Riverine Barriers Research Articles

Phylogeography of Silver Pheasant (Lophura nycthemera L.) across China: aggregate effects of refugia, introgression and riverine barriers

The role of Pleistocene glacial cycles in forming the contemporary genetic structure of organisms has been well studied in China with a particular focus on the Tibetan Plateau. However, China has a complex topography and diversity of local climates, and how glacial cycles may have shaped the subtropical and tropical biota of the region remains mostly unaddressed. To investigate the factors that affected the phylogeography and population history of a widely distributed and nondeciduous forest species, we analysed morphological characters, mitochondrial DNA sequences and nuclear microsatellite loci in the Silver Pheasant (Lophura nycthemera). In a pattern generally consistent with phenotypic clusters, but not nominal subspecies, deeply divergent mitochondrial lineages restricted to different geographic regions were detected. Coalescent simulations indicated that the time of main divergence events corresponded to major glacial periods in the Pleistocene and gene flow was only partially lowered by drainage barriers between some populations. Intraspecific cytonuclear discordance was revealed in mitochondrial lineages from Hainan Island and the Sichuan Basin with evidence of nuclear gene flow from neighbouring populations into the latter. Unexpectedly, hybridization was revealed in Yingjiang between the Silver Pheasant and Kalij Pheasant (Lophura leucomelanos) with wide genetic introgression at both the mtDNA and nuclear levels. Our results highlight a novel phylogeographic pattern in a subtropical area generated from the combined effects of climate oscillation, partial drainage barriers and interspecific hybridization. Cytonuclear discordance combined with morphological differentiation implies that complex historical factors shaped the divergence process in this biodiversity hot spot area of southern China.

Escapement, route choice, barrier passage and entrainment of seaward migrating European eel, Anguilla anguilla, within a highly regulated lowland river

Fluvial disconnectivity can have important impacts on fish populations, including hindering movement between habitats required for different ontogenic stages. Recruitment of the European eel (Anguilla anguilla) has reduced by over 90% since the early 1980's, in part due to the effect of riverine barriers on its catadromous migration. There is a legislative requirement to restore free passage, increase habitat availability, and limit anthropogenic losses at intakes to aid eel recovery and good ecological status; necessitating an improved understanding of underlying processes. Escapement, route choice, delay at structures, and entrainment at water abstraction points of downstream migrating silver eels were examined using acoustic and Passive Integrated Transponder (PIT) telemetry in the heavily regulated lower river Stour, UK. Downstream migrating adult eel (n=69) were trapped approximately 10km upstream of the tidal limit, surgically implanted with an acoustic transducer and PIT transponder, and released between October and December in 2009 and 2010. Movements of tagged individuals were monitored by a linear array of 19 fixed acoustic receivers extending from the release site, through the last 9.2km of the freshwater catchment. Three groups of water control structures, two water abstraction intakes and several possible routes of migration are present in the reach. Seventy six and 65% of tagged eels escaped from the study reach in 2009 and 2010, respectively. Entrainment at a single intake was the principal cause of loss and positively related to rapid increases in abstraction whilst eels were in the vicinity of the intake. Route choice into the estuary was dependent on discharge over a large intertidal weir; opening regimes of a tidal gate at the termination of the alternative channel; and abstraction rate at a nearby water intake. Long delays (up to 68.5 days) and recurrent behaviour were associated with several structures in the study reach; high variability between individuals reflected the management of spill at weirs. Potential scenarios for minimising entrainment and delay through integrated management of water level control structures and abstraction rates are discussed.

Testing the Role of Meander Cutoff in Promoting Gene Flow across a Riverine Barrier in Ground Skinks (Scincella lateralis)

Despite considerable attention, the long-term impact of rivers on species diversification remains uncertain. Meander loop cutoff (MLC) is one river phenomenon that may compromise a river’s diversifying effects by passively transferring organisms from one side of the river to the other. However, the ability of MLC to promote gene flow across rivers has not been demonstrated empirically. Here, we test several predictions of MLC-mediated gene flow in populations of North American ground skinks (Scincella lateralis) separated by a well-established riverine barrier, the Mississippi River: 1) individuals collected from within meander cutoffs should be more closely related to individuals across the river than on the same side, 2) individuals within meander cutoffs should contain more immigrants than individuals away from meander cutoffs, 3) immigration rates estimated across the river should be highest in the direction of the cutoff event, and 4) the distribution of alleles native to one side of the river should be better predicted by the historical rather than current path of the river. To test these predictions we sampled 13 microsatellite loci and mitochondrial DNA from ground skinks collected near three ancient meander loops. These predictions were generally supported by genetic data, although support was stronger for mtDNA than for microsatellite data. Partial support for genetic divergence of samples within ancient meander loops also provides evidence for the MLC hypothesis. Although a role for MLC-mediated gene flow was supported here for ground skinks, the transient nature of river channels and morphologies may limit the long-term importance of MLC in stemming population divergence across major rivers.

Genetic Structure of Wild Bonobo Populations: Diversity of Mitochondrial DNA and Geographical Distribution

Bonobos (Pan paniscus) inhabit regions south of the Congo River including all areas between its southerly tributaries. To investigate the genetic diversity and evolutionary relationship among bonobo populations, we sequenced mitochondrial DNA from 376 fecal samples collected in seven study populations located within the eastern and western limits of the species’ range. In 136 effective samples from different individuals (range: 7–37 per population), we distinguished 54 haplotypes in six clades (A1, A2, B1, B2, C, D), which included a newly identified clade (D). MtDNA haplotypes were regionally clustered; 83 percent of haplotypes were locality-specific. The distribution of haplotypes across populations and the genetic diversity within populations thus showed highly geographical patterns. Using population distance measures, seven populations were categorized in three clusters: the east, central, and west cohorts. Although further elucidation of historical changes in the geological setting is required, the geographical patterns of genetic diversity seem to be shaped by paleoenvironmental changes during the Pleistocene. The present day riverine barriers appeared to have a weak effect on gene flow among populations, except for the Lomami River, which separates the TL2 population from the others. The central cohort preserves a high genetic diversity, and two unique clades of haplotypes were found in the Wamba/Iyondji populations in the central cohort and in the TL2 population in the eastern cohort respectively. This knowledge may contribute to the planning of bonobo conservation.

River barriers and cryptic biodiversity in an evolutionary museum.

The Riverine Barriers Hypothesis (RBH) posits that tropical rivers can be effective barriers to gene flow, based on observations that range boundaries often coincide with river barriers. Over the last 160 years, the RBH has received attention from various perspectives, with a particular focus on vertebrates in the Amazon Basin. To our knowledge, no molecular assessment of the RBH has been conducted on birds in the Afrotropics, despite its rich avifauna and many Afrotropical bird species being widely distributed across numerous watersheds and basins. Here, we provide the first genetic evidence that an Afrotropical river has served as a barrier for birds and for their lice, based on four understory bird species collected from sites north and south of the Congo River. Our results indicate near-contemporaneous, Pleistocene lineage diversification across the Congo River in these species. Our results further indicate differing levels of genetic variation in bird lice; the extent of this variation appears linked to the life-history of both the host and the louse. Extensive cryptic diversity likely is being harbored in Afrotropical forests, in both understory birds and their lice. Therefore, these forests may not be “museums” of old lineages. Rather, substantial evolutionary diversification may have occurred in Afrotropical forests throughout the Pleistocene, supporting the Pleistocene Forest Refuge Hypothesis. Strong genetic variation in birds and their lice within a small part of the Congo Basin forest indicates that we may have grossly underestimated diversity in the Afrotropics, making these forests home of substantial biodiversity in need of conservation.

Taxonomy of the South American Dwarf Boas of the Genus Tropidophis Bibron, 1840, With the Description of Two New Species from the Atlantic Forest (Serpentes: Tropidophiidae)

A taxonomic study on the South American dwarf boas of the genus Tropidophis revealed the existence of two new species in the Atlantic Forest biome. As a result, we recognize five mainland species, three in the Atlantic Forest and two in northwestern South America. Based on general distribution and morphological orientation, the type locality of T. paucisquamis is restricted to Estação Biológica de Boracéia (EBB), municipality of Salesópolis, state of São Paulo, Brazil; furthermore, a lectotype for T. taczanowskyi is designated. We provide data on the hemipenial morphology of two South American Tropidophis, showing that the quadrifurcate condition described for West Indian taxa also occurs in mainland congeners. The distributions of the three Atlantic Forest species are congruent with patterns of diversification of other vertebrate taxa associated with cold climates prevalent at high elevations. Refugial isolation and riverine barriers may account for such speciation events.

Role of environmental, historical and spatial processes in the structure of Neotropical primate communities: contrasting taxonomic and phylogenetic perspectives

AbstractAimTo evaluate relative importance of niche, historical and spatial processes on the taxonomic and phylogenetic structure of primate communities.LocationNeotropics.MethodsData on community composition for 74 sites were gathered from the literature. Communities were characterized based on taxonomic and phylogenetic composition. Three predictive matrices were used as explanatory variables representing ecological (environmental), historical (riverine barriers and Pleistocene refugia) and dispersal‐based spatial hypotheses (spatial principal coordinates of neighbour matrices vectors based on geographic coordinates). Variation partitioning analyses were used to decouple independent and shared effects. Permutation procedures based on redundancy analysis were used to determine if explained variation was statistically significant.ResultsForty‐nine per cent of variation in taxonomic structure and 66% of variation in phylogenetic structure was explained by selected predictor variables. Independent effects of spatial variables explained the largest portion of variation in both diversity metrics. Fractions representing shared effects of historical and spatial variables, and of all variables combined, were also large and significant. Independent effects of environmental and historical variables were small to non‐existent (< 4%). When analysing each phylogenetic metric independently the relative contributions of shared fractions changed, although the independent spatial fraction remained the most important predictor.Main conclusionsOur results show that purely spatial processes, such as dispersal limitation, may play a stronger role in structuring primate communities than niche mechanisms and historical events. Furthermore, we find that the influence of ecological and evolutionary mechanisms is conflated with spatial processes, suggesting that community structure is determined jointly by spatial mechanisms reflecting environmental gradients and biogeographical processes. Although the relative contributions of each predictor variable were similar between taxonomic and phylogenetic metrics, a deeper examination of phylogenetic metrics suggests that ecological, historical and spatial mechanisms interact in complex ways to determine current patterns of phylogenetic community structure.

Thesis abstract: Orang-utan genes in space and time: the impact of evolutionary processes of diversification on Bornean orang-utans

The evolutionary processes driving patterns of genetic diversity and differentiation, and ultimately leading to speciation, are poorly understood. The aim of this thesis was to investigate the effects of environmental and biological mechanisms on gene flow and genetic diversity in the Bornean orang-utans, Specifically, I examined the effects of the Pleistocene climatic changes and riverine barriers as well as sex-biased dispersal. My results suggest that current Bornean orang-utan populations are the result of a recent radiation throughout the island, following the probable confinement within a glacial refugium in the Pleistocene. Furthermore, I found evidence for an extreme pattern of female philopatry and male-biased dispersal. These processes have led to highly structured genetic diversity, rendering the orangutans particularly vulnerable to anthropogenic effects and future climatic changes.

Deep Phylogeographic Structure and Environmental Differentiation in the Carnivorous Plant Sarracenia alata

We collected ~29 kb of sequence data using Roche 454 pyrosequencing in order to estimate the timing and pattern of diversification in the carnivorous pitcher plant Sarracenia alata. Utilizing modified protocols for reduced representation library construction, we generated sequence data from 86 individuals across 10 populations from throughout the range of the species. We identified 76 high-quality and high-coverage loci (containing over 500 SNPs) using the bioinformatics pipeline PRGmatic. Results from a Bayesian clustering analysis indicate that populations are highly structured, and are similar in pattern to the topology of a population tree estimated using *BEAST. The pattern of diversification within Sarracenia alata implies that riverine barriers are the primary factor promoting population diversification, with divergence across the Mississippi River occurring more than 60,000 generations before present. Further, significant patterns of niche divergence and the identification of several outlier loci suggest that selection may contribute to population divergence. Our results demonstrate the feasibility of using next-generation sequencing to investigate intraspecific genetic variation in nonmodel species.

Population genetic structure of a threatened tortoise across the south‐eastern United States: implications for conservation management

AbstractThe progressive loss and fragmentation of longleaf pine forests throughout the southeastern United States has led to severe declines in habitat specialists such as the federally listed gopher tortoise Gopherus polyphemus. However, little is known of the range‐wide historical genetic structure of this species or how habitat loss may have impacted the genetic diversity of this species over time. As genetic data are lacking in many parts of the gopher tortoise range, management of federally listed populations in Louisiana and Mississippi have been based on conservation units delineated by rivers. However, this current management strategy has been formulated without any knowledge of how riverine barriers might relate to genetic population structure. Here, we examine variability of mitochondrial and nuclear microsatellite markers in gopher tortoise populations across their natural range in the southeastern United States. Results from the mitochondrial data showed a historical phylogenetic break that is coincident with the Apalachicola River and a novel population assemblage located within western Georgia. Genetic structure based on microsatellite loci revealed high levels of genetic differentiation in some regions and a pattern of isolation by distance at two spatial scales. We also find that rivers across the federally listed portion of the range, do not significantly influence gene flow. Coalescent analyses of population demographic change in gopher tortoises indicate evidence of an ancient and severe population decline at sites across the range. Findings from this study provide important information that will aid in the identification of distinct population units for management and in the formulation of recommendations for the future maintenance of genetic diversity in this species.

Detecting cryptic speciation in the widespread and morphologically conservative carpet chameleon (Furcifer lateralis) of Madagascar

Species delimitation within recently evolved groups can be challenging because species may be difficult to distinguish morphologically. Following the General Lineage Concept, we apply a multiple evidence approach to assess species limits within the carpet chameleon Furcifer lateralis, which is endemic to Madagascar and exported in large numbers for the pet trade. Cryptic speciation within F. lateralis was considered likely because this species (1) has a vast distribution, (2) occupies exceptionally diverse habitats and (3) exhibits subtle regional differences in morphology. Phylogenetic trees reconstructed using nuclear and mitochondrial genes recovered three well-supported clades corresponding with geography. Morphological results based on canonical variates analysis show that these clades exhibit subtle differences in head casque morphology. Ecological niche modelling results found that these phylogenetic groups also occupy unique environmental space and exhibit patterns of regional endemism typical of other endemic reptiles. Combined, our findings provide diverse yet consistent evidence for the existence of three species. Consequently, we elevate the subspecies F. lateralis major to species rank and name a new species distributed in northern and western Madagascar. Initial ecological divergence, associated with speciation of F. lateralis in humid eastern habitat, fits the Ecographic Constraint model for species diversification in Madagascar. By contrast, the second speciation event provides some support for the Riverine Barrier model, with the Mangoky River possibly causing initial isolation between species. These findings thus support two contrasting models of speciation within closely related species and demonstrate the utility of applying a combined-evidence approach for detecting cryptic speciation.

The influence of riverine barriers on phylogeographic patterns of Malagasy reed frogs (Heterixalus)

We analyzed the influence of large rivers on the phylogeography of endemic widespread amphibians along Madagascar’s east coast, using as models various species and species complexes of Malagasy reed frogs (Heterixalus spp.) that are specialized to either highland or lowland habitats. We assembled a dense sampling across the full species ranges and used mitochondrial (cob) as well as nuclear (Rag-1) DNA sequences to assess their phylogeographies. A multigene mtDNA phylogeny of each species was constructed to establish the relationships among the main phylogroups, in order to understand the geographical regions of clade origins and possible directions of historical range expansions. Distinct intraspecific lineages as diagnosed by mitochondrial haplotype clades were found in highlands and lowlands. Most geographical boundaries among these phylogroups did not coincide with rivers, indicating that the influence of rivers on the primary divergence of phylogroups is probably minor in these frogs. Nevertheless, we found evidence for the influence of one riverine barrier in the lowland species complex, where the most important genetic discontinuity (the border between Heterixalus madagascariensis and H. alboguttatus) coincides with the geographical position of the Mangoro River on Madagascar’s central east coast. Analyses of the highland species H. betsileo revealed the existence of six deep haplotype lineages, separated in two major subpopulations which differ largely in altitudinal distribution and do not overlap with the geographical settings of rivers in the highlands. Furthermore, our analyses indicated that most of the major intraspecific lineages of reed frogs show signs of a rather recent population expansion.

The Role of Physical Barriers in the Location of Avian Suture Zones in the Guiana Shield, Northern Amazonia

Suture zones represent natural forums in which to examine the role of geography and ecology in the speciation process. Here, we conduct a comparative analysis designed to investigate the location of avian phylogeographic breaks and contact zones in the Guiana Shield, northern Amazonia. We use distributional and genetic data from 78 pairs of avian taxa to address whether phylogeographic breaks and contact zones are associated with contemporary landscape features. Using spatially explicit statistical models, we found that phylogeographic breaks and contact zones are not randomly distributed throughout the landscape. In general, geographic breaks cluster along physical barriers (rivers, nonforested habitats, and small mountain ranges), whereas contact zones aggregate where these barriers either break down or are easier to overcome, such as around rivers' headwaters. Our results indicate that although major Amazonian rivers are often key determinants of taxon boundaries, the "riverine barrier effect" is a synergistic consequence of the wide lower reaches of some rivers, coupled with nonriverine landscape features at the headwaters. Our data suggest that ancestral refugia are not necessary to explain current distribution patterns and that pairs of codistributed taxa do not seem to be the result of simultaneous diversification processes.

Role of recent and old riverine barriers in fine-scale population genetic structure of Geoffroy's tamarin (Saguinus geoffroyi) in the Panama Canal watershed.

The role of physical barriers in promoting population divergence and genetic structuring is well known. While it is well established that animals can show genetic structuring at small spatial scales, less well-resolved is how the timing of the appearance of barriers affects population structure. This study uses the Panama Canal watershed as a test of the effects of old and recent riverine barriers in creating population structure in Saguinus geoffroyi, a small cooperatively breeding Neotropical primate. Mitochondrial sequences and microsatellite genotypes from three sampling localities revealed genetic structure across the Chagres River and the Panama Canal, suggesting that both waterways act as barriers to gene flow. F-statistics and exact tests of population differentiation suggest population structure on either side of both riverine barriers. Genetic differentiation across the Canal, however, was less than observed across the Chagres. Accordingly, Bayesian clustering algorithms detected between two and three populations, with localities across the older Chagres River always assigned as distinct populations. While conclusions represent a preliminary assessment of genetic structure of S. geoffroyi, this study adds to the evidence indicating that riverine barriers create genetic structure across a wide variety of taxa in the Panama Canal watershed and highlights the potential of this study area for discerning modern from historical influences on observed patterns of population genetic structure.

Phylogenetic relationship between Callosciurus caniceps andC. inornatus (Rodentia, Sciuridae): Implications for zoogeographical isolation by the Mekong River

To test the riverine barrier hypothesis in small arboreal mammals, we examined phylogenetic relationship between two Callosciurus squirrel species (C. caniceps and C. inornatus) geographically isolated in the northeastern part of the Indochina Peninsula by the Mekong River. We did this by comparing complete mitochondrial DNA cytochrome b gene sequences of these two squirrels and five other Callosciurus species: C. erythraeus, C. finlaysonii, C. nigrovittatus, C. notatus, and C. prevostii. Phylogenetic trees showed that there are three major lineages: (1) a lineage containing C. caniceps, C. erythraeus, C. finlaysonii, and C. inornatus; (2) a C. notatus lineage; and (3) a lineage containing C. nigrovittatus and C. prevostii. Callosciurus caniceps was most closely related to C. inornatus. Based on transversional divergence rate at the third codon position of cytochrome b gene, they diverged about 1.2 million years ago. The drastic eastward shift of the Mekong River may have isolated ancestors of C. caniceps and C. inornatus. Then, these two species might have evolved in the different environments of each side of the Mekong River. This phylogeographic history suggests a typical case of allopatric speciation.

Pliocene diversification within the South American Forest falcons (Falconidae: Micrastur)

The Neotropics are one of the most species rich regions on Earth, with over 3150 species of birds. This unrivaled biodiversity has been attributed to higher proportions of mountain ranges, tropical rain forest or rain fall in the forest than in any other major biogeographic regions. Five primary hypotheses aim to explain processes of diversification within the Neotropics; (1) the Pleistocene refuge hypothesis, (2) the riverine barrier hypothesis, (3) the Miocene marine incursions hypothesis, (4) the ecological gradient hypothesis, and (5) the impact of the last Andean uplift serving as a barrier between eastern and western population Andean populations. We assessed these hypotheses to see which best explained the species richness of the forest-falcons (Micrastur), a poorly known lineage of birds that inhabit lowland and mid-elevation humid forest. Our analyses suggest all speciation events within the genus Micrastur probably occurred in the last 2.5–3.6myrs, at or before the Pliocene/Pleistocene boundary, with the basal split within the genus being 7myrs old. Hence our data allow us to formerly reject the classical Pleistocene refuge for Micrastur, Our divergence time estimates are younger that dates for the Miocene marine incursions, the riverine barrier and the Andean uplift hypotheses.

Current geographical ranges of Malagasy dung beetles are not delimited by large rivers

Aim We investigated whether the largest river (Mangoro) on the east coast of Madagascar acts as a barrier to dispersal in dung beetles by comparing species composition and genetic differentiation of the most common species on the two banks of the river. Moreover, by analysing the current geographical ranges of all wet forest dung beetle species, possible long-term effects of the largest rivers on the distribution of species were assessed. Location Madagascar. Methods Dung beetles were sampled with baited pitfall traps at a downstream and an upstream locality on the two banks of the Mangoro River. The most common species, Nanos binotatus (Canthonini), was sequenced for cytochrome c oxidase subunit I (COI; 804 bp) to characterize within-population diversity and between-population genetic differentiation. For the analysis of species geographical range boundaries in relation to the position of the largest rivers on the east coast, a database including all the records for 158 wet forest species was used. The congruence of species range boundaries with the positions of the rivers was tested with a randomization test. Results All common species were found on both sides of the Mangoro River. In Nanos binotatus, haplotype and nucleotide diversities ranged from 0.25 to 0.85 and 0.001 to 0.01, respectively. Population differentiation was high and significant in all comparisons (P < 0.01; average FST = 0.61). The differentiation was not significantly higher across than along the river, as would be expected by the riverine barrier hypothesis. There was no indication that the range boundaries of wet forest dung beetle species would generally coincide with the largest rivers in eastern Madagascar. Main conclusions The results provide little support for the riverine barrier hypothesis as an explanation for the current range boundaries of dung beetles in eastern Madagascar. However, extensive deforestation of the coastal regions in eastern Madagascar may have caused a great shrinkage of the ranges of many forest-dwelling species. Thus the present-day distributions may not reflect accurately the patterns of the past geographical ranges of the species.

Colonization Process of the Brazilian Common Vesper Mouse, Calomys expulsus (Cricetidae, Sigmodontinae): A Biogeographic Hypothesis

Riverine barriers have been associated to genetic diversification and speciation of several taxa. The Rio São Francisco is one of the largest rivers in South America, representing the third largest river basin in Brazil and operating as a geographic barrier to gene flow of different taxa. To evaluate the influence of the Rio São Francisco in the speciation of small rodents, we investigated the genetic structure of Calomys expulsus with phylogenetic and network analyses of cytochrome b DNA. Our results suggested that C. expulsus can be divided into 3 subpopulations, 2 on the left and another one on the right bank of this river. The time of divergence of these subpopulations, using a Bayesian framework, suggested colonization from the south to the north/northeast. Spatial analysis using a clustering method and the Monmonier's algorithm suggested that the Rio São Francisco is a biogeographic barrier to gene flow and indicated that this river may play a role in the incipient speciation process of these subpopulations.

Skull shape and size variation in Ctenomys minutus (Rodentia: Ctenomyidae) in geographical, chromosomal polymorphism, and environmental contexts

We tested the influence of migration and drift (isolation-by-distance model), and differences in micro-habitat on phenotypic traits, and correlated this with chromosomal polymorphism, at the intraspecific level, with geometric descriptors of the cranium and mandible over the entire range of subterranean rodent Ctenomys minutus. This species occurs in two different environments (dunes and sandy fields), along a strip extending for 470 km on the coastal plain of southern Brazil. Ctenomys minutus has seven parental chromosomal diploid numbers, several intraspecific hybrid zones, and up to 15 different karyotypes structured almost linearly along the coastline. Chromosomal populations show significant overall differences in size and shape, intraspecific hybrids are phenotypically intermediate between parental forms, and clustering suggests four groups delimited by chromosomal inversions and riverine barriers. Dune and field morphologies were significantly different in cranial shape. A significant but weak correlation between morphological and geographic distances along the complete distribution was found, supporting the isolation-by-distance model. The intraspecific phenotypic differences appear to arise as a combination of selection and drift acting as diversifying forces. Chromosomal inversions, rivers, and paleochannels appear to be acting as barriers to gene flow, unlike robertsonian fusions and fissions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 705‐720.

Do diversification models of Madagascar’s biota explain the population structure of the endemic bat Myotis goudoti (Chiroptera: Vespertilionidae)?

Aim Three mechanisms have been proposed to explain the adaptive radiations and species diversifications of Madagascar’s biota: the ecogeographical constraint, the riverine barrier and the micro-endemism models. On the intraspecific level, each model predicts different patterns of gene flow across the island’s physical and ecological features. To evaluate these models, phylogeographical analyses were conducted on a widespread and endemic species of bat, Myotis goudoti (Vespertilionidae). Location Madagascar. Methods In order to reconstruct the phylogeographical history of M. goudoti, the mitochondrial D-loop and the cytochrome b gene were sequenced for 195 bats from 41 localities. Phylogenetic reconstructions and a minimum spanning tree were used to infer haplotype relationships. The effect of barriers on gene flow was evaluated using analyses of molecular variance and pairwise population differentiation. Mismatch distribution and coalescence-based estimates were conducted to infer the demographic history of M. goudoti. Results The sequenced individuals showed 159 distinct D-loop haplotypes, most of them being unique to a single location. Populations were significantly structured (ΦST = 0.170, P < 0.001) across Madagascar, but only a minor part of the overall genetic variance was explained by any of the three models. Shared ancestry of lineages across most physical or ecological barriers was common, whereas the uncovered genetic differences between southern and central-northern populations were unexpected. Main conclusions Major barriers predicted by the three biogeographical models do not explain the segregation of mitochondrial lineages of M. goudoti across Madagascar. This is not simply attributable to the high dispersal ability of this species, as populations are notably structured. The genetic contrast between southern and central-northern populations, separated by a zone of admixture, suggests that these areas currently support populations that expanded during the Late Pleistocene. This latitudinal differentiation of populations has been observed in less vagile animals, such as geckos and lemurs, suggesting that climate fluctuations of the Pleistocene had an impact across several groups and resulted in northern and southern refugia in Madagascar.