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![Precursor island regions, lineages, transects, and ecotone on Martinique.
Geological boundaries between precursor islands are indicated by red lines. They are occupied by lineages labelled in red (NW = northwest, C = central, SW = southwest, S = south). The ecotone between xeric coastal and montane rainforest is indicated by a green, broken line, and the section of Transect III devastated by the 1902 pyroclastic surges that destroyed St Pierre [31] is indicated by grey shading. Transects and their sites are in blue and numbered with blue Roman numerals I to IX. The control transect (IX) within the central mesic zone, is without an ecotone or secondary contact. The photographs are of adult male anoles (locality on Martinique indicated by boxed numbers), 1 northeastern coastal, 2 littoral coastal form, 3 montane rainforest form, 4 widespread mesic/transitional form, and 5 xeric form occurring in the western rainshadow, St Anne Peninsular in the south and the eastern tip of the Caravelle peninsular in east where annual rainfall is circa 1500mm a year or less [50].](profile/Roger-Thorpe-2/publication/44573535/figure/fig4/AS:341317059137565@1458387736894/Precursor-island-regions-lineages-transects-and-ecotone-on-Martinique-Geological.png)
Precursor island regions, lineages, transects, and ecotone on Martinique. Geological boundaries between precursor islands are indicated by red lines. They are occupied by lineages labelled in red (NW = northwest, C = central, SW = southwest, S = south). The ecotone between xeric coastal and montane rainforest is indicated by a green, broken line, and the section of Transect III devastated by the 1902 pyroclastic surges that destroyed St Pierre [31] is indicated by grey shading. Transects and their sites are in blue and numbered with blue Roman numerals I to IX. The control transect (IX) within the central mesic zone, is without an ecotone or secondary contact. The photographs are of adult male anoles (locality on Martinique indicated by boxed numbers), 1 northeastern coastal, 2 littoral coastal form, 3 montane rainforest form, 4 widespread mesic/transitional form, and 5 xeric form occurring in the western rainshadow, St Anne Peninsular in the south and the eastern tip of the Caravelle peninsular in east where annual rainfall is circa 1500mm a year or less [50].
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From Darwin's study of the Galapagos and Wallace's study of Indonesia, islands have played an important role in evolutionary investigations, and radiations within archipelagos are readily interpreted as supporting the conventional view of allopatric speciation. Even during the ongoing paradigm shift towards other modes of speciation, island radiati...
Citations
... If segregation of specific terrain or higher life forms living there led to the formation of distinctive symbiotic microbial species in a similar kind of specific environment, it can also be an effective method to obtain maximized new microbial species. Geographical isolation might trigger the appearance and continued emergence of new ecotypes of micro-organisms over time [14][15][16]. A quantitative investigation is, thus, required to evaluate this hypothesis. ...
This study hypothesized that geographic segregation of certain extreme natures of the same kind could be an indicator of access to new natural microbial resources. Root-layer fungi and soil properties native to well-conserved volcanic topographies from two geographically segregated ocean volcanic islands beside the Korean Peninsula were analyzed. Four segregated sampling sites that represented the ocean volcanoes’ unique natural characters (tuff layer, caldera, and two steep cliffs) were examined. A total of 1356 operational taxonomic units classified into 7 phyla and 196 genera were obtained. Soil analysis showed that the sand proportion varied from 32.0–57.4%, and silt, 39.4–64.8%. The tuff layer terrain was the only terrain classified as silt soil. Soil Corg contents ranged from 2.78–15.12%; TN, 0.159–0.843; salinity, 0.001–0.019; and pH, 5.0–7.4. The larger the island area, the less oceanic salinity inflow, but TN and Corg decreased, and pH increased. The Shannon diversity index varied from 4.81–5.23 and was higher at the larger or center of larger islands. As geographic segregation (distance) increased, the proportion of taxa commonly identified decreased. Thus, geographic isolation of certain natural features (e.g., volcanic islands) may be a preferential clue to accessing a broader range of potential microbial resources.
... This was accomplished using resistance surfaces parameterized as the inverse of predicted habitat suitability (MacDonald et al., 2020;McRae & Beier, 2007;Storfer et al., 2010;Wang et al., 2008Wang et al., , 2012. This approach assumes that organisms are more likely to disperse within suitable habitat and experience high resistance when moving through unsuitable habitat (Crispo et al., 2006;MacDonald et al., 2020;McRae, 2006;McRae & Beier, 2007;Sánchez-Ramírez et al., 2018;Thorpe et al., 2008Thorpe et al., , 2010. Although configurations of suitable habitat may not influence gene flow within butterfly species at fine spatial scales due to considerable adult vagility (e.g., MacDonald et al., 2020), large stretches of unsuitable habitat are likely to pose significant barriers to gene flow among parapatric and allopatric species at larger spatial scales (Coyne & Orr, 2004;Nosil, 2012). ...
Recent advances in both genomics and ecological modelling present new, multidisciplinary opportunities for resolving species boundaries and understanding the mechanisms that maintain their integrity in regions of contact. Here, we use a combination of high‐throughput DNA sequencing and ecological niche modelling to resolve species boundaries and niche divergence within the Speyeria atlantis‐hesperis (Lepidoptera: Nymphalidae) complex, a confusing group of North American butterflies. This complex is notorious for its muddled species delimitations, morphological ambiguity, and extensive mito‐nuclear discordance. Our admixture and multispecies coalescent‐based analyses of single nucleotide polymorphisms identified substantial divergences between S. atlantis and S. hesperis in areas of contact, as well as between distinct northern and southern lineages within S. hesperis. Our results also provide evidence of past introgression relating to another species, S. zerene, which previous work has shown to be more distantly related to the S. atlantis‐hesperis complex. We then used ecological models to predict habitat suitability for each of the three recovered genomic lineages in the S. atlantis‐hesperis complex and assess their pairwise niche divergence. These analyses resolved that these three lineages are significantly diverged in their respective niches and are not separated by discontinuities in suitable habitat that might present barriers to gene flow. We therefore infer that ecologically‐mediated selection resulting in disparate habitat associations is a principal mechanism reinforcing their genomic integrity. Overall, our results unambiguously support significant evolutionary and ecological divergence between the northern and southern lineages of S. hesperis, sufficient to recognize the southern evolutionary lineage as a distinct species, called S. nausicaa based on taxonomic priority.
... The geomorphic traits of the Korean peninsula are derived from old landforms and young volcanic islands (Figure 1(A)). Such diverse natural topography induces geographical segregations, leading to ecological isolation of higher organisms and lack of genetic exchange [15][16][17][18]. To assess how geographical isolation affects the characteristics and uniqueness of fungal microflora, three sites in two volcanic islands located offshore from the mainland Korean peninsula, including the Dongdo Islands (a constituent of Dokdo Islands) (Figure 1(B)), Sadong ( Figure 1(C1)), and Taeha ( Figure 1(C2)) in the Ulleungdo Islands (Figure 1(C)), were selected. ...
This study aimed to understand whether the geo-ecological segregation of native plant species affects the root-associated fungal community. Rhizoplane (RP) and rhizosphere (RS) fungal microbiota of Sedum takesimense native to three geographically segregated coastal regions (volcanic ocean islands) were analyzed using culture-independent methods: 568,507 quality sequences, 1399 operational taxonomic units, five phyla, and 181 genera were obtained. Across all regions, significant differences in the phyla distribution and ratio were confirmed. The Chao’s richness value was greater for RS than for RP, and this variance coincided with the number of genera. In contrast, the dominance of specific genera in the RS (Simpson value) was lower than the RP at all sites. The taxonomic identity of most fungal species (95%) closely interacting with the common host plant was different. Meanwhile, a considerable number of RP only residing fungal genera were thought to have close interdependency on their host halophyte. Among these, Metarhizium was the sole genus common to all sites. These suggest that the relationship between potential symbiotic fungi and their host halophyte species evolved with a regional dependency, in the same halophyte species, and of the same natural habitat (volcanic islands); further, the fungal community differenced in distinct geographical regions. Importantly, geographical segregation should be accounted for in national culture collections, based on taxonomical uniqueness.
... Furthermore, pharmacologically active compounds such as chlorogenic acid have also been identified in C. takesimana. It is presumed that its unique antioxidant traits have resulted from a gradual adaptation to the harsh marine environment of these oceanic islands since mycorrhizal symbiosis may alter phenolic acid content in plants and the host plants may establish an efficient way to increase stress tolerance under certain conditions through this mechanism [12][13][14]. ...
... It is well documented that geographical isolation causes species differentiation in higher life forms and the bellflower species has been extensively studied as a model organism for geological segregation research since it has a high adaptability to divergent environment [12,15]. It has also been reported that the adaptation and flourishing of higher plants in a barren maritime terrain are, to some extent, driven by the symbiotic relationships between soil fungi and plants [16]. ...
Fungal communities in the rhizoplane (RP) and rhizosphere (RS) of geographically isolated C. takesimana habitats in different environments such as oceanic (Seodo, the Dokdo Islands), coastline (Sadong, Ulleungdo Island), and inland (Taeha, Ulleungdo Island) regions were analyzed by MiSeq sequencing. In total, 1279 operational taxonomic units (OTUs) were obtained and they were further classified into 185 genera belonging to five phyla. The total number of fungal taxa in the RP samples was lower than those in the RS samples in all the sampled locations, providing an indication of the existence of a certain level of the selective pressures from the host plant. The richness of the RP in the Dokdo Islands was higher than that of Ulleungdo Island, but the richness of the RS in the Dokdo Islands was lower than that of Ulleungdo Island. These results suggest evidence for strong effects of a harsh geo-climate on the RP and RS fungal diversities in the Dokdo Islands. Additionally, a total of 82 fungal genera were identified in all three RP samples and 63 genera (77%) were uniquely found in each of the geographical regions and 43 genera (52.4%) showed high dependency on the C. takesimana vegetation. It was found that the genus Mortierella was the most dominant taxon in all the samples. The geo-ecological isolation of the Korean bellflower may have caused unique formation of the RP and RS fungal communities in the natural habitats.
... Patterns of morphological diversity do not always represent phylogeny because factors such as local ecological adaptation and phenotypic plasticity can play a role in shaping phenotypic variation e.g. [66], including at the intraspecific level [67][68][69]. To understand evolutionary patterns and processes it can therefore be beneficial to analyze both genetic and morphological data. ...
Background:
Island systems offer excellent opportunities for studying the evolutionary histories of species by virtue of their restricted size and easily identifiable barriers to gene flow. However, most studies investigating evolutionary patterns and processes shaping biotic diversification have focused on more recent (emergent) rather than ancient oceanic archipelagos. Here, we focus on the granitic islands of the Seychelles, which are unusual among island systems because they have been isolated for a long time and are home to a monophyletic radiation of caecilian amphibians that has been separated from its extant sister lineage for ca. 65-62 Ma. We selected the most widespread Seychelles caecilian species, Hypogeophis rostratus, to investigate intraspecific morphological and genetic (mitochondrial and nuclear) variation across the archipelago (782 samples from nine islands) to identify patterns and test processes that shaped their evolutionary history within the Seychelles.
Results:
Overall a signal of strong geographic structuring with distinct northern- and southern-island clusters were identified across all datasets. We suggest that these distinct groups have been isolated for ca. 1.26 Ma years without subsequent migration between them. Populations from the somewhat geographically isolated island of Frégate showed contrasting relationships to other islands based on genetic and morphological data, clustering alternatively with northern-island (genetic) and southern-island (morphological) populations.
Conclusions:
Although variation in H. rostratus across the Seychelles is explained more by isolation-by-distance than by adaptation, the genetic-morphological incongruence for affinities of Frégate H. rostratus might be caused by local adaptation over-riding the signal from their vicariant history. Our findings highlight the need of integrative approaches to investigate fine-scale geographic structuring to uncover underlying diversity and to better understand evolutionary processes on ancient, continental islands.
... This was accomplished using resistance surfaces parameterized as the inverse of predicted habitat suitability (McRae & Beier 2007;Wang et al. 2008;Storfer et al. 2010;Wang et al. 2012;MacDonald et al. 2020). This approach assumes that organisms are more likely to disperse within suitable habitat and experience high resistance when moving through unsuitable habitat; large stretches of unsuitable habitat thereby pose significant barriers to dispersal (Coyne & Orr 2004;Crispo et al. 2006;McRae 2006;McRae & Beier 2007;Thorpe et al. 2008Thorpe et al. , 2010Sánchez-Ramírez et al. 2018). We averaged resistance surfaces of the northern and southern S. hesperis lineages to generate a single resistance surface reflecting the probability that dispersing individuals of the two lineages will come into contact that could result in reciprocal gene flow. ...
... Such periods of geographic isolation are 693 unlikely to be unique to these species complexes that are predominantly maintained by 694 behavioral isolation. Recent demographic modeling studies of emblematic adaptive radiations 695 also maintained by divergent natural selection, such as the radiation of cichlid fishes (Meier, 696 Sousa, et al., 2017) or of Caribbean anoles (Thorpe, Surget-Groba, & Johansson, 2010), 697 confirm that geographic isolation favors adaptive processes that can lead to speciation. Yet, in 698 contrast with those well studied cases of ecological radiations, our study in Chorthippus 699 suggests that sexual selection can lead to radiations in the absence of strong divergent natural 700 selection, resulting in cryptic species that are genetically, morphologically and ecologically 701 similar but that otherwise generally behave as good biological species. ...
... Patterns of morphological diversity do not always represent phylogeny because factors such as local ecological adaptation or phenotypic plasticity can play a role in shaping phenotypic variation (e.g. 66), including at the intraspecific level (66)(67)(68). To understand evolutionary patterns and processes it can therefore be beneficial to analyze both genetic and morphological data. ...
... Patterns of morphological diversity do not always represent phylogeny because factors such as local ecological adaptation or phenotypic plasticity can play a role in shaping phenotypic variation (e.g. 66), including at the intraspecific level (66)(67)(68). To understand evolutionary patterns and processes it can therefore be beneficial to analyze both genetic and morphological data. ...
Background: Island systems offer excellent opportunities for studying the evolutionary histories of species by virtue of their restricted size and easily identifiable barriers to gene flow. However, most studies investigating evolutionary patterns and processes shaping biotic diversification have focused on more recent (emergent) rather than ancient oceanic archipelagos. Here, we focus on the granitic islands of the Seychelles, which are unusual among island systems because they have been isolated for a long time and are home to a radiation of caecilian amphibians that have been separated from their extant sister lineage for ca. 65 Ma. We selected the most widespread Seychelles caecilian species, Hypogeophis rostratus , to investigate morphological and genetic (mitochondrial and nuclear) variation across the archipelago (782 samples from nine islands) to identify patterns and test processes that shaped their evolutionary history within the Seychelles.
Results: Overall a signal of strong geographic structuring with distinct northern- and southern-island clusters were identified across all datasets. We suggest that these distinct groups have been isolated for ca. 1.2 Ma years without subsequent migration between them. Populations from the somewhat geographically isolated island of Frégate showed contrasting relationships to other islands based on genetic and morphological data, clustering alternatively with northern-island (genetic) and southern-island (morphological) populations.
Conclusions: Although variation in H. rostratus across the Seychelles is explained more by isolation-by-distance than by adaptation, the genetic-morphological incongruence for affinities of Frégate H. rostratus might be caused by local ecological adaptation over-riding the signal from their vicariant history. Our findings highlight the need to investigate fine-scale geographic structuring to uncover underlying diversity and to better understand evolutionary processes on ancient, continental islands.
... Patterns of morphological diversity do not always represent phylogeny because factors such as local ecological adaptation and phenotypic plasticity can play a role in shaping phenotypic variation [e.g. 66], including at the intraspeci c level [67][68][69]. To understand evolutionary patterns and processes it can therefore be bene cial to analyze both genetic and morphological data. ...
Background: Island systems offer excellent opportunities for studying the evolutionary histories of species by virtue of their restricted size and easily identifiable barriers to gene flow. However, most studies investigating evolutionary patterns and processes shaping biotic diversification have focused on more recent (emergent) rather than ancient oceanic archipelagos. Here, we focus on the granitic islands of the Seychelles, which are unusual among island systems because they have been isolated for a long time and are home to a monophyletic radiation of caecilian amphibians that has been separated from its extant sister lineage for ca. 65 – 62 Ma. We selected the most widespread Seychelles caecilian species, Hypogeophis rostratus, to investigate intraspecific morphological and genetic (mitochondrial and nuclear) variation across the archipelago (782 samples from nine islands) to identify patterns and test processes that shaped their evolutionary history within the Seychelles.
Results: Overall a signal of strong geographic structuring with distinct northern- and southern-island clusters were identified across all datasets. We suggest that these distinct groups have been isolated for ca. 1.26 Ma years without subsequent migration between them. Populations from the somewhat geographically isolated island of Frégate showed contrasting relationships to other islands based on genetic and morphological data, clustering alternatively with northern-island (genetic) and southern-island (morphological) populations.
Conclusions: Although variation in H. rostratus across the Seychelles is explained more by isolation-by-distance than by adaptation, the genetic-morphological incongruence for affinities of Frégate H. rostratus might be caused by local adaptation over-riding the signal from their vicariant history. Our findings highlight the need of integrative approaches to investigate fine-scale geographic structuring to uncover underlying diversity and to better understand evolutionary processes on ancient, continental islands.
... Patterns of morphological diversity do not always represent phylogeny because factors such as local ecological adaptation and phenotypic plasticity can play a role in shaping phenotypic variation [e.g. 66], including at the intraspeci c level [67][68][69]. To understand evolutionary patterns and processes it can therefore be bene cial to analyze both genetic and morphological data. ...
Background: Island systems offer excellent opportunities for studying the evolutionary histories of species by virtue of their restricted size and easily identifiable barriers to gene flow. However, most studies investigating evolutionary patterns and processes shaping biotic diversification have focused on more recent (emergent) rather than ancient oceanic archipelagos. Here, we focus on the granitic islands of the Seychelles, which are unusual among island systems because they have been isolated for a long time and are home to a monophyletic radiation of caecilian amphibians that has been separated from its extant sister lineage for ca. 65 – 62 Ma. We selected the most widespread Seychelles caecilian species, Hypogeophis rostratus, to investigate intraspecific morphological and genetic (mitochondrial and nuclear) variation across the archipelago (782 samples from nine islands) to identify patterns and test processes that shaped their evolutionary history within the Seychelles.
Results: Overall a signal of strong geographic structuring with distinct northern- and southern-island clusters were identified across all datasets. We suggest that these distinct groups have been isolated for ca. 1.26 Ma years without subsequent migration between them. Populations from the somewhat geographically isolated island of Frégate showed contrasting relationships to other islands based on genetic and morphological data, clustering alternatively with northern-island (genetic) and southern-island (morphological) populations.
Conclusions: Although variation in H. rostratus across the Seychelles is explained more by isolation-by-distance than by adaptation, the genetic-morphological incongruence for affinities of Frégate H. rostratus might be caused by local adaptation over-riding the signal from their vicariant history. Our findings highlight the need of integrative approaches to investigate fine-scale geographic structuring to uncover underlying diversity and to better understand evolutionary processes on ancient, continental islands.
