the polypeptides encoded by F allele versus S allele, although their functional significance has not as yet been demonstrated [24]. Interestingly, allozyme surveys in the Arctic detected F allele in various populations of D. tenebrosa [25,28], and SF heterozygotes have been reported from D. pulicaria from mountain lakes in Europe [29]. Shared allozymes between the 'tenebrosa group' and 'Pulicaria group' were interpreted as an introgression [30], but as yet no DNA sequence has been obtained for F allele from D. tenebrosa or European D. pulicaria [24]. ...
... The method infers the species tree from multiple genes sampled from multiple individuals of each species [31]. We did not include D. tenebrosa because it reproduces almost exclusively asexually throughout its distribution [25,28], violating the *BEAST assumption of recombination between loci [31]. Temperate populations of D. pulex from western North America and temperate eastern populations of D. pulicaria reproduce by cyclical parthenogenesis (series of asexual generations interrupted by a sexual generation [49]), and since many of the samples in our study were from these populations, we considered that in these species and on the time scale relevant for the coalescent analysis, the loci can be considered effectively independent. ...
The North American ecological species Daphniapulicaria and Daphniapulex are thought to have diverged from a common ancestor by adaptation to sympatric but ecologically distinct lake and pond habitats respectively. Based on mtDNA relationships, European D. pulicaria is considered a different species only distantly related to its North American counterpart, but both species share a lactate dehydrogenase (Ldh) allele F supposedly involved in lake adaptation in North America, and the same allele is also carried by the related Holarctic Daphniatenebrosa. The correct inference of the species' ancestral relationships is therefore critical for understanding the origin of their adaptive divergence. Our species tree inferred from unlinked nuclear loci for D. pulicaria and D. pulex resolved the European and North American D. pulicaria as sister clades, and we argue that the discordant mtDNA gene tree is best explained by capture of D. pulex mtDNA by D. pulicaria in North America. The Ldh gene tree shows that F-class alleles in D. pulicaria and D. tenebrosa are due to common descent (as opposed to introgression), with D. tenebrosa alleles paraphyletic with respect to D. pulicaria alleles. That D. tenebrosa still segregates the ancestral and derived amino acids at the two sites distinguishing the pond and lake alleles suggests that D. pulicaria inherited the derived states from the D. tenebrosa ancestry. Our results suggest that some adaptations restricting the gene flow between D. pulicaria and D. pulex might have evolved in response to selection in ancestral environments rather than in the species' current sympatric habitats. The Arctic (D. tenebrosa) populations are likely to provide important clues about these issues.
... Studies on the distribution of multilocus genotypes tracking particular obligately parthenogenetic clones indicate that single lineages can have distributions covering many ponds and distances over 1000 km (Weider and Hobaek, 1997;Weider et al., 1996Weider et al., , 1999b. Parthenogenetic ostracod clones have been found to be widespread in recently created farm ponds (Chaplin and Ayre, 1997). ...
... In obligately parthenogenetic zooplankton, patterns of population genetic differentiation are strikingly different from those characterized in cyclically parthenogenetic zooplankton. The occurrence and distribution of multilocus genotypes and mtDNA haplotypes have been extensively documented for several obligately parthenogenetic circumarctic Daphnia taxa by Weider and coworkers (Weider and Hobaek, 1997;Weider et al., 1996Weider et al., , 1999a. There is clear evidence that certain genotypes can become widespread, occupying areas covering distances of more than 1000 km. ...
... Studies on obligately asexual Daphnia reveal different phylogeographic patterns than those found in cyclically parthenogenetic taxa. Taxa of the circumarctic D. pulex complex co-occur and are found across large areas (Weider and Hobaek, 1997;Weider et al., 1999a, b). In addition, some haplotypes of D. tenebrosa have dispersed across immense geographic distances (Weider et al., 1999b). ...
Many aquatic organisms rely on passive transport of resting stages for their dispersal. In this review, we provide evidence pointing to the high dispersal capacity of both animals (cladocerans, rotifers and bryozoans) and aquatic macrophytes inhabiting lentic habitats. This evidence includes direct observation of dispersal by vectors such as wind and waterfowl and the rapid colonization of new habitats. Such high dispersal capacity contrasts with the abundant evidence of pronounced genetic differentiation among neighbouring populations in many pond-dwelling organisms. We provide an overview of the potential mechanisms causing a discrepancy between high dispersal rates and reduced levels of gene flow. We argue that founder events combined with rapid local adaptation may underlie the striking patterns of genetic differentiation for neutral markers in many aquatic organisms. Rapid population growth and local adaptation upon colonization of a new habitat result in the effective monopolization of resources, yielding a strong priority effect. Once a population is locally adapted, the presence of a large resting propagule bank provides a powerful buffer against newly invading genotypes, so enhancing priority effects. Under this Monopolization Hypothesis, high genetic differentiation among nearby populations largely reflects founder events. Phylogeographic data support a scenario of low effective dispersal among populations and persistent effects of historical colonization in cyclical parthenogens. A comparison of patterns of gene flow in taxa with different life cycles suggests an important role of local adaptation in reducing gene flow among populations. We argue that patterns of regional genetic differentiation may often reflect historical colonization of new habitats rather than contemporary gene flow.
... These results indicate that for the pulicaria group, clonal arrays were more similar in composition between regions that were in closer proximity than those arrays found at greater distances from each other. This suggests some differential movement/dispersion of clones, as noted previously by Weider & Hobaek (1997) in the arctic Daphnia pulex complex from Siberia/Russia. Owing to the small number of regions where tenebrosa group clones were detected and the complete absence of any shared clones between regions, a similar analysis could not be conducted. ...
... However, there were a couple of populations (i.e. one each from regions 6 and 9; Fig. 1), which exhibited high intrapopulational clonal richness, and which did not exhibit any significant deviations from HWE expected genotype frequencies. Although no males were detected in these populations, these data suggest that some sporadic sexual reproduction may be occurring in certain regions (i.e. in or near Beringia, regions 1, 2, and 4), as suggested by previous arctic studies of this species complex (Weider & Hobaek 1997;Weider et al. 1999b), as well as sporadic sexual populations in the central Canadian Low Arctic (regions 6 and 9, Fig. 1). However, the genetic (allozyme) data for the vast majority of populations surveyed in this study indicate that the primary mode of reproduction is via obligate parthenogenesis across much of the Canadian Arctic, as shown previously (Weider et al. , 1999b. ...
... Beringia) harbouring high levels of genetic variation, a result strikingly similar to our results. Examples of elevated levels of genetic variation in taxa found in the Beringian glacial refuge (Quinn 1992;Bernatchez & Dodson 1994;Bernatchez & Wilson 1998;Ehrich et al. 2000), including primarily clonal (asexual) organisms (Weider & Hobaek 1997;Weider et al. 1999a,b;Stenström et al. 2001), are not uncommon, when compared with populations outside the refugium, but such a relationship is not universal (Fedorov et al. 1999;Ehrich et al. 2000). ...
As part of a large international Arctic biodiversity expedition (Tundra Northwest '99), we examined the distribution of members of the arctic Daphnia pulex complex (Cladocera, Anomopoda) from 121 tundra ponds, spread across 16 sites spanning a large portion of arctic Canada (i.e. from 62 degrees 22' N to 79 degrees 01' N; 66 degrees 45' W to 139 degrees 37' W). Using allozyme electrophoresis and mitochondrial (mt)DNA analyses, we examined the population genetic (clonal) structure of these populations. The following taxa were detected in this complex: Daphnia pulicaria, D. middendorffiana and D. tenebrosa. Clear geographical differences in mean clonal richness and diversity were observed, with most western sites exhibiting higher clonal richness and diversity, than sites in the eastern Canadian Arctic. For both the pulicaria group (i.e. D. pulicaria and D. middendorffiana) and D. tenebrosa, the highest mean regional clonal richness was detected from the southern section of Banks Island, an unglaciated site situated on the edge or directly in the eastern fringe of the Beringian glacial refuge. A significant negative correlation was found between geographical distance from the Beringian edge, and overall regional clonal richness (i.e. sites closer to the edge harboured greater clonal richness). These results clearly indicate that more recently deglaciated regions (i.e. eastern Canadian Arctic) harbour lower levels of clonal richness than western regions nearer Beringia. We discuss the role that glacial refugia have played in influencing both biotic and genetic diversity in arctic taxa.
... This species complex shows geographic parthenogenesis, with populations in warm and cold temperate zones being cyclically parthenogenetic, while the high Arctic is dominated by asexual lineages: Daphnia pulicaria and D. middendorffiana (Decaestecker, De Meester & Mergeay 2009). The landscape genetic structure of obligately parthenogenetic species in the high Arctic has been extensively examined in earlier studies, which have reported both widespread occurrence of specific haplotypes, as well as co-occurrence of multiple clones in single habitats (Ward et al. 1994;Weider & Hobak 1997;Weider & Hobaek 2003). Typically, ponds were found to be inhabited by 1-6 clones (Ward et al. 1994;Weider et al. 1996). ...
... This is in concordance with previous circum-Arctic studies where occurrence of triploid and tetraploid clones of the Daphnia pulex spp. complex has been reported based on allozymes (Ward et al. 1994;Dufresne & Hebert 1995;Weider et al. 1996Weider et al. , 1999aWeider & Hobak 1997;Weider & Hobaek 2003) and genome size investigations (Dufresne & Hebert 1995;Vergilino, Belzile & Dufresne 2009). Polyploid asexual D. pulex complex taxa have also been reported in the Daphnia pulex spp. ...
1. Due to climate change, Arctic ice sheets are retreating. This leads to the
formation of numerous new periglacial ponds and lakes, which are being
colonized by planktonic organisms such as the water flea Daphnia. This system
provides unique opportunities to test genotype colonization dynamics and the
genetic assemblage of populations. Here, we studied clonal richness of the
Daphnia pulex species complex in novel periglacial habitats created by glacial
retreat in the Jakobshavn Isbræ area of western Greenland.
2. Along a 10 km transect, we surveyed 73 periglacial habitats out of which 61
were colonized by Daphnia pulex. Hence for our analysis we used 21 ponds and
40 lakes in two clusters of habitats differing in age (estimated <50 years versus
>150 years). We tested the expectation that genetic diversity would be low in
recently-formed (i.e., young), small habitats, but would increase with increasing
age and size.
3. We identified a total of 42 genetically-distinct clones belonging to two obligately
asexual species of the D. pulex species complex: D. middendorffiana and the
much more abundant D. pulicaria. While regional clonal richness was high, most
Accepted Article This article is protected by copyright. All rights reserved.
clones were rare: 16 clones were restricted to a single habitat and the five most
widespread clones accounted for 68% of all individuals sampled. On average 3.2
clones (range: 1-12) coexisted in a given pond or lake. There was no relationship
between clonal richness and habitat size when we controlled for habitat age.
Whereas clonal richness was statistically higher in the cluster of older habitats
when compared with the cluster of younger ponds and lakes, most young
habitats were colonized by multiple genotypes.
4. Our data suggest that newly-formed (periglacial) ponds and lakes are within
decades colonized by multiple genotypes via multiple colonization events, even
in the smallest of our study systems (4 m2).
... Localities that have been recently colonized are likely to have decreased genetic diversity relative to the source population, as only a subset of the alleles will be carried by colonizing individuals. This concept has been supported both empirically (Templeton et al. 1995;Hewitt 1996;Merila et al. 1997;Weider and Hobaek 1997;Bernatchez and Wilson 1998;McCusker et al. 2000) and theoretically (Templeton et al. 1995;Hewitt 1996;Weider and Hobaek 1997). Based on this concept, we can predict shorter species presence to the north, and extended presence of ancestral populations to the south. ...
... Localities that have been recently colonized are likely to have decreased genetic diversity relative to the source population, as only a subset of the alleles will be carried by colonizing individuals. This concept has been supported both empirically (Templeton et al. 1995;Hewitt 1996;Merila et al. 1997;Weider and Hobaek 1997;Bernatchez and Wilson 1998;McCusker et al. 2000) and theoretically (Templeton et al. 1995;Hewitt 1996;Weider and Hobaek 1997). Based on this concept, we can predict shorter species presence to the north, and extended presence of ancestral populations to the south. ...
The genetic variation of many species in the Northern Hemisphere has been influenced by climatic changes during the Pleistocene Epoch. Phylogeographic studies can help determine intraspecific relationships and postglacial recolonization routes for many of these species, potentially leading to a more complete understanding of how flora and fauna respond to dramatic climate change. We analyzed the variation in the mitochondrial DNA sequences of Chinook salmon Oncorhynchus tshawytscha from California to the Kamchatka Peninsula, Russia, to gain insight into the role of Pleistocene glaciation in the genetic structuring of this species. The geographic distribution of haplotypes revealed high levels of genetic diversity in the Columbia River drainage. Nested clade analysis suggests northward expansion from this area during the late Pleistocene, a hypothesis that is further supported by evidence of demographic growth and population expansion in the northern portion of the species' range. Estimates of the divergence time between two phylogenetic clades are correlated with interglacial periods of the Pleistocene. The data suggest the absence of Chinook salmon from the current northern part of its distribution until the late Pleistocene, when northward expansion from a southern refugium occurred (during an interglacial period), followed by the recent genetic divergence of these northern populations.
... The distribution of genetic lineages within North American populations of the cladoceran Daphnia laevis is roughly concordant with three major waterfowl flyways (Taylor et al. 1998). Similar agreement between mitochondrial haplotype distribution and waterfowl migratory routes suggests that waterfowl have played an important role in the postglacial expansion of Daphnia pulex in Greenland and Iceland (Weider et al. 1996), and Beringia (Weider & Hobaek 1997). ...
... For example, range extensions of freshwater taxa at the end of the last ice age may have introduced multiple genetic lineages into individual lakes and ponds (Stemberger 1995), and such historical events may not be readily distinguishable from ongoing gene flow without the use of rapidly evolving molecular markers (Freeland et al. 2000c). Notably few studies have used mitochondrial DNA data to infer historical patterns of range expansion and dispersal in freshwater invertebrates (Avise 2000; but see Bilton 1994, Nürnberger & Harrison 1995, Meyran et al. 1997, Weider & Hobaek 1997. Disentangling the extent to which population structure results from recurrent forces, such as gene flow, versus historical events, such as fragmentation and range expansion, will be crucial to understanding the frequency of dispersal in freshwater taxa. ...
... The distribution of genetic lineages within North American populations of the cladoceran Daphnia laevis is roughly concordant with three major waterfowl flyways (Taylor et al. 1998). Similar agreement between mitochondrial haplotype distribution and waterfowl migratory routes suggests that waterfowl have played an important role in the postglacial expansion of Daphnia pulex in Greenland and Iceland (Weider et al. 1996), and Beringia (Weider & Hobaek 1997). Although waterfowl migrations apparently play at least an occasional role in the dispersal of freshwater zooplankton and bryozoans, there are several reasons why it will be difficult to fully determine the extent that waterfowl link sites through genetic studies. ...
... For example, range extensions of freshwater taxa at the end of the last ice age may have introduced multiple genetic lineages into individual lakes and ponds (Stemberger 1995), and such historical events may not be readily distinguishable from ongoing gene flow without the use of rapidly evolving molecular markers (Freeland et al. 2000c). Notably few studies have used mitochondrial DNA data to infer historical patterns of range expansion and dispersal in freshwater invertebrates (Avise 2000; but see Bilton 1994, Nürnberger & Harrison 1995, Meyran et al. 1997, Weider & Hobaek 1997). Disentangling the extent to which population structure results from recurrent forces, such as gene flow, versus historical events, such as fragmentation and range expansion, will be crucial to understanding the frequency of dispersal in freshwater taxa. ...
Movement between discrete habitat patches can present significant challenges to organisms. Freshwater invertebrates achieve dispersal using a variety of mechanisms that can be broadly categorized as active or passive, and which have important consequences for processes of colonization, gene flow, and evolutionary divergence. Apart from flight in adult freshwater insects, active dispersal appears relatively uncommon. Passive dispersal may occur through transport by animal vectors or wind, often involving a specific desiccation-resistant stage in the life cycle. Dispersal in freshwater taxa is difficult to study directly, and rare but biologically significant dispersal events may remain undetected. Increased use of molecular markers has provided considerable insight into the frequency of dispersal in freshwater invertebrates, particularly for groups such as crustaceans and bryozoans that disperse passively through the transport of desiccation-resistant propagules. The establishment of propagule banks in sediment promotes dispersal in time and may be particularly important for passive dispersers by allowing temporal escape from unfavorable conditions. Patterns that apply to dispersal in freshwater invertebrates can be readily extended to other freshwater taxa, since common challenges arise from the colonization of isolated aquatic systems.
... As mentioned above, species of the D. pulex complex are widely distributed in the arctic-subarctic water bodies of Eurasia and North America. D. middendorffiana and D. pulex are investigated studied using molecular genetic methods [40,41,[67][68][69][70][71]. The analysis of the variability of the mitochondrial DNA gene fragments (COI, ND4 and ND5) within the D. pulex complex allow the detection of four to 12 deeply divergent lineages, which were characterized by different demographic histories and origins [41]. ...
The variability of the 12S gene fragment of the mtDNA for taxa belonging to subgenus Daphnia (Daphnia) O.F. Müller, 1776 (Crustacea: Cladocera) in NE Russia is studied, and their phylogenetic analysis performed. We identified (based both on morphological and molecular data) nine species belonging to four species complexes, namely: (A) D. longispina s.l.: (1) D. longispina O.F. Müller, 1776; (2) D. dentifera Forbes, 1893; (3) D. galeata Sars, 1864; (4) D. umbra Taylor, Hebert et Colbourne, 1996; (B) D. cristata s.l.: (5) D. cristata Sars, 1862; (6) D. longiremis Sars, 1862; (C) D. curvirostris s.l.: (7) D. curvirostris Eylmann, 1887; (D) D. pulex s.l.: (8) D. pulex Leydig, 1860; (9) D. middendorffiana Fischer, 1851. Rare arcto-mountainous taxon D. umbra was found in the mountains of the Sakha (Yakutia) Republic for the first time. Species diversity in NE Asia is relatively low, and the most revealed taxa are trans-Beringian. We also performed a phylogeographic analysis of D. dentifera and D. pulex s.l., the two most common species in NE Russia. Our new data allow us to assume that the daphniids of NE Asia have undergone various evolutionary scenarios during the Pleistocene period: survival is within some local refugia, and re-colonization from these areas and from North America through the Beringian land bridge, etc. We agree with previous authors who revealed that the patterns in the studied species groups are relatively recent (of Late Pleistocene or even Holocene age), although the main phylogenetic daphniid lineages (mainly congruent with the biological species) are very old. Our results provide convincing evidence for the hypothesis that NE Russia is a very important source of modern haplotypic diversity for the cladocerans.
... All rights reserved species complex display a biogeographic pattern consistent with a shift to a high-Arctic refuge during the last glaciation event, likely due to northward movement via passive dispersal. Such events led to the colonization of parts of Greenland, Iceland, Svalbard, and northern Europe (Van Raay & Crease, 1995;Weider, Hobaek, Crease, & Stibor 1996;Weider & Hobaek, 1997;Colbourne et al., 1998;Weider et al., 1999a;Weider & Hobaek, 2003). Populations from glaciated regions typically show decreased genetic divergence compared to populations from unglaciated regions (Weider & Hobaek, 2003;Ishida & Taylor, 2007a). ...
The microcrustacean Daphnia is arguably one of the most studied zooplankton species, having a well understood ecology, life history, and a relatively well studied evolutionary history. Despite this wealth of knowledge, species boundaries within closely related species in this genus often remain elusive and the major evolutionary forces driving the diversity of daphniids remain controversial. This genus contains more than 80 species with multiple cryptic species complexes, with many closely related species able to hybridize. Here we review speciation research in Daphnia within the framework of current speciation theory. We evaluate the role of geography, ecology, and biology in restricting gene flow and promoting diversification. Of the 253 speciation studies on Daphnia, the majority of studies examine geographic barriers (55%). While evidence shows that geographic barriers play a role in species divergence, ecological barriers are also likely prominent in Daphnia speciation. We assess the contribution of ecological and non‐ecological reproductive isolating barriers between closely related species of Daphnia and found that none of the reproductive isolating barriers are restricting gene flow completely. Research on reproductive isolating barriers has disproportionally focused on two species complexes, the Daphnia pulex and Daphnia longispina species complexes. Lastly, we identify areas of research that remain relatively unexplored and discuss future research directions that build our understanding of speciation in daphniids.
... pulex species complex display a biogeographic pattern consistent with a shift to a high-Arctic refuge during the last glaciation event, likely due to northward movement via passive dispersal. This dispersal colonized parts of Greenland, Iceland, Svalbard, and northern Europe (Van Raay & Crease, 1995;Weider, Hobaek, Crease, & Stibor 1996;Weider & Hobaek, 1997;Colbourne et al., 1998;Weider et al., 1999a;Weider & Hobaek, 2003). Populations from glaciated regions typically show decreased genetic divergence compared to populations from unglaciated regions (Ishida & Taylor, 2007a). ...
... The intensive speciation here might be due to the presence of numerous isolated and environmentally different glacial refugia, ice-dammed lakes, and their periodical catastrophic outbursts causing extensive floodings, connections and disconnections of river basins, variability of recolonization routes, etc. (see Kvasov 1975;Hewitt 2000Hewitt , 2001Hewitt , 2004Mangerud et al. 2004). The same factors are known to be applicable to other Cladocera taxa, e.g., Daphnia (Weider & Hobaek 1997), Bosmina (Haney & Taylor 2003;Faustova et al. 2010Faustova et al. , 2011, and Limnosida (Korovchinsky 2014). ...
A new species of the genus Bythotrephes is described based on material collected in the mountain lakes of Tyva Republic (Southern Siberia, Russia). The representatives of the new species are especially close to those of B. longimanus having long tl I, straight caudal process, and only two pairs of claws on postabdomen and caudal process, respectively. At the same time, the new species is, on average, smaller with shorter caudal process and fairly long apical setae of second endopodital segment of the thoracic limbs of first pair (tl I). Supplemental data on morphology, taxonomy, and geographic distribution of other species of the genus, e.g., B. arcticus, B. cederströmii, B. brevimanus, and B. lilljeborgi, are presented. For B. cederströmii, in particular, females of first generation hatched from resting eggs are described for the first time. Classification of the genus is discussed and an updated key for species and a hybrid form is presented. The highest species richness of the genus, observed within the Scandinavian Peninsula and in the north of European Russia, may indicate the central region of primary speciation which generally coincides with the region of the last Quaternary maximum glaciation. The isolated occurrence of three species, B. longimanus, B. transcaucasicus, and B. centralasiaticus sp. nov. on the southern border of the genus’ range, in pre-Alpine and mountain lakes of Europe, Transcaucasia, and Southern Siberia (Tyva) and isolated localities of B. arcticus in Northern Kazakhstan, could also be due to the effect of glaciation(s). Regarding the origin of the genus Bythotrephes, it is hypothesized that it occurred in pre-Pleistocene time in the ancient Ponto-Caspian basin, experiencing large-scale transgressions, where the intensive radiation of ancestral Onychopoda probably took place.
... http://dx.doi.org/10.1101/334243 doi: bioRxiv preprint first posted online May. 30, 2018; Leibold 2010; Steiner et al. 2016), and has also been used to highlight colonisation processes after glaciation events (Weider and Hobaek 1997). Moreover, it may likewise have importance for informing the management of zooplankton invasions, such as that of the spread of Daphnia lumholtzi across North America (Dzialowski et al. 2000;Havel et al. 2002). ...
Dispersal is fundamental to population dynamics and it is increasingly apparent that most organisms make dispersal decisions based upon information gathered from the environment. Ideally, organisms would make fully informed decisions, with knowledge of both intra-patch conditions (conditions in their current location) and extra-patch conditions (conditions in alternative locations). Acquiring information is costly, however, and extra-patch information will typically be costlier to obtain than intra-patch information. As a consequence, theory suggests that organisms will often make partially informed dispersal decisions, utilising intra-patch information only. We test this proposition in an experimental two-patch system using populations of the aquatic crustacean, Daphnia carinata. We manipulated conditions (food availability) in the population's home patch, and in its alternative patch. We found that D. carinata made use of intra-patch information (resource limitation in the home patch induced a ten-fold increase in dispersal probability) but made no use of extra-patch information (resource limitation in the alternative patch did not affect dispersal probability). Our work highlights both the very large influence that information can have on dispersal probability, but also that dispersal decisions will often be made in only a partially informed manner.
... Our results show that quantitative estimates of waterfowl movements provided a better fit to genetic population structure than geographical distances for three of four invertebrate species, and this may explain previous studies reporting high levels of gene flow between invertebrate populations (Weider et al. 1996;Weider and Hobaek 1997;Taylor et al. 1998;Freeland et al. 2000). Furthermore, our results suggest that waterfowl transport propagules effectively during migration, or at least with enough frequency to affect genetic patterns of geographical variation in the transported species. ...
Waterfowl often have been assumed to disperse freshwater aquatic organisms between isolated wetlands, but no one has analyzed the impact of this transport on the population structure of aquatic organisms. For three cladocerans (Daphnia ambigua, Daphnia laevis, and Sida crystallina) and one bryozoan (Cristatella mucedo), we estimated the genetic distances between populations across North America using sequences of several mitochondrial DNA genes and genotypic frequencies at allozyme and microsatellite loci. Waterfowl movements across North America (estimated from band recovery data) explained a significant proportion of the gene flow occurring between populations across the continent for three of the four species, even after controlling for geographic distances between localities. The fourth species, S. crystallina, has propagules less likely to survive desiccation or ingestion by birds. Differences in the capacity to exploit bird‐mediated transport are likely to have important consequences for the ecology of aquatic communities and the spread of invasive species.
... The extensive glacial history of North America has played a major role in present day distributions and dispersal routes of freshwater fishes (Millette et al., 2011). Glacial range expansions and contractions lead to re-arrangements of water systems that gave rise to fragmented aquatic refugia (Weider & Hobaek, 1997). The greatest influence on these refugia was during the Wisconsinan glaciation period (c.75 000-10 000 years ago) when the Laurentide ice sheet extended the furthest south (Young et al., 1994;Rempel & Smith, 1998). ...
Two hundred and eighty-seven longnose sucker Catostomus catostomus were collected from 14 lakes in Labrador, 52 from three lakes in Ontario, 43 from two lakes in British Columbia and 32 from a lake in Yukon; a total of 414 in all. The resulting 34 haplotypes (20 in Labrador) contained moderate haplotypic diversity (h = 0·657) and relatively low nucleotide diversity (π = 3·730 × 10(-3) . Mean ϕST (0·453, P < 0·05) over all populations revealed distinct genetic structuring among C. catostomus populations across Canada, based on province, which was validated by the analysis and spatial analysis of molecular variance (c. 80% variation between provinces). These results probably reflect the historical imprint of recolonization from different refugia and possibly indicate limited ongoing gene flow within provinces. A haplotype network revealed one major and two minor clades within Labrador that were assigned to the Atlantic, Beringian and Mississippian refugia, respectively, with tests of neutrality and mismatch distribution indicative of a recent population expansion in Labrador, dated between c. 3500 and 8300 years ago.
... Most freshwater microcrustaceans may disperse equally well via water, animal or aerial connections, Biol (2017) 40:185-198 193 rapidly migrating between discrete localities within a continent or even inter-continentally, despite some limitations due to the priority effect (''monopolization hypothesis''-see De Meester et al. 2002). Nevertheless, the dispersal limitation over broad scales (tens to thousands of kilometres) might constrain their geographic ranges and influence community structure (Weider and Hobaek 1997;Havel and Shurin 2004). This limitation is even more pronounced for the islands and archipelagoes because of the absence of overland pathways for dispersal. ...
Microcrustaceans (MCs) are an important component of freshwater ecosystems, and their local diversity is known to be driven by many factors. What are the relative contributions of these factors at the larger geographic scale? We analyzed the faunal richness and composition of freshwater Cladocera and Copepoda from 27 mainland and insular circumpolar regions (46°–85°N) to determine the main patterns of their species richness and distribution. The average warmest month air temperature was the primary factor affecting MC richness. Regional richness decreased sharply when the temperature dropped below 12–13 °C, and this effect was more pronounced for Cladocera. As a result, the Cladocera/Copepoda species ratio increased significantly with temperature. The total MC richness and cladoceran richness increased with the ice-free area of a region, while the copepod richness decreased on islands with increasing distance from the mainland. Copepod richness was lower in regions that were glaciated during the Quaternary period. Faunal composition significantly differed between cold and warm regions, as well as between the Palearctic and Nearctic, whereas it was affected by neither the glaciation history nor insularity. The contemporary climate had a stronger effect on the cladoceran distribution, whereas the copepods’ ranges were often restricted to a single continent. The former parts of the intercontinental land bridges are primarily inhabited by Holarctic or cosmopolitan species, with almost equal Nearctic and Palearctic components, which indicates repeated colonization events of these regions from various sources. These findings suggest a key role of contemporary climate (especially for cladocerans) and dispersal limitations (primarily for copepods) in structuring MC faunas at high latitudes, and they may help assess possible changes due to global warming.
... The accumulation of genetic data has showed that North American and European D. pulex are genetically two distinct species and nomenclature of the D. pulex complex is not resolved (Colbourne et al., 1998;Palsoon, 2000;Mergeay et al., 2006;Petrusek et al., 2008;Crease et al., 2012;Markova et al., 2013). Even in Europe, asexual strains of D. pulex show a more northerly distribution than sexual ones (Ward et al., 1994;Weider and Hobaek, 1997) and both lineages may co-exist within the same geographical region (Letho and Haag, 2010). In freshwater rock pools on islands of the Baltic sea archipelago (Southern Finland), the asexual strains belong to the North American clade whereas the sexual strains belong to the European clade (Letho and Haag, 2010). ...
This paper reports on the occurrence of Daphnia pulex in a small fishless water body of Northern Italy (Bodrio del pastore III) and describes its population dynamics. Bodrio is a typical water body originated by erosion from the old Po river-bed surface. During a three year study (2011-2013), D. pulex population showed an increase in density from spring to early summer, it declined in July-August and did not recover, presumably from ephippia, until the following spring. The seasonal dynamics was related to the species thermal tolerance and to invertebrate predation by Chaoborus that resulted in juvenile high mortality and in adaptive predator-avoidance cyclomorphosis. Seasonal variation was observed in the frequency of individuals, most juveniles, showing neckteeth. D. pulex population reproduces by cyclical parthenogenesis and showed a very early investment in sexual reproduction, independent of population density. Males and ephippial females appeared at the beginning of growth season before the density peak according to a typical feature of Daphnia populations from temporary habitats. This suggests a lower influence of the environmental factors on sex determination compared to populations inhabiting more permanent habitats. Lineages that produce males and ephippial females early in the season had lower growth rate than parthenogenetic ones but may preserve from selection pressure by predators a significant percentage of genetic variation linked to sex allocation so that evolution proceeds toward earlier and increased sexual reproduction. Our results suggest further investigation to verify whether the current population is the last remnant of a once much larger metapopulation eventually reduced by anthropogenic disturbances or if it represents the invasion of North American strains.
... Palaeoecological evidence indicate that Arctic species survived the Pleistocene glaciations in periglacial areas south of ice sheets in Europe and western Siberia (Kowalski, 1995) and in the non-glaciated area east of the River Lena in eastern Siberia (Sher,199 1). Despite the lack of extant geographic barriers in the Eurasian Arctic, there is evidence for the vicariant events in the dunlin, Calidris a&na (Wenink et al,, 1996), Daphnia pulex (Weider & Hobaek, 1997), and the collared lemming, Dicrostonyx torquatus (Fedorov, Fredga & Jarrell, in press). The significance of historical isolation is strongly supported if the geographical position of phylogenetic division is concordant across different taxa (Avise, 1994). ...
The geographic pattern of mtDNA variation in lemmings from 13 localities throughout the Eurasian Arctic was studied by using eight restriction enzymes and sequencing of the cytochromebregion. These data are used to reveal the vicariant history ofLemmus, and to examine the effect of the last glaciation on mtDNA variation by comparing diversity in formerly glaciated areas to the diversity in non-glaciated areas. Phylogenetic congruence across different Arctic taxa and association between observed discontinuities, and probable Pleistocene barriers, suggest that glacial-interglacial periods were crucial in the vicariant history ofLemmus. Differences in amount of divergence (2.1–9.1%) across different historical barriers indicate chronologically separate vicariant events during the Quaternary. Populations from a formerly glaciated area are no less variable than those in the non-glaciated area. Regardless of glaciation history, no population structure and high haplotype diversity were found within geographic regions. The lack of population structure indicates that populations with high ancestral haplotype diversity shifted their distribution during the Holocene, and that lemmings tracked a changing environment during the Quaternary without reduction of effective population size.
... На фоне общей картины наших знаний о реликтах и рефугиумах, созданной в XX веке, выделяется ряд работ E. Hultén (1937Hultén ( , 1958Hultén ( , 1972, где по сути была сформулирована теория о равнозначных центрах распространения растений, согласно которой виды эволюционируют по мере распространения из рефугиумных центров. Вопреки широко распространенному мнению о полной непригодности местообитаний зон распространения щитового ледника во время плейстоценового ледникового периода для растений, он первым предположил существование рефугиумов даже в самых экстре-мальных условиях и обосновал это с фитогеографических позиций, что позже было подтверждено многочисленными палеофлористическими (Murray, 1981(Murray, , 1995Ritchie, Cwynar, 1982;Colinvaux, West, 1984;Ritchie, 1987Ritchie, , 1992Anderson et al., 1989;Andersen, Bors, 1994;Elias et al., 1996;Edwards et al., 2000;Tarasov et al., 2000;Thompson, Anderson, 2000;Goetcheus, Birks, 2001;Bigelow et al., 2003) и филогеографическими (Abbott et al., 1995(Abbott et al., , 2000Weider, Hobaek, 1997;Tremblay, Schoen, 1999;Alsos et al., 2001;Bronken et al., 2001;Abbott, Brochmann, 2003 и др.) исследованиями. E. Hultén существенно развил понятие «Берингия», предложенное П.П. ...
... Saxifraga oppositifolia, Vaccinium uliginosum and Salix herbacea) are found along with many deposits of D. integrifolia from Beringia and the southeast refugium. Moreover, studies of Arctic animals (the fish Coregonus clupeaformis, collared lemming, caribou, and the fresh water invertebrate genus Daphnia), taken together suggest that up to five refugia existed around the ice during the last glaciation, with general locations corresponding to those proposed here for D. integrifolia (Bernatchez & Dodson 1991; Boileau & Hebert 1991; Eger 1995; Van Raay & Crease 1995; Ferguson 1996; Weider et al. 1996; Weider & Hobaek 1997). But these groups represent only a small fraction of the biota of this region. ...
Abstract Chloroplast DNA variation in the Arctic plant species Dryas integrifolia (Rosaceae) was analysed in relation to both the present-day geographical distribution of populations and to Pleistocene fossil records of this species. The phylogeographical structure was weak but the analysis of haplotype diversity revealed several groups of haplotypes having present-day geographical ranges that overlap locations postulated from geographical and fossil evidence to have been glacial refugia. Based on this information we infer that two important refugial sources of Arctic recolonization by this species were Beringia and the High Arctic. Two other putative refugia, located southeast of the ice sheet and along coastal regions of the eastern Arctic may have served as sources for recolonization of smaller portions of the Arctic. The genetic substructure in the species is mostly due to variation among populations regardless of the ecogeographical region in which they are found. Spatial autocorrelation at the regional scale was also detected. High levels of diversity both within populations and ecogeographical regions are probably indicative of population establishment from several sources possibly combined with recent gene flow.
... Palaeoecological evidence indicate that Arctic species survived the Pleistocene glaciations in periglacial areas south of ice sheets in Europe and western Siberia (Kowalski, 1995) and in the non-glaciated area east of the River Lena in eastern Siberia (Sher, 199 1). Despite the lack of extant geographic barriers in the Eurasian Arctic, there is evidence for the vicariant events in the dunlin, Calidris a&na (Wenink et al,, 1996), Daphnia pulex (Weider & Hobaek, 1997), and the collared lemming, Dicrostonyx torquatus (Fedorov, Fredga & Jarrell, in press). The significance of historical isolation is strongly supported if the geographical position of phylogenetic division is concordant across different taxa (Avise, 1994). ...
The geographic pattern of mtDNA variation in lemmings from 13 localities throughout the Eurasian Arctic was studied by using eight restriction enzymes and sequencing of the cytochrome b region. These data are used to reveal the vicariant history of Lemmus, and to examine the effect of the last glaciation on mtDNA variation by comparing diversity in formerly glaciated areas to the diversity in non‐glaciated areas. Phylogenetic congruence across different Arctic taxa and association between observed discontinuities, and probable Pleistocene barriers, suggest that glacial‐interglacial periods were crucial in the vicariant history of Lemmus. Differences in amount of divergence (2.1–9.1%) across different historical barriers indicate chronologically separate vicariant events during the Quaternary. Populations from a formerly glaciated area are no less variable than those in the non‐glaciated area. Regardless of glaciation history, no population structure and high haplotype diversity were found within geographic regions. The lack of population structure indicates that populations with high ancestral haplotype diversity shifted their distribution during the Holocene, and that lemmings tracked a changing environment during the Quaternary without reduction of effective population size.
... In fact the most interesting feature concerning D. middendorffiana Alpine populations is probably related to their geographical isolation: a remarkable distance exists between arctic and Alpine populations, which suggests fascinating, although speculative, hypothesis on the phylogeny of the Alpine D. middendorffiana. A recent series of studies (Weider & Hobaek 1994;Weider & Hobaek 1997;Colbourne et al. 1998;Hobaek & Weider 1999;Weider et al. 1999a, b;Weider & Hobaek 2003;Paland et al. 2005;Adamowicz et al. 2009) has examined the phylogeography of the artic Daphnia pulex species complex (to which D. middendorffiana belongs) discovering that, in spite of a slow rate of morphological evolution in the Daphniidae, morphologically similar taxa showed high levels of genetic divergence. These studies often involved the arctic populations of D. middendorffiana from North America, Asia and Europe, including the mountain population from the Rockies, but the Alpine population was never analyzed in this global context. ...
Daphnia middendorffiana has an arctic, circumpolar distribution, with some isolated southerly populations restricted to mountainous areas, including the Alps. In this paper, new records of Daphnia middendorffiana on the Alps are reported. The species was regularly recorded in several samples collected from 2006 to 2009 in four high altitude lakes in the Gran Paradiso National Park (GPNP) during the ice free period. This is the third finding for the Alps and the described populations are the largest. Chemical and morphometric features of the lakes are provided, the morphology of the Daphnia middendorffiana from GPNP is described as well as some aspects concerning its ecology. The studied lakes are small, oligotrophic (total phosphorus ranged from 0 to 7 μg L-1) and well preserved from acidification risk (pH ranged from 6.45 to 8.14). D. middendorffiana is the largest zooplanktonic crustacean inhabiting the Alpine lakes in GPNP reaching 3.43 mm in length; the morphological analysis noted some differences within the studied populations; however there is a clear resemblance to the only Alpine population previously described (from Central Alps, Bognanco Valley, Lake Campo IV) and to the arctic populations. D. middendorffiana in GPNP lives at low density levels, reaching higher densities in late August and early September. No males have been found during the sample campaign confirming its ability to produce asexual viable diapauses eggs. This study confirms the attitude of this species for cold and oligotrophic waters and increases the current knowledge on the geographical distribution, morphology and ecology of this species in Alpine environments. The finding of D. middendordorffiana in the GPNP poses interesting issues concerning the phylogeography of Alpine Daphnia middendorffiana, as well as raising need for conservation efforts aimed at keeping the populations safe from several global and local threats, such as climate warming and the ecological impact of alien species.
... The contrast is most striking in N Canada where haplotype diversity is highest along the eastern edge of the Beringian refuge, reaching a maximum on Banks Island. The more recently deglaciated parts of the eastern Canadian Arctic support a much lower diversity of haplotypes, with diversity decreasing significantly with distance from the edge of the Beringian refuge (Weider & Hobaek 1997. These data suggest a longer uninterrupted period of haplotype development within the refuge followed by only limited dispersal into the surrounding geographical areas as the ice sheets retreated. ...
... The accumulation of genetic data has showed that North American and European D. pulex are genetically two distinct species and nomenclature of the D. pulex complex is not resolved (Colbourne et al., 1998;Palsoon, 2000;Mergeay et al., 2006;Petrusek et al., 2008;Crease et al., 2012;Markova et al., 2013). Even in Europe, asexual strains of D. pulex show a more northerly distribution than sexual ones (Ward et al., 1994;Weider and Hobaek, 1997) and both lineages may co-exist within the same geographical region (Letho and Haag, 2010). In freshwater rock pools on islands of the Baltic sea archipelago (Southern Finland), the asexual strains belong to the North American clade whereas the sexual strains belong to the European clade (Letho and Haag, 2010). ...
High rates of survival of Darwinula stevensoni individuals at very low oxygen concentration were observed in a 768 hour laboratory experiment. Organisms from two different habitats (a river and a lake) whose populations were previously shown to be genetically different were used. No difference in hypoxia tolerance was found between individuals from the two habitats. Controls (kept in normoxic conditions and under starvation to match the experimental conditions - food addition would have altered the experiment's oxygen concentrations) had lower survival rates than treated organisms. Within controls, lower rates of survival were found in individuals from the lake than from the river. In a post experiment recovery period (768 hours) we found high survival in treated organisms, an indication of no permanent damage from hypoxia. No difference in survival was found between treated individuals from the lake and the river. Controls that survived starvation in normoxic conditions had lower survival rates than treated organisms. Controls from the lake suffered higher mortality than the ones from the river. Metabolic rate was evaluated by counting the number of respiratory plate beats per minute (Bpm) and the number of eggs produced. Before the beginning of the experiments, river individuals had lower Bpm than lake ones, suggesting a possible correlation with a higher starvation tolerance by riverine populations. Short hypoxia periods induced higher Bpm. A stable minimum was reached after 48 hour exposure to hypoxia. In the later part of the recovery phase Bpm stabilised at a value higher than that observed before the experiment, apparently the only sign of a significant hypoxia effect. Egg production continued, although at a reduced rate, under hypoxia and in the recovery phase.
... pond habitat) within the pulicaria group, while clonal richness is nearly doubled (4.1 clones per population, on average) within the tenebrosa group, a result that might be partially explained by the sporadic presence of sexual reproduction in this group, in certain regions of the arctic (i.e. Beringia, Weider & Hobaek 1997). These levels of clonal richness/diversity are comparable with what is often found in temperate zone populations of obligately parthenogenetic Daphnia ). ...
Current concerns over the impact that anthropogenic global climate change will have on levels of biodiversity have focused mainly on tropical and temperate systems. Recently, attention has turned to polar systems and the potential impacts these climatic changes might have on polar flora and fauna. Polar organisms have been subjected to dramatic fluctuations in environmental conditions during the Holocene and Pleistocene, so one might expect these systems to be resilient. However, little is really known of how such global climate changes will impact biodiversity in the arctic. What is known, particularly through the use of molecular markers, is that glacial cycles have impacted the evolutionary trajectories of many extant polar species. By studying these organisms, particularly those found across the Holarctic, one can examine the dynamic interaction between deterministic forces (e.g. selection) and historical processes (e.g., vicariance event) in order to better understand how these processes have impacted the phylogeography and genetic divergence among taxa. Keeping with the "northern dimensions" theme of this symposium, we review results obtained from a variety of phylogeographic studies that have examined the importance of dispersal, vicariance and selection in shaping the distributions of arctic biota, especially among closely-related species complexes. In particular, We examine the recent debate over the importance of Pleistocene glacial cycles in influencing population genetic differentiation and speciation. Finally, we provide an assessment of how studying these arctic systems will benefit the global perspective on climate change research.
... На фоне общей картины наших знаний о реликтах и рефугиумах, созданной в XX веке, выделяется ряд работ E. Hultén (1937Hultén ( , 1958Hultén ( , 1972, где по сути была сформулирована теория о равнозначных центрах распространения растений, согласно которой виды эволюционируют по мере распространения из рефугиумных центров. Вопреки широко распространенному мнению о полной непригодности местообитаний зон распространения щитового ледника во время плейстоценового ледникового периода для растений, он первым предположил существование рефугиумов даже в самых экстре-мальных условиях и обосновал это с фитогеографических позиций, что позже было подтверждено многочисленными палеофлористическими (Murray, 1981(Murray, , 1995Ritchie, Cwynar, 1982;Colinvaux, West, 1984;Ritchie, 1987Ritchie, , 1992Anderson et al., 1989;Andersen, Bors, 1994;Elias et al., 1996;Edwards et al., 2000;Tarasov et al., 2000;Thompson, Anderson, 2000;Goetcheus, Birks, 2001;Bigelow et al., 2003) и филогеографическими (Abbott et al., 1995(Abbott et al., , 2000Weider, Hobaek, 1997;Tremblay, Schoen, 1999;Alsos et al., 2001;Bronken et al., 2001;Abbott, Brochmann, 2003 и др.) исследованиями. E. Hultén существенно развил понятие «Берингия», предложенное П.П. ...
... Geological ( Hamilton and Thorson 1983;Porter et al. 1983), phytogeographical (e.g. Hopkins 1967), palynological and macrofossil ( Nimis et al. 1998;Edwards et al. 2000;Tarasov et al. 2000;Brubaker et al. 2005;Sher et al. 2005;Birks 2008) and molecular evidence from plants ( Tremblay and Schoen 1999;Abbott et al. 2000;Abbott and Brochmann 2003;Dobes et al. 2004;Abbott and Comes 2004;Alsos et al. 2005;Thompson and Whitten 2006;Brochmann and Brysting 2008), fungi ( Geml et al. 2006), and animals (MacNeil and Strobeck 1987;Bernatchez and Dodson 1991;Quinn 1992;Weider and Hobaek 1997;Reiss et al. 1999;Ehrich et al. 2000;Hundertmark et al. 2001;Federov et al. 2003;Cook et al. 2004;Galbreath and Cook 2004;Waltari et al. 2004) support the Beringia refugium hypothesis. During glacial periods, mountain glaciers and massive ice sheets bounded Beringia, cutting the flora and fauna within the region off from other parts of the tundra (Richmond 1965;Pielou 1991). ...
Background: Evidence strongly suggests that Beringia was a refugium for tundra taxa throughout the Quaternary (the last 2 million years). However, the genetic consequences of the repeated formation and flooding of the Bering Land Bridge remain uncertain.Aims: The goal of this paper was to determine the role that the unique environmental history of Beringia played in the diversification of tundra flora.Methods: I adopted a comparative coalescent approach to test models of divergence for arctic flora within Beringia. The literature was surveyed for phylogeographic studies that sampled broadly across the region and incorporated molecular markers appropriate for coalescent analyses. Of the 13 possible taxa, only two fit these criteria: Saxifraga oppositifolia (Saxifragaceae) and Vaccinium uliginosum (Ericaceae). Observed gene trees were compared with a distribution of trees simulated under neutral coalescence to test models of population divergence. Population models fell within two major categories reflecting the importance of either the Bering Land Bridge or the Bering Sea dispersal barrier on the distribution of genetic diversity in the species.Results: Both species fit ‘bridge’ models, but S. oppositifolia supported a model of eastward migration while V. uliginosum fits a unified Beringia refugium model. The evolutionary implications of these findings are discussed.Conclusions: The limited number of studies emphasises the need for more sequence-based research in the region. This will help resolve the history of the Beringia tundra ecosystem, which has important implications for the diversification of tundra flora, the history of Beringia, and the potential consequences of climate change on the distribution of biological diversity.
... Although the continental ice has not formed geographical barriers to the eastern Palaearctic species, some of these species have genetically differentiated subpopulations. These species include invertebrates (Daphnia pulex, Weider & Hobaek, 1997), small mammals (Lemmus, Fedorov et al., 1999a;Dicrostonyx, Fedorov et al., 1999b) and migratory birds (Calidris alpina, Wenink et al., 1996;Anser erythropus;M. Ruokonen, personal communication). ...
We analysed variation of the mitochondrial control region from willow tits through its Palaearctic distribution range. Although we found high amount of genetic variation (π=1.114%), there was almost no differentiation between subspecies or geographical localities. This may be because of a combination of several ecological and genetic factors, including a relatively homogenic habitat through the distribution range, lack of geographical barriers, high gene flow and a large long-term effective population size. On the contrary, in the songar tit, which is sometimes considered to be conspecific with the willow tit, the mitochondrial lineages seem to correlate with the geographical locality and are clearly distinct from the willow tit. We concluded that the common ancestors of willow and songar tits existed some 1.5–2 Myr ago in the south-eastern Asia. After the last Ice Ages, the willow tit expanded all through the Palaearctic, whereas the songar tit remained in eastern Asia.
... Both the FNV hypothesis and the general-purpose genotype hypothesis assume that clones are able to reach suitable habitats and therefore clonal composition will not be strongly associated with spatial location. Studies that did consider the spatial extent of clones either analysed spatial location independent of environmental properties (Weider & Hebert, 1987; Weider & Hobaek, 1997; Weider et al., 1999) or used Mantel tests that focused on compositional dissimilarity among sites (Aguilera et al., 2007). Legendre et al. (2005) demonstrated that Mantel tests based on compositional dissimilarity could underestimate the amount of variation attributed to environment or space. ...
The rarity of eukaryotic asexual reproduction is frequently attributed to the disadvantage of reduced genetic variation relative to sexual reproduction. However, parthenogenetic lineages that evolved repeatedly from sexual ancestors can generate regional pools of phenotypically diverse clones. Various theories to explain the maintenance of this genetic diversity as a result of environmental and spatial heterogeneity [frozen niche variation (FNV), general-purpose genotype] are conceptually similar to community ecological explanations for the maintenance of regional species diversity. We employed multivariate statistics common in community ecological research to study population genetic structure in the freshwater crustacean, Daphnia pulex × pulicaria. This parthenogenetic hybrid arose repeatedly from sexual ancestors. Daphnia pulex × pulicaria populations harboured substantial genetic variation among populations and the clonal composition at each pond corresponded to nutrient levels and invertebrate predator densities. The interclonal selection process described by the FNV hypothesis likely structured our D. pulex × pulicaria populations.
... A similar latitudinal shift from sexuality in temperate regions to obligate parthenogenesis in the Arctic has been documented in the genus Daphnia (e.g. Weider et al.1987;Weider & Hob×k 1997). ...
Species of Bosmina from the temperate regions of North America and Europe are diploid and reproduce by cyclical parthenogenesis. By contrast, this study provides evidence that the dominant bosminid taxon in High Arctic lakes reproduces by obligate parthenogenesis and is a polyploid derived from interspecific hybridization. Sinobosmina liederi, a species common in temperate North America, is likely to have been one parent of these hybrids, but the other parent is unknown. As neither parent was detected in the Arctic, it seems unlikely that the hybrid clones that now occupy arctic lakes were synthesized locally. Most habitats contained only one or two clones, despite a total of 38 clones in the region, suggesting that priority effects have been important in restricting diversity within single lakes. The high regional diversity of arctic bosminids could reflect either repeated hybridization between the parent taxa or the genetic instability of newly formed polyploid lineages. These processes would produce hybrid polyploids that are considerably more diverse than their sexual parent taxa, and this difference in genetic diversity may confer an advantage to the polyploid biotype. As many zooplankton taxa from the arctic possess genetic characteristics similar to those of bosminids, these processes may provide a general explanation for the widespread occurrence of polyploids in the Arctic.
... Yet, comparatively little is known about daphniid population genetics at nuclear protein-coding loci. Past studies of genetic variation in daphniid populations mainly employed allozymes, microsatellites , and mitochondrial DNA (e.g., Hebert 1974; Mort and Wolf 1986; Crease et al. 1990; Crease et al. 1997; Weider and Hobaek 1997; Palsson 2000), and few population-genetics analyses of nuclear DNA sequences are published (Little et al. 2004; Ishida and Taylor 2007). A better understanding of Daphnia population-genetics parameters will facilitate the interpretation of the new genomic data that are derived from this organism, especially data that are interpreted in an evolutionary context. ...
Understanding nucleotide variation in natural populations has been a subject of great interest for decades. However, many taxonomic groups, especially those with atypical life history attributes remain unstudied, and Drosophila is the only arthropod genus for which DNA polymorphism data are presently abundant. As a result of the recent release of the complete genome sequence and a wide variety of new genomic resources, the Daphnia system is quickly becoming a promising new avenue for expanding our knowledge of nucleotide variation in natural populations. Here, we examine nucleotide variation in six protein-coding loci for Daphnia pulex and its congeners with particular emphasis on D. pulicaria, the closest extant relative of D. pulex. Levels of synonymous intraspecific variation, pi(s), averaged 0.0136 for species in the Daphnia genus, and are slightly lower than most prior estimates in invertebrates. Tests of neutrality indicated that segregating variation conforms to neutral model expectations for the loci that we examined in most species, while K(a)/K(s) ratios revealed strong purifying selection. Using a full maximum-likelihood coalescent-based method, the ratio of the recombination rate to the mutation rate (c/u), averaged 0.5255 for species of the Daphnia genus. Lastly, a divergence population-genetics approach was used to investigate gene flow and divergence between D. pulex and D. pulicaria.
... Previous analyses of mtDNA variation in the Daphnia pulex species complex (Colbourne et al. 1998;Crease et al. 1997;Dufresne and Hebert 1997;Lehman et al. 1995;Van Raay and Crease 1994;Weider and Hobaek 1997;Weider et al. 1996) suggest that many Daphnia ''species'' may have polyphyletic or paraphyletic origins of their mtDNA lineages. Accordingly, few consistent phylogeographic patterns have emerged that would prove useful in the study of gene flow across large physical distances (Crease et al. 1997). ...
Gene flow among invertebrate populations inhabiting bodies of nonflowing freshwater such as ponds or lakes must at some stage involve transport across habitat unsuitable for adult stages. Consequently the potential for interpopulational differentiation is high in these species, yet empirical studies of lake populations of Cladocerans such as Daphnia have failed to reveal high levels of genetic distinctiveness among populations and have led to much speculation about how these populations exchange genes and remain cohesive evolutionary units. In this study we surveyed 42 Oregon lake populations of Daphnia from the D. pulex species complex for genetic variation within the mitochondrial DNA control region. We have used this data to test the relative abilities of various ecological factors to explain the observed patterns in genetic differentiation among lakes. Despite limited genetic variation detected among our samples--11 very similar RFLP-defined mtDNA genotypes from 388 individuals--analyses of nucleotide variance using analogs to Wright's F statistics indicate that when multilake populations are defined in terms of the river drainage basin to which they belong, strong and significant amounts of among-population genetic variation can be detected at this locus (F(ST) estimates between 0.5 and 0.6). In contrast, we fail to detect consistent significant among-population variation when populations are defined on the basis of regional physical geography, bird migratory flyways, or lake trophic status. The manner in which the data are compiled, that is, whether RFLPs or nucleotide sequences are used, has little effect on the overall conclusions, yet it is clear that nucleotide sequence data would lower the standard errors of F(ST) estimates. We propose that periodic widescale flooding during the late Pleistocene may be an important mechanism to homogenize genetic differences among lake Daphnia continent-wide south of the southern-most extent of Pleistocene glaciation.
The lack of morphological variation in many freshwater invertebrates over vast distances has been cited as evidence for their frequent, long-distance dispersal. This scenario implies that vicariance will be an insignificant determinant of species distributions or diversity. We carried out a phylogeographic and population genetics study of one widespread crustacean group, the North American Daphnia laevis complex. Allozyme and sequence variation of two mtDNA genes (12S and 16S rRNA) clearly indicates the existence of five morphologically cryptic, largely allopatric groups (Daphnia dubia, D. laevis laevis, D. laevis gessneri, D. magniceps magniceps, and D. magniceps pacifica ssp. n.). Within each of these groups, there is weak or no genetic differentiation over large geographic areas suggesting their recent long-distance dispersal. The present-day distributions and phylogeography of the regional groups suggests the occurrence of both deep and shallow vicariance events. Although divergence times from mtDNA sequences do indicate both deep and shallow divergences, these estimates are incongruent with their proposed vicariance times. The results show that even within closely related freshwater invertebrates, a complex biogeography exists, whose analysis is made difficult by long-distance dispersal, cryptic endemism, and pseudocongruence.
Pleistocene glacial cycles undoubtedly altered the evolutionary trajectories of many taxa, yet few studies have examined the impact of such events on genetic differentiation and phylogeography at large geographic scales. Here we present the results of a circumarctic survey of mitochondrial DNA diversity in members of the Daphnia pulex complex. The analysis involved the survey of restriction site polymorphisms in a 2100-bp fragment of the NADH-4 (ND4) and NADH-5 (ND5) genes for 276 populations representing the two major groups (tenebrosa and pulicaria) in this complex across their Holarctic range. A comparison of the distribution patterns for seven clades in this complex revealed very clear phylogeographic structuring. Most notably, pulicaria group lineages were restricted primarily to the Nearctic, with some colonization of formerly glaciated portions of northern Europe. This group was not detected from vast expanses of northern Eurasia, including the Beringian glacial refuge. In contrast, tenebrosa group haplotypes showed considerable intercontinental divergence between Eurasian and North American lineages, but were absent from Greenland and Iceland, as well as the Canadian arctic archipelago. Dispersal in Eurasia was primarily in a westerly direction from Beringia, whereas dispersal in the Nearctic followed proglacial drainage patterns. Long-distance dispersal of certain lineages was observed in both groups, and variation in haplotype richness and nucleotide diversity allowed us to make inferences about the positioning of putative glacial refugia. Overall, the phylogeographic pattern of diversification in this arctic complex is characterized by the apparently unique postglacial histories for each clade, indicating that even closely allied taxa can respond independently to the allopatric effects of glacial cycles. This is in sharp contrast to other phylogeographic studies of species assemblages from more southern (unglaciated) latitudes, which are often characterized by concordant patterns.
The continuous generation of genetic variation has been proposed as one of the main factors explaining the maintenance of sexual reproduction in nature. However, populations of asexual individuals may attain high levels of genetic diversity through within-lineage diversification, replicate transitions to asexuality from sexual ancestors and migration. How these mechanisms affect genetic variation in populations of closely related sexual and asexual taxa can therefore provide insights into the role of genetic diversity for the maintenance of sexual reproduction. Here, we evaluate patterns of intra- and inter-population genetic diversity in sexual and asexual populations of Aptinothrips rufus grass thrips. Asexual A. rufus populations are found throughout the world, while sexual populations appear to be confined to few locations in the Mediterranean region. We found that asexual A. rufus populations are characterized by extremely high levels of genetic diversity, both in comparison to their sexual relatives and in comparison to other asexual species. Migration is extensive among asexual populations over large geographic distances, whereas close sexual populations are strongly isolated from each other. The combination of extensive migration with replicate evolution of asexual lineages, and a past demographic expansion in at least one of them, generated high local clone diversities in A. rufus. These high clone diversities in asexual populations may mimic certain benefits conferred by sex via genetic diversity and could help explain the extreme success of asexual A. rufus populations. This article is protected by copyright. All rights reserved.
Many species in North America range northward and barely into southern Canada. Some of these species are classified as species at risk and afforded legal protection in Canada, yet the decision to protect these populations at the edge of their range is controversial. To determine if edge populations are more likely to be listed as at risk, fish species were grouped based on whether they are listed as at risk in Canada then assigned values for several life history and ecological traits and a discriminant function analysis was conducted. Conservation status was correctly predicted 93% of the time. Traits that predicted conservation status were endemic distribution, recognized distinct populations, edge distributions and long-lived.
Northern edge populations of Spotted Gar (Lepisosteus oculatus) were investigated for the presence of local adaptations. Adaptations in the form of delayed age at maturity and lower body condition were seen in the Rondeau Bay population of Spotted Gar. Differences in habitat selection and offshore distance were also seen in the Rondeau Bay population when compared to southern core populations of the species. Microsatellite analyses showed that northern edge populations were divergent from southern core populations and the Rondeau Bay population carried the entirety of the genetic diversity found in the north.
A phylogeny based on mitochondrial gene sequences was created and used to identify five commercially obtained gar samples. Four individuals obtained at a pet shop in Kitchener, Ontario, labeled as Spotted Gar, were identified as Florida Gar (Lepisosteus platyrhincus). A specimen obtained at a commercial fish market in Toronto, Ontario was identified as a Spotted Gar and likely originated from Long Point Bay, Lake Erie.
The presence of local adaptation affirms the need to protect edge populations to conserve the overall diversity within the Spotted Gar and other species in Canada.
The evolutionary history of freshwater zooplankton is still relatively unknown. However, studies of the microcrustaceanDaphniahave revealed interesting patterns; the daphniids that dominate ponds and lakes in the northern hemisphere may have recent origins, likely associated with the glacial advances and retreats during the Pleistocene. Moreover, they form species complexes that actively engage in hybridization and introgression. The present study examines the phylogenetic relationships among circumarctic members of theDaphnia pulexcomplex, through the analysis of sequence diversity in 498 nt of the ND5 mitochondrial gene. Our results suggest that the complex is composed of three major clades, two of which are subdivided into at least eight different lineages. Clearly, species in the complex show genetic discontinuity. Many lineages originated during the Pleistocene, but at least three lineages diverged during the Pliocene. Two taxa (D. pulex, D. pulicaria), thought to be broadly distributed in the northern hemisphere, are shown to be endemic to single continents. In general, the diversification of thepulexcomplex is characterized by rapidly dispersed lineages spanning enormous distances and also by endemism in temperate areas. Gene flow among lineages from the temperate region of different continents are restricted to rare inter-continental migrations across a polar bridge followed by convergent morphological evolution.
The lack of morphological variation in many freshwater invertebrates over vast distances has been cited as evidence for their frequent, long-distance dispersal. This scenario implies that vicariance will be an insignificant determinant of species distributions or diversity. We carried out a phylogeographic and population genetics study of one widespread crustacean group, the North American Daphnia laevis complex. Allozyme and sequence variation of two mtDNA genes (12S and 16S rRNA) clearly indicates the existence of five morphologically cryptic, largely allopatric groups (Daphnia dubia, D. laevis laevis, D. laevis gessneri, D. magniceps magniceps, and D. magniceps pacifica ssp. n.). Within each of these groups, there is weak or no genetic differentiation over large geographic areas suggesting their recent long-distance dispersal. The present-day distributions and phylogeography of the regional groups suggests the occurrence of both deep and shallow vicariance events. Although divergence times from mtDNA sequences do indicate both deep and shallow divergences, these estimates are incongruent with their proposed vicariance times. The results show that even within closely related freshwater invertebrates, a complex biogeography exists, whose analysis is made difficult by long-distance dispersal, cryptic endemism, and pseudocongruence.
This thesis aims at understanding the functioning of high altitude lakes ecosystems in Gran Paradiso National Park. The entire work is based on field data from 20 alpine lakes, collected with a non-manipulative approach.
The organisms inhabiting alpine lakes are subjected to strong environmental pressures, resulting in low diversity and simple food web structure. Although alpine lakes are remote ecosystems, naturally-occurring extreme conditions are superimposed on by several anthropogenic threats interacting with the ecological processes. A main intent of this study is to include these interacting anthropogenic threats in the understanding of ecosystems. The general hypothesis is that the internal ecological dynamic of each lake depends on the interplay of several variables that are unique to each catchment area, such as the pressures exerted by the physical environment, the initial chemical composition of precipitation, the amount and distribution of rain and snowfall, the nature of the surrounding catchment and of the lake basin, and the impact of human activity and land use in the catchment. All these variables determine the sensitivity of each lake toward external influences.
Phylogeographic and taxonomic relationships among 54 North Atlantic populations of the snowbed grass genusPhippsia were investigated based on isozymes and genetically based morphological variation. The results support recognition of two distinct species,P. algida andP. concinna, the latter with at least two subspecies. Both of these self-fertilizing arctic pioneer species were genetic allotetraploids almost without intrapopulational variation. The two species showed strikingly different phylogeographies in the North Atlantic region in spite of their similarity in morphology, habitat ecology, mating system, and dispersal ecology, and in spite of their present cooccurrence in many geographic areas, sometimes even in the same snowbeds. The same electrophoretic multilocus phenotype was observed in all populations ofP. algida, and although this species showed considerable morphological variation, the variation was unstructured geographically. Thus,P. algida showed a pattern similar to other arctic species investigated in the North Atlantic region; it has probably dispersed postglacially across the sea barriers among Greenland, Svalbard, Iceland, and Scandinavia. In contrast,P. concinna was virtually fixed for different multilocus phenotypes in the three main geographic areas analyzed (S Norway, Svalbard, Greenland), corresponding to fairly distinct divergence in morphology. This pattern suggests absence of postglacial among-area dispersal ofP. concinna in spite of all of its similarities with its congener; it may have immigrated to the North Atlantic from different source areas and/or survived the last glaciationin situ.
Previous mitochondrial (mt)DNA sequencing and restriction fragment length polymorphism (RFLP) studies have shown that the Holarctic Daphnia pulex complex is divisible into two major groups (pulicaria and tenebrosa) that exhibit distinct phylogeographic patterns. Here we examine allozymic variation at six polymorphic enzyme loci to ascertain clonal structure and clonal distribution patterns within each group. Specimens were collected from a total of 850 populations encompassing the Arctic. A significant negative relationship (Mantel test) between similarity of regional clonal arrays and geographical distance was observed. A small fraction of clones in each group was widespread (in the order of 1000s of kilometres). However, most clones were restricted to single regions, and were often found only in a single population. These data indicate that the population genetic structure is highly fragmented in this complex, but the potential for long-distance passive dispersal exists. Further, ‘hot spots’ of high clonal richness and diversity were found in each group, which is concordant with earlier work. In addition, ≈ 20% of pulicaria group clones possess nuclear genes from tenebrosa, while approximately 10% of tenebrosa group clones harbour pulicaria nuclear genes. These data indicate nuclear introgression between the two groups, which was found to be prominent in a broad zone of secondary contact encompassing parts of northwestern Russia, northern Fennoscandia, Svalbard, and extending into the high eastern Canadian Arctic.
The growth, survivorship and reproduction of Arctic region Daphnia middendorffiana was investigated in several lakes and ponds on the tundra in northern Alaska and additionally in a laboratory study. Growth rate equations, reproduction rates and survivorship under natural conditions were determined. The natural environments differed in the available resources; investigations were made in undisturbed oligotrophic lakes, lakes undergoing nutrient manipulations, lakes recovering from nutrient manipulation, and a small human-created pond. The lakes also differed in the presence or absence of fish. The results indicated that resource availability affected the growth, survivorship and reproduction of D. middendorffiana. The lake with the highest resources produced the greatest reproduction and growth. The environments with the lowest resources had the least reproduction. Secondly, resource level was observed to influence life history choices. Under low resource conditions D. middendorffiana produced ephippia at first reproduction rather than neonates. Third, the results also indicated that refuge from predation significantly affects the distribution of D. middendorffiana. Lakes that contain fish do not support significant populations of D. middendorffiana, although the growth and survivorship studies indicate they could do well in those environments.
Allozyme variability was studied in 581 Porcellio scaber from 20 population samples in Germany, France, and Poland that were spaced at geographic distances ranging from a few metres to 1200 km. Four of 12 inferred genetic loci proved to be polymorphic (Aat-2*, Gpi*, Mdh-2*, and Pgm*), with three (Aat-2*) to five (Gpi*, Mdh-2*, and Pgm*) alleles each. Average polymorphism (P), observed heterozygosity (Ho), and allelic diversity (AD) were 0.329, 0.155, and 1.72, respectively. Genetic among-sample distances, fixation indices, and principle component analysis of allele frequencies indicate considerable genetic homogeneity throughout the study area, except for one of two population samples from offshore islands. Isolation by distance was indicated by increasing genetic distances and declining fixation indices with increasing geographical distance between collection sites. The population genetic homogeneity of a litter-dwelling organism lacking efficient means for active dispersal is interpreted as resulting from the recent postglacial recolonization of the study area from a single ice age refugial area, by the large effective population size of P. scaber, and by passive human-aided dispersal.
The distribution pattern of mtDNA haplotypes in distinct populations of the glacial relict crustacean Saduria entomon was examined to assess phylogeographic relationships among them. Populations from the Baltic, the White Sea and the Barents Sea were screened for mtDNA variation using PCR-based RFLP analysis of a 1150 bp fragment containing part of the CO I and CO II genes. Five mtDNA haplotypes were recorded. An analysis of geographical heterogeneity in haplotype frequency distributions revealed significant differences among populations. The isolated populations of S. entomon have diverged since the retreat of the last glaciation. The geographical pattern of variation is most likely the result of stochastic (founder effect, genetic drift) mechanisms and suggests that the haplotype differentiation observed is probably older than the isolation of the Baltic and Arctic seas.
The evolutionary history of freshwater zooplankton is still relatively unknown. However, studies of the microcrustacean Daphnia have revealed interesting patterns; the daphniids that dominate ponds and lakes in the northern hemisphere may have recent origins, likely associated with the glacial advances and retreats during the Pleistocene. Moreover, they form species complexes that actively engage in hybridization and introgression. The present study examines the phylogenetic relationships among circumarctic members of the Daphnia pulex complex, through the analysis of sequence diversity in 498 nt of the ND5 mitochondrial gene. Our results suggest that the complex is composed of three major clades, two of which are subdivided into at least eight different lineages. Clearly, species in the complex show genetic discontinuity. Many lineages originated during the Pleistocene, but at least three lineages diverged during the Pliocene. Two taxa (D. pulex, D. pulicaria), thought to be broadly distributed in the northern hemisphere, are shown to be endemic to single continents. In general, the diversification of the pulex complex is characterized by rapidly dispersed lineages spanning enormous distances and also by endemism in temperate areas. Gene flow among lineages from the temperate region of different continents are restricted to rare intercontinental migrations across a polar bridge followed by convergent morphological evolution.
The development of cost-effective molecular tools allowing the amplification of minute amounts of DNA effectively opened the field of molecular ecology for rotifers. Here I review these techniques and the advances they have provided in the understanding of sibling species complexes, clonal structure, resting egg banks, population structure, phylogeographic patterns and phylogenetic relationships in rotifers. Most of the research to date has focused on the rotifer species complex Brachionus plicatilis. The use of DNA sequence and microsatellite variation, in the context of the background knowledge of life history, mating behaviour, and temporal population dynamics in these organisms have revolutionised our views into the processes shaping the genetic diversity in aquatic invertebrates. Rotifers have populations with a very high number of clones in genetic equilibrium. In temporary populations clonal selection is effective in eroding the number of clones. Rotifer populations are strongly differentiated genetically for neutral markers, even at small geographical scales, and exhibit deep phylogeographic structure which might reflect the impact of Pleistocene glaciations. Despite the high potential for dispersal afforded by resting eggs, rotifers display persistent historical colonisation effects, with gene flow effective only at a local scale and with marked isolation by distance. Instances of long-distance transcontinental migration resulting in successful colonisation have also been revealed. B. plicatilis is composed of a group of several ancient species and sympatry is common. Despite this, the presence of cosmopolitan species in this species complex cannot be discounted. I discuss future priorities and point out the main areas where our knowledge is still insufficient.
Asexual reproduction is commonly thought to be associated with low genetic diversity in animals. Echmepteryx hageni (Insecta: 'Psocoptera') is one of several psocopteran species that are primarily parthenogenetic, but also exists in small, isolated sexual populations. We used mitochondrial DNA sequences to investigate the population history and genealogical relationships between the sexual and asexual forms of this species. The asexual population of E. hageni exhibits extremely high mitochondrial haplotype diversity (H=0.98), whereas the sexual forms had significantly lower haplotypic diversity (H=0.25, after correcting for sample size). This diversity in asexuals represents one the greatest genetic diversities reported for asexual animals in the literature. Nucleotide diversities were also higher in asexual compared to sexual populations (π=0.0071 vs. 0.00027). Compared to other reported estimates of π in insects, asexual nucleotide diversity is high, but not remarkably elevated. Three hypotheses might explain the elevated genetic diversity of asexual populations: (i) larger effective population size, (ii) greater mutation rate or (iii) possible recent origin of sexuals. In addition, phylogeographic analysis revealed little geographic structure among asexual E. hageni, although specimens from the upper Midwest form a single clade and are genetically differentiated. The mismatch distribution and neutrality tests indicate a historical population size increase, possibly associated with expansion from glacial refugia.
North-western North America has been repeatedly glaciated over most of the past two million years, with the most recent glaciation occurring between 60 000 and 10 000 years ago. Intraspecific genetic variation in many species has been shaped by where they survived glaciation and what postglacial recolonization routes were used. In this study, molecular techniques were used to investigate biogeographical, taxonomic and conservation issues in rainbow trout, Oncorhynchus mykiss. Mitochondrial DNA (mtDNA) variation was assessed using a restriction fragment length polymorphism (RFLP) analysis, focusing mainly on the previously understudied northern extent of the species' range. Two phylogenetically distinct mitochondrial lineages were found that differed from each other by up to 1.8% in sequence. Although the geographical distributions of the two clades overlap extensively, diversity and distributional analyses strongly suggest that trout survived glaciation in both coastal and inland refugia followed by postglacial gene flow and secondary contact. Postglacial dispersal into British Columbia most likely occurred from the Queen Charlotte Islands and the Columbia River. Although trout most likely also survived glaciation along the coast of Washington, Oregon and California, as well as near the Bering Strait, evidence suggests that dispersal into British Columbia from these areas was limited. Sequence analysis of mitochondrial haplotypes revealed higher diversity in California than in the northern part of the species' range, indicating an ancient presence of the species in the south. Phylogeographic divergence probably predates adaptive variation in the species as suggested by evidence for parallel evolution of life history types across the range of O. mykiss.
We studied the structure of genetic variation (at both ramet- and genet-level) and clonal diversity within and among populations in the four closely related arctic clonal sedges Carex bigelowii, C. ensifolia, C. lugens and C. stans by use of allozyme markers. Compared to other sedges and arctic plants, the studied taxa all had high levels of genetic variation, both within populations and taxa. These taxa contained most of the total gene diversity (H(T)) within populations and a small part of the diversity among populations (G(ST) ranged 0.05--0.43). Carex bigelowii had genetic variation (H(S) = 0.173, mean for populations) at a comparable level to other outbreeding arctic plants and to other widespread, rhizomatous and mainly outbreeding Carex species. In contrast, C. ensifolia (H(S) = 0.335), C. lugens (H(S) = 0.339) and C. stans (H(S) = 0.294) had within-population variations that were higher than in most other studied Carex species and for arctic plants in general. Genetic variation was not related to any tested environmental variable, but it was lower in areas deglaciated only 10,000 years BP compared to areas deglaciated 60,000 years BP or not glaciated at all during the Weichselian. All the populations were multiclonal, except for two populations of C. stans that were monoclonal. In contrast to genetic variation, clonal diversity decreased with latitude and did not differ between areas with different times of deglaciation. In accordance with previous studies, C. bigelowii and C. lugens were found to be outbreeding, while C. ensifolia and C. stans had mixed mating systems.
Phylogeographic analyses have revealed the importance of Pleistocene vicariance events in shaping the distribution of genetic diversity in freshwater fishes. However, few studies have examined the patterning of variation in freshwater organisms with differing dispersal syndromes and life histories. The present investigation addresses this gap, examining the phylogeography of Sida crystallina, a species whose production of diapausing eggs capable of passive dispersal was thought to constrain its regional genetic differentiation. By contrast, the present analysis has revealed deep allozyme and cytochrome oxidase I mitochondrial DNA divergence between populations from North America and Europe. Moreover, North American populations are separated into four allopatric assemblages, whose distribution suggests their derivation from different Pleistocene refugia. These lineages show higher haplotype diversity and deeper sequence divergence than those of any fish from temperate North America. Its distinctive life history traits have evidently sheltered lineages of Sida from extinction, contributing to a remarkably comprehensive and high resolution phylogeographic record.
Ploidy-level variation among asexual clones of Daphnia pulex showed a clear latitudinal pattern. Only a single diploid clone was identified at the high-arctic Igloolik site, and it comprised only 2% of the individuals in the populations at that locality (clone 43 in Weider et al. 1987). Conversely, at Windsor, the temperate site, only diploids were found; and at the low-arctic locality of Churchill, both diploids and polyploids were common. The clear association between latitude and ploidy level supports the view that polyploidy is selected for in extreme environments. If representative of a general trend in animals, these results suggest that geographical patterns in the distribution of parthenogens arise from indirect rather than direct selection for shifts in the breeding system.
The rarity of polyploidy in animals is often linked to the direct or indirect effects of sex determination mechanisms, a view reinforced by the general association between transitions to unisexuality and polyploidy. However, polyploids are surprisingly uncommon in groups that either engage in bouts of unisexual reproduction or lack sex chromosomes. This study uses a polymerase chain reaction (PCR) amplified region of the ND4-ND5 genes of the mitochondrial genome and allozyme markers to investigate the origins of polyploidy in one group which combines both these attributes: cladoceran crustaceans belonging to the Daphnia pulex (Leydig) complex. Our results show that all of the polyploid clones in this complex originated through interspecific hybridization. A group of melanic polyploid clones were formed through hybridization of three distinct clusters of D. pulicaria or D. melanea with D. pulex, whereas unpigmented polyploid clones originated following hybridization between D. pulex and a more genetically divergent species, D. middendorffiana. This hybridization event was followed by either the ejection or silencing of the maternal nuclear genome, which resulted in the near complete homozygosity of these clones. Our results suggest that the low frequency of hybridization events in animals may be a primary factor constraining the origin of polyploidy in this kingdom.
Concerns genetic variability in the nominate subspecies, O. d. dalli, from 3 parts of its N Alaskan distribution: the Alaskan Range, the Tanana Hills and the Brooks Range. These areas are 150-200 km apart. Their populations have been isolated from each other since the end of the Wisconsinan glaciation. -from Authors
Genome size determinations were coupled with allozyme and mtDNA studies to gain insights into the origin of polyploidy and clonal diversity in populations of Daphnia tenebrosa from Churchill, Manitoba. Allozymic variation at five enzyme loci allowed the detection of 32 clones. Analyses of 73 populations in 1981, 27 in 1987 and 45 in 1991 revealed that clonal frequencies were relatively stable and that D. tenebrosa was more clonally diverse (average of three clones per pond) than other species of the D. pulex complex at the same site. Genome size determinations revealed the presence of two clonal assemblages with averages of 0.53 (± 0.01) pg and 0.89 (± 0.03) pg, corresponding to diploid and tetraploid clones. Clustering of allozyme distances revealed three groups, with no association between ploidy level or pigmentation. Similarly, diploid and polyploid clones did not form distinct clusters on the mtDNA dendrogram. The high sequence divergence between the two mtDNA clusters as well as the lack of correspondence between allozyme distance and mtDNA divergence among clonal pairs both suggest that polyploidy arose following reciprocal hybridizations between genetically divergent populations of this species.
Two statistics are proposed for summarizing spatial patterns of DNA diversity. These autocorrelation indices for DNA analysis, or AIDAs, can be applied to RFLP and sequence data; the resulting set of autocorrelation coefficients, or correlogram, measures whether, and to what extent, individual DNA sequences or haplotypes resemble the haplotypes sampled at arbitrarily chosen spatial distances. Analyses of computer-generated sets of data, and of RFLP data from two natural populations, show that AIDAs allow one to objectively and simply identify basic patterns in the spatial distribution of haplotypes. These statistics, therefore, seem to be a useful tool both to explore the genetic structure of a population and to suggest hypotheses on the evolutionary processes that shaped the observed patterns.
Based largely on analogy with latitudinal trends in species diversity, it has been proposed that levels of genotypic (clonal) diversity in parthenogenetic populations from high latitudes should be lower than those in populations from the temperate zone or the tropics. Prior studies have shown that low-arctic populations of obligately asexual Daphnia pulex are less clonally diverse than temperate-zone populations. To test for the existence of a latitudinal trend, an allozymic survey of obligately parthenogenetic populations of D. pulex was conducted at a site in the Canadian high-arctic. The study revealed the presence of 75 clones in 179 tundra ponds that were surveyed. On average, 4.5 clones coexisted in single ponds with a range of 1-14 clones. These diversity values are as great (or greater) than those observed in more southerly populations and conflict with the notion of reduced levels of genetic variation in arctic populations. Mechanisms that may influence genetic (clonal) diversity in apomictic complexes are discussed.
Preface. Part I: Background: 1. Introduction. Why Employ Molecular Genetic Markers? Why Not Employ Molecular Genetic Markers? 2. History of Molecular Phylogenetics. Debates and Diversions from Molecular Systematics. Molecular Phylogenetics. 3. Molecular Tools. Protein Assays. DNA Assays. References to Laboratory Protocols. 4. Interpretative Tools. Categorical Subdivisions of Molecular Genetic Data. Molecular Clocks. Procedures for Phylogeny Reconstruction. Gene Trees versus Species Trees. Part II: Applications: 5. Individuality and Parentage. Genetic Identity versus Non-Identity. Parentage. 6. Kinship and Intraspecific Phylogeny. Close Kinship and Family Structure. Geographic Population Structure and Gene Flow. Phylogeography. Microtemporal Phylogeny. 7. Speciation and Hybridization. The Speciation Process. Hybridization and Introgression. 8. Species Phylogenies and Macroevolution. Rationales for Phylogeny Estimation. Special Approaches to Phylogeny Estimation. Prospectus for a Global Phylogeny. Special Topics in Molecular Phylogenetics. 9. Conservation Genetics. Issues of Heterozygosity. Issues of Phylogeny. Literature Cited. Index to Taxonomic Genera. General Index.
Some individuals of the cladoceran crustacean, Daphnia pulex, reproduce by cyclic parthenogenesis, while others are obligate parthenogens. Cyclic parthenogenesis is the primitive breeding system; the transition to obligate parthenogenesis has been linked to sex-limited meiosis-suppression. Detailed study of patterns of breeding-system distribution and clonal diversity is justified because D. pulex is the first species in which the loss of sex has been related to this mechanism. The present study investigated the genotypic characteristics of 10 D. pulex populations from each of 22 sites in the Great Lakes watershed. This analysis revealed that populations reproducing by cyclic parthenogenesis were uncommon and restricted to southern sites. Most populations reproduced by obligate parthenogenesis, with the electrophoretic survey revealing an average of three clones per pond and 145 unique clones over the watershed. A combinatorial analysis was used to examine the relationships between clone discovery in the asexual populations and both sample size and genetic-sampling intensity. This analysis showed that the few clones found in individual ponds were readily discriminated, while diversity on a regional scale was underestimated. These methods provide a quantitative basis for assessing the level of clonal diversity in asexual populations and in asexually transmitted segments of the genome.
Most parthenogenetic animal taxa which have been investigated electrophoretically, cytologically, or with tissue grafting techniques are clonally diverse. I have examined data on multiclonal parthenogenetic populations using ecological diversity measures to elucidate patterns of clonal coexistence. Analysis of a discrete population cage experiment on clones of Drosophila mercatorum revealed monotonic decay of clonal diversity and evenness; however, in a continuous generation cage, clonal diversity appeared to stabilize. Clonal diversity and evenness fluctuated widely over time in several multiclonal populations of Daphnia magna although no clonal extinction was observed. There were few spatial trends in clonal diversity and evenness within parthenogenetic taxa. It is suggested that the degree of clonal differentiation, determined by the mode of clonal origin, is important in determining whether or not selection occurs among sympatric clones
A survey of allozyme diversity within and between populations of Silene acaulis from Spitsbergen, Norway, Iceland and Scotland, showed that populations from the high Arctic (Spitsbergen, > 76°N) contained high levels of diversity and were genetically similar to populations from more southern locations. Indirect measures of gene flow (Nm), calculated from Wrigh's F indicated that there had been extensive gene flow between Spitsbergen and some Norwegian populations. A restriction site analysis of chloroplast DNA (cpDNA) in S. acaulis revealed that all populations contained a single identical cpDNA haplotype, except one population from Norway which also contained a second haplotype. In contrast, five different cpDNA haplotypes were distinguished in a more limited survey of cpDNA variation in Saxifraga oppositifolia, with all five haplotypes present in one of two Spitsbergen populations surveyed. The contrasting cpDNA results for the two species suggest that whereas high-Arctic populations of Silene acaulis have most likely been derived from immigrants which arrived from the south after the last glacial period, high-Arctic populations of Saxifraga oppositifolia may be derived, in part, from ancient northern stocks which survived the last glaciation in high-Arctic refugia.
A survey was made of the occurrence of zooplankton in fresh and brackish waters at Cape Thompson, Alaska between June 28, 1960 and August 7, 1961.Fourteen species of Cladocera and 38 species of Copepoda (13 Calanoida, 11 Cyclopoida and 14 Harpacticoida) were distinguished in collections from 10 lakes, 8 lagoons, and 111 pools.Males of Daphnia middendorffiana are illustrated and their geographical significance discussed.
Cyclops scutifer had the only hibernal developmental cycle; all others had developmental cycles during early summer or throughout the summer and fall.Relatively complete seasonal developmental cycles are presented for Holopedium gibberum, Daphnia middendorf iana, Heterocope septentrionalis, Eurytemora canadensis, E. gracilicauda, Limnocalanus johanseni, Diaptomus pribilofensis, D. arcticus, Cyclops scutifer, and C. magnus.Eine bersicht des Vorkommens vom Zooplankton in der Zeit zwischen dem 28. juni, 1960 and dem 7. August 1961 im Ssswasser und im Brackwasser des Kaps Thompson, Alaska wird hier gegeben.Von den Sammlungen aus 10 Seen, 8 Lagunen and 111 Teichen sind 14 Spezies der Cladoceren and 38 Spezies der Copepoden (darunter 13 der Calanoiden, 11 der Cyclopoiden, und 14 der Harpacticoiden) unterschieden worden.Die mnnlichen der Daphnia middendorfliana werden hierin illustriert und die geographische Bedeutung erlutert.
Cyclops scutifer hatte den einzigen winterlichen Entwicklungszyklus; die anderen hatten Entwicklungszyklen frh in dem Frhling oder whrend des ganzen Sommers and Herbstes.Jahreszeitliche Entwicklungszyklen, die verhltnismssig vollkommen sind, werden fr die folgenden vorgefhrt: Holopedium gibberum, Daphnia middendorffiana, Heterocope septentrionalis, Eurytemora canadensis, E. gracilicauda, Limnocalanus johanseni, Diaptomus pribilofensis, D. arcticus, Cyclops scutifer, und C. magnus.
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Incluye bibliografía e ìndice
Thesis (Ph. D.)--University of Kansas, Zoology, 1964. Includes bibliographical references.
THE cause of extinction of the woolly mammoth, Mammuthus primigenius (Blumenbach), is still debated. A major environmental change at the Pleistocene-Holocene boundary, hunting by early man, or both together are among the main explanations that have been suggested. But hardly anyone has doubted that mammoths had become extinct everywhere by around 9,500 years before present (BP). We report here new discoveries on Wrangel Island in the Arctic Ocean that force this view to be revised. Along with normal-sized mammoth fossils dating to the end of the Pleistocene, numerous teeth of dwarf mammoth dated 7,000-4,000 yr BP have been found there. The island is thought to have become separated from the mainland by 12,000 yr BP. Survival of a mammoth population may be explained by local topography and climatic features, which permitted relictual preservation of communities of steppe plants. We interpret the dwarfing of the Wrangel mammoths as a result of the insularity effect, combined with a response to the general trend towards unfavourable environment in the Holocene.
A simple method of the maximum likelihood estimation of the number of nucleotide substitutions is presented for the case where restriction sites data from many different restriction enzymes are available. An iteration method, based on nucleotide counting, is also developed. This method is simpler than the maximum likelihood method but gives the same estimate. A formula for computing the variance of a maximum likelihood estimate is also presented.
Cyclic parthenogenesis is the ancestral mode of reproduction in the cladoceran crustacean, Daphnia pulex, but some populations have made the transition to obligate parthenogenesis and this is the only mode of reproduction known to occur in arctic populations. Melanism and polyploidy are also common in arctic populations of this species. Prior allozyme studies of arctic D. pulex revealed substantial levels of clonal diversity on a regional scale. Clonal groupings based on cluster analysis of allozyme genotypes do not conform to groupings based on the presence/absence of melanin or on ploidy level. In order to further elucidate genetic relationships among arctic D. pulex clones, mitochondrial DNA (mtDNA) variation was examined in 31 populations from two Canadian high-arctic sites. The data were also compared to a previous study of mtDNA variation in populations from a Canadian low-arctic site. Cladistic analysis of restriction site variation of the entire mitochondrial genome and nucleotide sequence variation of the mitochondrial control region was used to construct genetic relationships among mitochondrial genotypes. Three distinct mitochondrial lineages were detected. One lineage was associated with diploid, nonmelanic clones and is the same as the lineage that is found in temperate populations of D. pulex. The other two lineages (A & B) were associated with polyploid, melanic clones. Sequence divergence between the A and B lineages was 2.4%. Sequence divergence between D. pulex and either of these two lineages exceeded 3%.(ABSTRACT TRUNCATED AT 250 WORDS)
An electrophoretic survey of 81 populations of arctic Daphnia pulex from around the Svalbard archipelago revealed the presence of 49 unique allozyme clones (N = 3357). Two closely related clones accounted for 66% of the total sample, and were widespread across the archipelago. Restriction fragment length polymorphisms (RFLPs) of a 2.1-kb fragment of mtDNA (NADH-4 and NADH-5 subunits), amplified using the polymerase chain reaction (PCR), revealed the presence of eight mtDNA haplotypes. One haplotype was particularly widespread, and the two most abundant allozyme clones shared this haplotype. Nonrandom distribution patterns of clones were observed, and are most likely the result of historical events (i.e. founder effects) related to the past glacial history of the archipelago. The data are discussed with reference to past glaciation events, and attempts are made to discern the colonization history of this apomictic complex.
As part of a continuing international project to characterize the population genetic (clonal) structure of arctic members of the Daphnia pulex complex, 34 populations from western Iceland (N = 1373), and 76 populations from western Greenland (N = 2917), were surveyed for allozymic variation at six polymorphic enzyme loci. Mean clonal richness (+/- SE) was 1.91 +/- 0.19 and 1.50 +/- 0.12 for Iceland and Greenland populations, respectively. Mean clonal diversity (+/-1 SE) was 1.20 +/- 0.07 and 1.13 +/- 0.04 for Iceland and Greenland populations, respectively. Four widely distributed clones constituted 92.2% of the total animals surveyed from Iceland, while three locally abundant clones constituted 80.1% of the total animals collected primarily from Disko Island, western Greenland. Selected populations were screened for mitochondrial (mt)DNA variation using PCR-based RFLP analysis of a 2100 bp fragment containing part of the ND4 and ND5 genes. One mtDNA haplotype was very widespread in both western Greenland and western Iceland, although, a number of mutational derivatives were also detected. These data indicate the potential for long-distance dispersal of mtDNA lineages, of the order of hundreds or thousands of kilometers across the arctic. Phylogenetic analysis of the sequence of a 254 base pair (bp) fragment of the control region of the mtDNA molecule revealed two major clades one of which consisted solely of non-melanic lineages, and the other of which consisted almost exclusively of melanic lineages (i.e. one non-melanic lineage also clustered in this clade). Sequence divergence between the two clades averaged 7.3%. Both mitochondrial analyses did not reveal any distinct intraregional clustering of lineages. We discuss our results in reference to previous molecular work done on this arctic Daphnia complex, and we attempt to infer phylogeographic patterning based on geological/glaciological historical events in this region of the arctic.
Mitochondrial DNA diversity in an apomictic Daphnia complex from the Canadian high arctic Holocene dwarf mammoths from Wrangel Island in the Siberian arctic Molecular biogeog-raphy of clonal lineages in a high-arctic apomictic Daphnia complex
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REAP - The Restriction Enzyme Analysis Package
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