Driven by the West Wind Drift? A synthesis of southern temperate marine biogeography,with new directions for dispersalism

Aim Twentieth century biogeographers developed intriguing hypotheses involving West Wind Drift dispersal of Southern Hemisphere biota, but such models were largely abandoned in favour of vicariance following the development of plate tectonic theory. Here I present a synthesis of southern temperate marine biogeography, and suggest some new directions for phylogeographic research. Location The southern continents, formerly contiguous components of Gondwana, are now linked only by ocean currents driven by the West Wind Drift. Methods While vicariance theory certainly facilitates the development of testable hypotheses, it does not necessarily follow that vicariance explains much of contemporary southern marine biogeography. To overcome the limitations of narratives that simply assume vicariance or dispersal, it is essential for analyses to test biogeographic hypotheses by incorporating genetic, ecological and geological data. Results Recent molecular studies have provided strong evidence for dispersal, but relatively little evidence for the biogeographic role of plate tectonics in distributing southern marine taxa. Despite confident panbiogeographic claims to the contrary, molecular and ecological studies of buoyant macroalgae, such as Macrocystis, indicate that dispersal predominates. Ironically, some of the better supported evidence for marine vicariance in southern waters has little or nothing to do with plate tectonics. Rather, it involves far more localized and recent vicariant models, such as the isolating effect of the Bassian Isthmus during Pleistocene low sea‐level stands (Nerita). Main conclusions Recent phylogeographic studies of southern marine taxa (e.g. Diloma and Parvulastra) imply that passive rafting cannot be ignored as an important mechanism of long‐distance dispersal. I outline a new direction for southern hemisphere phylogeography, involving genetic analyses of bull‐kelp (Durvillaea) and its associated holdfast invertebrate communities.     

Insights into historical drainage evolution based on the phylogeography of the chevron snakehead fish (Channa striata) in the Mekong Basin

1. The phylogeography of freshwater taxa is often integrally linked with landscape changes such as drainage re‐alignments that may present the only avenue for historical dispersal for these taxa. Classical models of gene flow do not account for landscape changes and so are of little use in predicting phylogeography in geologically young freshwater landscapes. When the history of drainage formation is unknown, phylogeographical predictions can be based on current freshwater landscape structure, proposed historical drainage geomorphology, or from phylogeographical patterns of co‐distributed taxa. 2. This study describes the population structure of a sedentary freshwater fish, the chevron snakehead (Channa striata), across two river drainages on the Indochinese Peninsula. The phylogeographical pattern recovered for C. striata was tested against seven hypotheses based on contemporary landscape structure, proposed history and phylogeographical patterns of co‐distributed taxa. 3. Consistent with the species ecology, analysis of mitochondrial and microsatellite loci revealed very high differentiation among all sampled sites. A strong signature of historical population subdivision was also revealed within the contemporary Mekong River Basin (MRB). Of the seven phylogeographical hypotheses tested, patterns of co‐distributed taxa proved to be the most adequate for describing the phylogeography of C. striata. 4. Results shed new light on SE Asian drainage evolution, indicating that the Middle MRB probably evolved via amalgamation of at least three historically independent drainage sections and in particular that the Mekong River section centred around the northern Khorat Plateau in NE Thailand was probably isolated from the greater Mekong for an extensive period of evolutionary time. In contrast, C. striata populations in the Lower MRB do not show a phylogeographical signature of evolution in historically isolated drainage lines, suggesting drainage amalgamation has been less important for river landscape formation in this region.     

Towards a panbiogeography of the seas

A contrast is drawn between the concept of speciation favoured in the Darwin–Wallace biogeographic paradigm (founder dispersal from a centre of origin) and in panbiogeography (vicariance or allopatry). Ordinary ecological dispersal is distinguished from founder dispersal. A survey of recent literature indicates that ideas on many aspects of marine biology are converging on a panbiogeographic view. Panbiogeographic conclusions supported in recent work include the following observations: fossils give minimum ages for groups and most taxa are considerably older than their earliest known fossil; Pacific/Atlantic divergence calibrations based on the rise of the Isthmus of Panama at 3 Ma are flawed; for these two reasons most molecular clock calibrations for marine groups are also flawed; the means of dispersal of taxa do not correlate with their actual distributions; populations of marine species may be closed systems because of self‐recruitment; most marine taxa show at least some degree of vicariant differentiation and vicariance is surprisingly common among what were previously assumed to be uniform, widespread taxa; mangrove and seagrass biogeography and migration patterns in marine taxa are best explained by vicariance; the Indian Ocean and the Pacific Ocean represent major biogeographic regions and diversity in the Indo‐Australian Archipelago is related to Indian Ocean/Pacific Ocean vicariance; distribution in the Pacific is not the result of founder dispersal; distribution in the south‐west Pacific is accounted for by accretion tectonics which bring about distribution by accumulation and juxtaposition of communities; tectonic uplift and subsidence can directly affect vertical distribution of marine communities; substantial parallels exist between the biogeography of terrestrial and marine taxa; biogeographically and geologically composite areas are tractable using panbiogeographic analysis; metapopulation models are more realistic than the mainland/island dispersal models used in the equilibrium theory of island biogeography; and regional biogeography is a major determinant of local community composition. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 675–723.     

The Casiquiare river acts as a corridor between the Amazonas and Orinoco river basins: biogeographic analysis of the genus Cichla

The Casiquiare River is a unique biogeographic corridor between the Orinoco and Amazonas basins. We investigated the importance of this connection for Neotropical fishes using peacock cichlids (Cichla spp.) as a model system. We tested whether the Casiquiare provides a conduit for gene flow between contemporary populations, and investigated the origin of biogeographic distributions that span the Casiquiare. Using sequences from the mitochondrial control region of three focal species (C. temensis, C. monoculus, and C. orinocensis) whose distributions include the Amazonas, Orinoco, and Casiquiare, we constructed maximum likelihood phylograms of haplotypes and analyzed the populations under an isolation‐with‐migration coalescent model. Our analyses suggest that populations of all three species have experienced some degree of gene flow via the Casiquiare. We also generated a mitochondrial genealogy of all Cichla species using >2000 bp and performed a dispersal‐vicariance analysis (DIVA) to reconstruct the historical biogeography of the genus. This analysis, when combined with the intraspecific results, supports two instances of dispersal from the Amazonas to the Orinoco. Thus, our results support the idea that the Casiquiare connection is important across temporal scales, facilitating both gene flow and the dispersal and range expansion of species.     

Chloroplast evidence for geographic stasis of the Australian bird‐dispersed shrub Tasmannia lanceolata (Winteraceae)

Few chloroplast‐based genetic studies have been undertaken for plants of mesic temperate forests in the southern hemisphere and fossil‐based models have provided evidence of vegetation history only at the broadest scales in this region. This study investigates the chloroplast DNA phylogeography of Tasmannia lanceolata (Winteraceae), a fleshy‐fruited, bird‐dispersed shrub that is widespread in the mountains of southeastern Australia and Tasmania. Thirty haplotypes were identified after sequencing 3206 bp of chloroplast DNA in each of 244 individuals collected across the species’ range. These haplotypes showed unexpectedly strong phylogeographic structuring, including a phylogeographic break within a continuous part of the species’ range, with the distribution of four major clades mostly not overlapping, and geographic structuring of haplotypes within these clades. This strong geographic patterning of chloroplast DNA provided evidence for the survival of T. lanceolata in multiple putative wet forest refugia as well as evidence for additional wet forest species refugia in southeastern Australia. In western Tasmania lower haplotype diversity below the LGM tree line compared to above the LGM tree line suggests that glacial refugia at high altitudes may have been important for T. lanceolata. The level of geographic structuring in T. lanceolata is similar to gravity dispersed southern hemisphere plants such as Nothofagus and Eucalyptus. Behavioural traits of the birds transporting seed may have had a strong bearing on the limited transport of T. lanceolata seed, although factors limiting establishment, possibly including selection, may also have been important.     

Phylogeography and biogeography of the lower Central American Neotropics: diversification between two continents and between two seas

Lower Central America (LCA) provides a geologically complex and dynamic, richly biodiverse model for studying the recent assembly and diversification of a Neotropical biota. Here, we review the growing literature of LCA phylogeography studies and their contribution to understanding the origins, assembly, and diversification of the LCA biota against the backdrop of regional geologic and climatic history, and previous biogeographical inquiry. Studies to date reveal that phylogeographical signal within taxa of differing distributions reflects a diversity of patterns and processes rivalling the complexities of LCA landscapes themselves. Even so, phylogeography is providing novel insights into regional diversification (e.g. cryptic lineage divergences), and general evolutionary patterns are emerging. Congruent multi‐taxon phylogeographic breaks are found across the Nicaraguan depression, Chorotega volcanic front, western and central Panama, and the Darién isthmus, indicating that a potentially shared history of responses to regional‐scale (e.g. geological) processes has shaped the genetic diversity of LCA communities. By contrast, other species show unique demographic histories in response to overriding historical events, including no phylogeographic structure at all. These low‐structure or incongruent patterns provide some evidence for a role of local, ecological factors (e.g. long‐distance dispersal and gene flow in plants and bats) in shaping LCA communities. Temporally, comparative phylogeographical structuring reflects Pliocene–Pleistocene dispersal and vicariance events consistent with the timeline of emergence of the LCA isthmus and its major physiographic features, e.g. cordilleras. We emphasise the need to improve biogeographic inferences in LCA through in‐depth comparative phylogeography projects capitalising on the latest statistical phylogeographical methods. While meeting the challenges of reconstructing the biogeographical history of this complex region, phylogeographers should also take up the critical service to society of applying their work to the conservation of its fascinating biodiversity.     

Pliocene climatic change in insular Southeast Asia as an engine of diversification in Ficedula flycatchers

Aims Insular Southeast Asia and adjacent regions are geographically complex, and were dramatically affected by both Pliocene and Pleistocene changes in climate, sea level and geology. These circumstances allow the testing of several biogeographical hypotheses regarding species distribution patterns and phylogeny. Avian species in this area present a challenge to biogeographers, as many are less hindered by barriers that may block the movements of other species. Widely distributed Southeast Asian avian lineages, of which there are many, have been generally neglected. Ficedula flycatchers are distributed across Eurasia, but are most diverse within southern Asia and Southeast Asian and Indo‐Australian islands. We tested the roles of vicariance, dispersal and the evolution of migratory behaviours as mechanisms of speciation within the Ficedula flycatchers, with a focus on species distributed in insular Southeast Asia. Methods Using a published molecular phylogeny of Ficedula flycatchers, we reconstructed ancestral geographical areas using dispersal vicariance analysis, weighted ancestral area analysis, and a maximum likelihood method. We evaluated the evolution of migratory behaviours using maximum likelihood ancestral character state reconstruction. Speciation timing estimates were calculated via local molecular clock methods. Results Ficedula originated in southern mainland Asia, c. 6.5 Ma. Our analyses indicate that two lineages within Ficedula independently and contemporaneously colonized insular Southeast Asia and Indo‐Australia, c. 5 Ma. The potential impact of vicariance due to rising sea levels is difficult to assess in these early colonization events because the ancestral areas to these clades are reconstructed as oceanic islands. Within each of these clades, inter‐island dispersal was critical to species’ diversification across oceanic and continental islands. Furthermore, Pliocene and Pleistocene climatic change may have caused the disjunct island distributions between several pairs of sister taxa. Both vicariance and dispersal shaped the distributions of continental species. Main conclusions This study presents the first evaluation, for Ficedula, of the importance of vicariance and dispersal in shaping distributions, particularly across insular Southeast Asia and Indo‐Australia. Although vicariant speciation may have initially separated the island clades from mainland ancestors, speciation within these clades was driven primarily by dispersal. Our results contribute to the emerging body of literature concluding that dynamic geological processes and climatic change throughout the Pliocene and Pleistocene have been important factors in faunal diversification across continental and oceanic islands.     

BIOGEOGRAPHY OF A WIDESPREAD FRESHWATER CRUSTACEAN: PSEUDOCONGRUENCE AND CRYPTIC ENDEMISM IN THE NORTH AMERICAN DAPHNIA LAEVIS COMPLEX

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.     

Patterns of population differentiation in annual killifishes from the Paraná–Uruguay–La Plata Basin: the role of vicariance and dispersal

Aim To elucidate the role of vicariance versus dispersal at the microevolutionary scale in annual killifish populations belonging to the Austrolebias bellottii species complex (Rivulidae). Within this complex, A. bellottii and A. apaii have low vagility and occur widely within the study area, making them excellent models for testing biogeographic hypotheses of differentiation. Location South America, in the Paraná–Uruguay–La Plata river basin. Methods Molecular data and morphometric analyses were used to reconstruct the phylogeographic history and morphological variation of 24 populations of two taxa of the A. bellottii species complex. Phylogenetic analyses using maximum likelihood (ML) and Bayesian inference (BI) model‐based methods, estimates of clade divergence times implemented in beast , non‐metric multidimensional scaling, analysis of molecular variance results, and morphological analyses elucidated the role of vicariance versus dispersal hypotheses in population differentiation in the aforementioned river basin. Results In the A. bellottii species complex from the Paraná–Uruguay–La Plata river basin, past allopatric fragmentation from vicariance events seems to be the most plausible scenario for diversification since the Late Miocene and more recently since the Plio‐Pleistocene. The Plio‐Pleistocene vicariance produced the differentiation of three major clades in A. bellottii populations. One clade from the eastern Uruguay River drainage was separated from another in western Uruguay and the Paraná–La Plata River drainages. A later vicariance event split populations to the south (lower Paraná–La Plata Basin) and north (middle Paraná) of the western Paraná River drainage. However, our results do not exclude the possibility of dispersal events among A. bellottii populations from both the Uruguay and Paraná river drainages, which could occur in these river basins during hypothesized connectivity cycles of the Late Pliocene and Pleistocene. Main conclusions Past allopatric fragmentation caused by different vicariance events seems to be the main driver of diversification in the A. bellottii species complex since the Plio‐Pleistocene. However, the current molecular data suggest that populations from both drainages of the Paraná–Uruguay rivers may have experienced cycles of connectivity during the Pleistocene, perhaps including multiple vicariance or dispersal events from populations located in the western lower Uruguay River drainage, which encompassed climatic and geological changes in the Paraná–Uruguay–La Plata Basin.     

Phylogeography of a pearl oyster (Pinctada maxima) across the Indo‐Australian Archipelago: evidence of strong regional structure and population expansions but no phylogenetic breaks

This study investigates the genetic structure and phylogeography of a broadcast spawning bivalve mollusc, Pinctada maxima, throughout the Indo‐West Pacific and northern Australia. DNA sequence variation of the mitochondrial cytochrome oxidase subunit I (COI) gene was analysed in 367 individuals sampled from nine populations across the Indo‐West Pacific. Hierarchical AMOVA indicated strong genetic structuring amongst populations (Φ_ST = 0.372, P < 0.001); however, sequence divergence between the 47 haplotypes detected was low (maximum 1.8% difference) and no deep phylogenetic divergence was observed. Results suggest the presence of genetic barriers isolating populations of the South China Sea and central Indonesian regions, which, in turn, show patterns of historical separation from northern Australian regions. In P. maxima, historical vicariance during Pleistocene low sea levels is likely to have restricted planktonic larval transport, causing genetic differentiation amongst populations. However, low genetic differentiation is observed where strong ocean currents are present and is most likely due to contemporary larval transport along these pathways. Geographical association with haplotype distributions may indicate signs of early lineage sorting arising from historical population separations, yet an absence of divergent phylogenetic clades related to geography could be the consequence of periodic pulses of high genetic exchange. We compare our results with previous microsatellite DNA analysis of these P. maxima populations, and discuss implications for future conservation management of this species. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 632–646.     

DISCORDANT DISTRIBUTION OF POPULATIONS AND GENETIC VARIATION IN A SEA STAR WITH HIGH DISPERSAL POTENTIAL

Patiria miniata, a broadcast‐spawning sea star species with high dispersal potential, has a geographic range in the intertidal zone of the northeast Pacific Ocean from Alaska to California that is characterized by a large range gap in Washington and Oregon. We analyzed spatial genetic variation across the P. miniata range using multilocus sequence data (mtDNA, nuclear introns) and multilocus genotype data (microsatellites). We found a strong phylogeographic break at Queen Charlotte Sound in British Columbia that was not in the location predicted by the geographical distribution of the populations. However, this population genetic discontinuity does correspond to previously described phylogeographic breaks in other species. Northern populations from Alaska and Haida Gwaii were strongly differentiated from all southern populations from Vancouver Island and California. Populations from Vancouver Island and California were undifferentiated with evidence of high gene flow or very recent separation across the range disjunction between them. The surprising and discordant spatial distribution of populations and alleles suggests that historical vicariance (possibly caused by glaciations) and contemporary dispersal barriers (possibly caused by oceanographic conditions) both shape population genetic structure in this species.     

Contrasting diversity and demographic signals in sympatric narrow‐range endemic shrubs of the south‐west Western Australian semi‐arid zone

Comparative studies of sympatric species that integrate both phylogeographical and population genetic approaches provide insight into how demographic events and life history traits shape adaptive potential and drive species persistence. Such studies are rare for species‐rich and strongly structured environments, especially those of the southern hemisphere. For two sympatric, perennial shrubs of the south‐west Western Australian semi‐arid zone, Grevillea globosa and Mirbelia sp. Bursarioides, we assessed historical and contemporary genetic diversity and structure, demographic processes and ratios of pollen to seed dispersal. Phylogeographical structure was not detected and haplotype networks were star‐like. Number of haplotypes, nucleotide diversity, haplotype diversity, and allelic diversity were statistically significantly lower for G. globosa than for M. sp. Bursarioides. Levels of haplotype divergence and more contemporary genetic divergence and expected heterozygosity were lower for G. globosa than for M. sp. Bursarioides, but differences were not statistically significant. Both species exhibited signals of isolation by distance and low pollen to seed dispersal ratios (5.26:1 and 6.88:1). Grevillea globosa displayed signals of historical and contemporary demographic expansion. Results imply an important role for aspects of seed ecology that impact population demography, as well as direct dispersal and a significant contribution of seed dispersal to genetic connectivity in a semi‐arid landscape.     

Genetic structuring in the freshwater mussel Anodonta corresponds with major hydrologic basins in the western United States

Freshwater mussels (unionids) are increasingly recognized as important providers of ecosystem services, yet are among the most endangered fauna in the world. Because unionids are generally sessile and require specific fish hosts for development and dispersal, they are particularly vulnerable to habitat degradation. Surprisingly, little is known about the distribution of genetic diversity in freshwater mussels and this gap has a negative impact on taxonomy, monitoring, conservation and ecological research in these species. Here, we focus on western North American Anodonta, one of only three genera known to exist in this broad landscape and which contains three highly divergent lineages. We describe phylogeographical subdivision in the most widespread and diverse of these lineages, which includes Anodonta californiensis and Anodonta nuttalliana and occurs from Canada to Mexico. Using mitochondrial and nuclear data, we found that genetic structuring within this clade is inconsistent with morphologically based species designations, but instead follows patterns of vicariance among major hydrogeologic basins. Furthermore, there was a strong tendency for population diversity within drainage systems to increase downstream, implying greater habitat or host fish availability in this direction. Microsatellite results indicated that sampling locations were all genetically distinct, even at short distances. Many of our sample populations showed evidence of a recent demographic bottleneck, although this effect seemed to be very local and not drainage or basin‐specific. This study provides a foundation for the establishment of appropriate management units and future research on adaptive differentiation and host fish relationships.     

Phylogenetic relationships of North American nymphophiline gastropods based on mitochondrial DNA sequences

Phylogenetic relationships of 36 nymphophiline species representing 10 genera were inferred from mtCOI sequence data and compared to recent morphology-based classifications of this group. Parsimony and maximum likelihood analyses of the molecular data set suggested monophyly of the North American nymphophilines and a sister or otherwise close relationship between this fauna and a European species assigned to the subfamily. Results also supported a previously hypothesized close relationship between the predominantly freshwater nymphophilines and the brackish-water genus Hydrobia . Our analyses resolved a North American nymphophiline subclade composed of Floridobia , Nymphophilus , and Pyrgulopsis , and depicted the remaining North American genera ( Cincinnatia , Marstonia , Notogillia , Rhapinema , Spilochlamys , Stiobia ) as either a monophyletic or paraphyletic group. Two of the large North American genera ( Floridobia , Marstonia ) were supported as monophyletic groups while monophyly of Pyrgulopsis , a western North American group containing > 100 species, was equivocal. North American nymphophiline phylogeny implies that vicariance of eastern and western North American groups was followed by a secondary invasion of eastern coastal areas from the west. We attribute this to dispersal of salt-tolerant progenitors along the Gulf of Mexico coast     

Environmental DNA phylogeography: Successful reconstruction of phylogeographic patterns of multiple fish species from cups of water

Phylogeography is an integrative field of science linking micro- and macro-evolutionary processes, contributing to the inference of vicariance, dispersal, speciation, and other population-level processes. Phylogeographic surveys usually require considerable effort and time to obtain numerous samples from many geographical sites covering the distribution range of target species; this associated high cost limits their application. Recently, environmental DNA (eDNA) analysis has been useful not only for detecting species but also for assessing genetic diversity; hence, there has been growing interest in its application to phylogeography. As the first step of eDNA-based phylogeography, we examined (1) data screening procedures suitable for phylogeography and (2) whether the results obtained from eDNA analysis accurately reflect known phylogeographic patterns. For these purposes, we performed quantitative eDNA metabarcoding using group-specific primer sets in five freshwater fish species belonging to two taxonomic groups from a total of 94 water samples collected from western Japan. As a result, three-step data screening based on the DNA copy number of each haplotype detected successfully eliminated suspected false positive haplotypes. Furthermore, eDNA analysis could almost perfectly reconstruct the phylogenetic and phylogeographic patterns obtained for all target species with the conventional method. Despite existing limitations and future challenges, eDNA-based phylogeography can significantly reduce survey time and effort and is applicable for simultaneous analysis of multiple species in single water samples. eDNA-based phylogeography has the potential to revolutionize phylogeography.     

Evolutionary and biogeographic relationships of related Ranunculus taxa: dispersal,vicariance and pseudovicariance as mechanisms of change

Background: The disjunct distribution patterns of a taxon may arise when previously continuous distribution ranges are fragmented. The phenomena of vicariance and dispersal, together with hybridisation as an important source of genetic variation in natural populations, can play an important role for structuring the distribution of taxa.

Aims: We investigated the biogeographical relationships of the Iberian endemic plant Ranunculus angustifolius s.l. by reconstructing ancestral geographical distributions, using a combination of phylogenetic and distributional information.

Methods: Phylogenetic and network analyses of nuclear internal transcribed spacers and plastid sequence data (rpl32-trnL, rps16-trnQ, trnK-matK and ycf6-psbM) were used to infer vicariance and dispersal events.

Results: Phylogenetic and biogeographical analyses suggested that both dispersal and vicariance were important in creating the current disjunct distribution pattern. Some other factors, such as hybridisation, introgression and vicariance (or pseudovicariance), were important in the evolutionary history of the taxa R. angustifolius s.l.

Conclusions: Our results demonstrate the importance for analysing biogeographical patterns with the use of both nuclear and chloroplast DNA to infer the evolutionary history of plant species with a disjunct distribution. Our results show that phenomena such as dispersal, vicariance and pseudovicariance are not mutually exclusive.     

Consequences of marine barriers for genetic diversity of the coral‐specialist yellowbar angelfish from the Northwestern Indian Ocean

Ocean circulation, geological history, geographic distance, and seascape heterogeneity play an important role in phylogeography of coral‐dependent fishes. Here, we investigate potential genetic population structure within the yellowbar angelfish (Pomacanthus maculosus) across the Northwestern Indian Ocean (NIO). We then discuss our results with respect to the above abiotic features in order to understand the contemporary distribution of genetic diversity of the species. To do so, restriction site‐associated DNA sequencing (RAD‐seq) was utilized to carry out population genetic analyses on P. maculosus sampled throughout the species’ distributional range. First, genetic data were correlated to geographic and environmental distances, and tested for isolation‐by‐distance and isolation‐by‐environment, respectively, by applying the Mantel test. Secondly, we used distance‐based and model‐based methods for clustering genetic data. Our results suggest the presence of two putative barriers to dispersal; one off the southern coast of the Arabian Peninsula and the other off northern Somalia, which together create three genetic subdivisions of P. maculosus within the NIO. Around the Arabian Peninsula, one genetic cluster was associated with the Red Sea and the adjacent Gulf of Aden in the west, and another cluster was associated with the Arabian Gulf and the Sea of Oman in the east. Individuals sampled in Kenya represented a third genetic cluster. The geographic locations of genetic discontinuities observed between genetic subdivisions coincide with the presence of substantial upwelling systems, as well as habitat discontinuity. Our findings shed light on the origin and maintenance of genetic patterns in a common coral reef fish inhabiting the NIO, and reinforce the hypothesis that the evolution of marine fish species in this region has likely been shaped by multiple vicariance events.     

The Central American Isthmus: Implications for Intraspecific Phylogeny and Biogeography of a Pantropical Green Alga

An intraspecific phylogenetic study was undertaken to resolve the evolutionary relationship of isolates of the green alga Phyllodictyon anastomosans (Harv.) Kraft et Wynne that occur on Atlantic and Pacific coasts of the Central American Isthmus. Patterns of vicariance related to the emergence of the Central American Isthmus were evident, but numerous examples of recent trans‐oceanic and trans‐isthmian dispersal obscured the underlying pattern. This study, one of the first studies to assess the impact of the emergence of the Central American Isthmus in seaweed phylogeography, provided an ideal opportunity to estimate the rate of sequence evolution using a single time point. Using this newly calibrated molecular clock the timing of an historical introduction across the isthmus is shown to be concordant with a shallow water breach of the isthmus dated at approximately 2.3–2.0 million years ago. This work contributes to a growing body of literature that suggests marine algae are fairly successful at dispersing over long distances in recent times.     

Phylogeographic patterns of Merodon hoverflies in the Eastern Mediterranean region: revealing connections and barriers

We investigated the phylogeographic patterns of Merodon species (Diptera, Syrphidae) in the Eastern Mediterranean. Ten species were sampled on five different islands and mainland sites as a minimum. All samples were screened for their mtDNA COI barcode haplotype diversity, and for some samples, we additionally generated genomic fingerprints. The recently established zoogeographic distribution categories classify these species as having (1) Balkan distribution; (2) Anatolian distribution; (3) continental areas and large islands distribution; and (4) with wide distribution. The ancestral haplotypes and their geographical localities were estimated with statistical parsimony (TCS). TCS networks identified as the ancestral haplotype samples that originated from localities situated within the distributional category of the species in question. Strong geographical haplotype structuring was detected for many Merodon species. We were particularly interested to test the relative importance of current (Aegean Sea) and past Mid‐Aegean Trench) barriers to dispersal for Merodon flies in the Aegean. We employed phylogenetic β‐diversity (Pβ_total) and its partition in replacement (Pβ_repl) and richness difference (Pβ_rich) to test the importance of each explanatory variable (interisland distance, MAT, and island area) in interisland differences using partial Mantel tests and hierarchical partitioning of variation. β‐Analyses confirmed the importance of both current and past barriers to dispersal on the evolution of group. Current interisland distance was particularly important to explain the replacement of haplotypes, while the MAT was driving differences in richness of haplotypes, revealing the MAT as a strong past barrier whose effects are still visible today in the phylogenetic history of the clade in the Aegean. These results support the hypothesis of a highly restricted dispersal and gene flow among Merodon populations between islands since late Pleistocene. Additionally, patterns of phylogeographic structure deduced from haplotype connections and ISSR genome fingerprinting data revealed a few putative cases of human‐mediated transfers of Merodon spp.     

Testing for biogeographic mechanisms promoting divergence in Caribbean crickets (genus Amphiacusta)

Aim This work examines whether the history of diversification of Amphiacusta (Orthoptera, Gryllidae) in the Caribbean corresponds to a vicariant or a dispersalist model. Location The Greater Antillean islands of the Caribbean region. Methods The phylogenetic relationships among species were estimated using a procedure that directly estimates the underlying species tree from independent loci (in this case, one mitochondrial and one nuclear locus). This tree was then used to test for topological congruence with a vicariant model, and to estimate divergence times. Results The analyses based on the expected pattern of species divergence (i.e. species‐tree topology) support a vicariant model. With the notable exception of a dispersal event marking the colonization of Jamaica, the timing of the events are generally consistent with a vicariant scenario, given the current taxon sampling and potential errors with dating the divergence events. Main conclusions The tendency of species to co‐segregate by island suggests that intra‐island diversification is common. Despite their flightlessness, species of Amphiacusta are apparently capable of long‐distance dispersal, such as colonization from the Puerto Rican/Virgin Island bank to Jamaica. The topology of the species tree is consistent with a vicariant model of divergence, and the dates of divergence between island groups are generally consistent with an island–island vicariance model. A strict island–island vicariance scenario can, however, be rejected because of inferred dispersal events such as the colonization of Jamaica. Nevertheless, the biogeographic tests suggest that most of the diversity was generated under a combination of intra‐island diversification and island–island vicariance. Additional sampling of taxa will be needed to verify this hypothesized scenario. Our findings indicate that Amphiacusta presents an ideal opportunity for examining the role of sexual selection in promoting diversification, which would complement the large number of studies focused on adaptive divergence of Caribbean taxa.