Overwater Dispersal Research Articles

Molecular phylogeny and biogeography of the temperate Gondwanan family Triaenonychidae (Opiliones : Laniatores) reveals pre-Gondwanan regionalisation, common vicariance, and rare dispersal

Triaenonychidae Sørensen in L. Koch, 1886 is a large family of Opiliones with ~480 described species broadly distributed across temperate forests in the Southern Hemisphere. However, it remains poorly understood taxonomically, as no comprehensive phylogenetic work has ever been undertaken. In this study we capitalise on samples largely collected by us during the last two decades and use Sanger DNA-sequencing techniques to produce a large phylogenetic tree with 300 triaenonychid terminals representing nearly 50% of triaenonychid genera and including representatives from all the major geographic areas from which they are known. Phylogenetic analyses using maximum likelihood and Bayesian inference methods recover the family as diphyletic, placing Lomanella Pocock, 1903 as the sister group to the New Zealand endemic family Synthetonychiidae Forster, 1954. With the exception of the Laurasian representatives of the family, all landmasses contain non-monophyletic assemblages of taxa. To determine whether this non-monophyly was the result of Gondwanan vicariance, ancient cladogenesis due to habitat regionalisation, or more recent over-water dispersal, we inferred divergence times. We found that most divergence times between landmasses predate Gondwanan breakup, though there has been at least one instance of transoceanic dispersal – to New Caledonia. In all, we identify multiple places in the phylogeny where taxonomic revision is needed, and transfer Lomanella outside of Triaenonychidae in order to maintain monophyly of the family.

Strangers in a strange land: Ecological dissimilarity to metatherian carnivores may partly explain early colonization of South America by Cyonasua-group procyonids

AbstractIt was once thought that the endemic carnivorous mammals of South America, the metatherian sparassodonts, were driven extinct by North American carnivorans through competitive exclusion. However, sparassodonts went extinct before most groups of carnivorans entered South America; only the endemic Cyonasua-group procyonids (Cyonasua and Chapalmalania), which immigrated to South America nearly 4 million years earlier than other carnivorans, significantly overlapped with sparassodonts in time. In this study, we examine the functional morphology of the dentition of Cyonasua and Chapalmalania through quantitative analysis to determine the dietary habits of these taxa and the degree to which they may have ecologically overlapped sparassodonts and large predatory Neogene didelphimorphians. We find Cyonasua and Chapalmalania to be more carnivorous than extant procyonids, other than Bassariscus, in agreement with previous studies, but more omnivorous than most other carnivorans and all meat-eating South American metatherians, including sparassodonts. The extreme ecological dissimilarity between Cyonasua-group procyonids and members of the endemic South American predator guild may explain why procyonids were able to successfully establish themselves in South America several million years earlier than most other northern mammals (including all other carnivorans): they moved into a previously unoccupied ecological niche (large omnivore) and avoided direct competition with incumbent native species, a situation similar to that documented in historical cases of biological invasion. The omnivorous diets and climbing/swimming abilities of procyonids may have increased their chances for a successful over-water dispersal relative to other carnivorans, further favoring their successful establishment in South America.

Somewhere beyond the sea: Human cranial remains from the Lesser Sunda Islands (Alor Island, Indonesia) provide insights on Late Pleistocene peopling of Island Southeast Asia

The migration of anatomically modern humans (AMH) from Africa to every inhabitable continent included their dispersal through Island Southeast Asia (ISEA) to Australia. Significantly, this involved overwater dispersal through the Lesser Sunda Islands between Sunda (continental Southeast Asia) and Sahul (Australia and New Guinea). However, the timing and direction of this movement is still debated. Here, we report on human skeletal material recovered from excavations at two rockshelters, known locally as Tron Bon Lei, on Alor Island, Indonesia. The remains, dated to the Late Pleistocene, are the first anatomically modern human remains recovered in Wallacea dated to this period and are associated with cultural material demonstrating intentional burial. The human remains from Tron Bon Lei represent a population osteometrically distinct from Late Pleistocene Sunda and Sahul AMH. Instead, morphometrically, they appear more similar to Holocene populations in the Lesser Sundas. Thus, they may represent the remains of a population originally from Sunda whose Lesser Sunda Island descendants survived into the Holocene.

Island Ancestors and New World Biogeography: A Case Study from the Scorpions (Buthidae: Centruroidinae)

Scorpions are an excellent system for understanding biogeographical patterns. Most major scorpion lineages predate modern landforms, making them suitable for testing hypotheses of vicariance and dispersal. The Caribbean islands are endowed with a rich and largely endemic scorpion fauna, the origins of which have not been previously investigated with modern biogeographical methods. Three sets of hypotheses have been proposed to explain present patterns of diversity in the Caribbean: (1) connections via land bridges, (2) vicariance events, and (3) overwater dispersal from continents and among islands. The present study investigates the biogeographical diversification of the New World buthid scorpion subfamily Centruroidinae Kraus, 1955, a clade of seven genera and more than 110 species; infers the ancestral distributions of these scorpions; and tests the relative roles of vicariance and dispersal in the formation of their present distributions. A fossil-calibrated molecular phylogeny was estimated with a Bayesian criterion to infer the dates of diversification events from which ancestral distributions were reconstructed, and the relative likelihood of models of vicariance vs. dispersal, calculated. Although both the timing of diversification and the ancestral distributions were congruent with the GAARlandia land-bridge hypothesis, there was no significant difference between distance-dependent models with or without the land-bridge. Heteroctenus Pocock, 1893, the Caribbean-endemic sister taxon of Centruroides Marx, 1890 provides evidence for a Caribbean ancestor, which subsequently colonized Central America and North America, and eventually re-colonized the Greater Antilles. This ‘reverse colonization’ event of a continent from an island demonstrates the importance of islands as a potential source of biodiversity.

Biogeography of the Caribbean Cyrtognatha spiders

Island systems provide excellent arenas to test evolutionary hypotheses pertaining to gene flow and diversification of dispersal-limited organisms. Here we focus on an orbweaver spider genus Cyrtognatha (Tetragnathidae) from the Caribbean, with the aims to reconstruct its evolutionary history, examine its biogeographic history in the archipelago, and to estimate the timing and route of Caribbean colonization. Specifically, we test if Cyrtognatha biogeographic history is consistent with an ancient vicariant scenario (the GAARlandia landbridge hypothesis) or overwater dispersal. We reconstructed a species level phylogeny based on one mitochondrial (COI) and one nuclear (28S) marker. We then used this topology to constrain a time-calibrated mtDNA phylogeny, for subsequent biogeographical analyses in BioGeoBEARS of over 100 originally sampled Cyrtognatha individuals, using models with and without a founder event parameter. Our results suggest a radiation of Caribbean Cyrtognatha, containing 11 to 14 species that are exclusively single island endemics. Although biogeographic reconstructions cannot refute a vicariant origin of the Caribbean clade, possibly an artifact of sparse outgroup availability, they indicate timing of colonization that is much too recent for GAARlandia to have played a role. Instead, an overwater colonization to the Caribbean in mid-Miocene better explains the data. From Hispaniola, Cyrtognatha subsequently dispersed to, and diversified on, the other islands of the Greater, and Lesser Antilles. Within the constraints of our island system and data, a model that omits the founder event parameter from biogeographic analysis is less suitable than the equivalent model with a founder event.

Huntsmen of the Caribbean: Multiple tests of the GAARlandia hypothesis

The origin of the Caribbean biota remains debated, but amassing evidence suggests important roles of both dispersal and vicariance events in the colonization the archipelago. The most prominent vicariance hypothesis is colonization over the GAARlandia land bridge that putatively connected the Greater Antilles to South America around 33 mya. This hypothesis has received support from studies of individual lineages, but its main prediction—the simultaneous colonization of multiple lineages during that time window—requires further unambiguous corroboration. Here, we examine the phylogenetic structure of huntsman spiders (Sparassidae) of the Caribbean. Huntsman spiders are appropriate models for this question, as they are expected to be dispersal limited as substrate and foliage dwelling spiders that rarely balloon, yet are found on some volcanic islands, and thus at least some overwater dispersal must have occurred. We focus on the Caribbean endemic Neostasina, but also include Caribbean Olios, for a deeper biogeographical understanding. We use two mitochondrial and four nuclear markers to reconstruct dated phylogenetic trees and to test taxonomic and biogeographic hypotheses. Our analyses strongly support the monophyly of Neostasina and the polyphyly of Olios, with a new clade endemic to the Caribbean. Both Neostasina and Caribbean Olios occur on the Greater and Lesser Antilles and independently colonized the Caribbean around 36–28 mya. Hypothesis testing in BioGeoBEARS suggests a role of the GAARlandia landbridge in the colonization of both clades. The ‘Olios-like’ clade, in contrast, is restricted to the southern Lesser Antilles and shows a biogeographic history consistent with colonization from S. America, probably within the last 10 my. Thus, many spider lineages on the Greater Antilles seem to have colonized the Caribbean during a relatively short time span approximately coinciding with the proposed timing of GAARlandia. The synchronous colonization of multiple lineages suggests a temporary land connection. However, the main problem in concluding synchronous events across lineages in this study, as in most others, is the ambiguity in chronogram analyses meaning that many different patterns can be ‘consistent’ with GAARlandia, thus potentially providing a false positive result. Broad comparative biogeographical studies such as the CarBio project will offer the best opportunity to multiply test shared biogeographic patterns among independent lineages. The current paper contributes evidence from multiple lineages that will contribute to this synthesis.

From Gondwana to GAARlandia: Evolutionary history and biogeography of ogre‐faced spiders (Deinopis)

AbstractAimWe explore the evolutionary history of the ogre‐faced spiders (Deinopis) from their Early Cretaceous origins to present day. Specifically, we investigate how vicariance and dispersal have shaped distribution patterns of this lineage. Within the Caribbean, we test the role of GAARlandia, a hypothesized land bridge that connected South America to the Greater Antilles during the Eocene–Oligocene transition (~35–33 Ma), in the biogeography of Deinopis.TaxonAraneae: Deinopidae: Deinopis.LocationCaribbean islands, with additional global exemplars.MethodsCombining standard Sanger sequence data with an Anchored Hybrid Enrichment (AHE) phylogenomic dataset, we use Bayesian inference to estimate the phylogenetic relationships of Deinopis. “BioGeoBEARS” is used to test the GAARlandia hypothesis, and to pinpoint major dispersal events in the biogeographic history of Deinopis.ResultsThe phylogeny supports the nesting of a Caribbean clade within a continental grade. Model comparisons indicate GAARlandia as the best fitting model, and the biogeographic analyses reflect the geologic history within the Caribbean. Ancient and recent overwater dispersal events are also indicated within this lineage. There is also an ancient 113 Ma split into Old and New World clades.Main ConclusionsThe Deinopis phylogeny corresponds well with geography. This is reflected in the support for the GAARlandia land bridge hypothesis and the phylogenetic relationships within and among Caribbean islands mirroring nuances of Caribbean geologic history. Overwater dispersal also plays an important role in the biogeographic history of this lineage as implicated in the colonization of the volcanic and sedimentary Lesser Antilles and in a “reverse” colonization of North America. The spider family Deinopidae is an ancient lineage with origins dating back to Gondwana. While overwater dispersal has clearly played a role in the biogeography of the genus, the Deinopis phylogeny bears a strong signature of ancient geological events.

Diversification of Petroica robins across the Australo-Pacific region: first insights into the phylogenetic affinities of New Guinea’s highland robin species

ABSTRACT Complex spatial and temporal phylogenetic patterns have emerged among Pacific Island radiations and their Australian and New Guinean congeners. We explore the diversification of Australo-Pacific Petroica robins using the first phylogeny with complete species-level sampling of the genus. In doing so we provide the first assessment of the phylogenetic affinities of two poorly known species with highly restricted ranges in the highlands of New Guinea – Subalpine Robin (Petroica bivittata) and Snow Mountain Robin (P. archboldi). Our analyses suggest that Petroica underwent an initial diversification during the Plio-Pleistocene that established four major lineages restricted to New Zealand (four species), Australia (four species), New Guinea (two species) and Pacific Islands + Australia (three or four species). All lineages appear to have undergone species diversification in situ with the exception of the Pacific Islands + Australia lineage where long-distance over-water dispersal must be invoked to explain the placement of the Red-capped Robin (P. goodenovii) within the iconic Pacific robin species complex (P. multicolor + pusilla). Two scenarios fit this biogeographic pattern: (1) a single ‘upstream’ colonisation of mainland Australia from a Pacific Island ancestor resulting in P. goodenovii, or (2) two or three ‘downstream’ colonisations from a mainland Australian or New Guinean ancestor resulting in the distinct Pacific robin lineages that occur in the south-west Pacific. Overall, biogeographic patterns in Petroica suggest that long-distance dispersal and island colonisations have been rare events in this group, which contrasts with other Australo-Pacific radiations that show evidence for repeated long-distance dispersals and multiple instances of secondary sympatry on islands across the Pacific.

Sky, sea, and forest islands: Diversification in the African leaf‐folding frog Afrixalus paradorsalis (Anura: Hyperoliidae) of the Lower Guineo‐Congolian rain forest

AbstractAimTo investigate how putative barriers, forest refugia, and ecological gradients across the lower Guineo‐Congolian rain forest shape genetic and phenotypic divergence in the leaf‐folding frog Afrixalus paradorsalis, and examine the role of adjacent land bridge and sky‐islands in diversification.LocationThe Lower Guineo‐Congolian Forest, the Cameroonian Volcanic Line (CVL), and Bioko Island, Central Africa.TaxonAfrixalus paradorsalis (Family: Hyperoliidae), an African leaf‐folding frog.MethodsWe used molecular and phenotypic data to investigate diversity and divergence among the A. paradorsalis species complex distributed across lowland rain forests, a land bridge island, and mountains in Central Africa. We examined the coincidence of population boundaries, landscape features, divergence times, and spatial patterns of connectivity and diversity, and subsequently performed demographic modelling using genome‐wide SNP variation to distinguish among divergence mechanisms in mainland (riverine barriers, forest refugia, ecological gradients) and land bridge island populations (vicariance, overwater dispersal).ResultsWe detected four genetically distinct allopatric populations corresponding to Bioko Island, the CVL, and two lowland rain forest populations split by the Sanaga River. Although lowland populations are phenotypically indistinguishable, pronounced body size evolution occurs at high elevation, and the timing of the formation of the high elevation population coincides with mountain uplift in the CVL. Spatial analyses and demographic modelling revealed population divergence across mainland Lower Guinea is best explained by forest refugia rather than riverine barriers or ecological gradients, and that the Bioko Island population divergence is best explained by vicariance (marine incursion) rather than overseas dispersal.Main conclusionsWe provide growing support for the important role of forest refugia in driving intraspecific divergences in the Guineo‐Congolian rain forest. In A. paradorsalis, sky‐islands in the CVL have resulted in greater genetic and phenotypic divergences than marine incursions of the land bridge Bioko Island, highlighting important differences in patterns of island‐driven diversification in Lower Guinea.

Appropriate fossil calibrations and tree constraints uphold the Mesozoic divergence of solenodons from other extant mammals

The mammalian order Eulipotyphla includes four extant families of insectivorans: Solenodontidae (solenodons); Talpidae (moles); Soricidae (shrews); and Erinaceidae (hedgehogs). Of these, Solenodontidae includes only two extant species, which are endemic to the largest islands of the Greater Antilles: Cuba and Hispaniola. Most molecular studies suggest that eulipotyphlan families diverged from each other across several million years, with the basal split between Solenodontidae and other families occurring in the Late Cretaceous. By contrast, Sato et al. (2016) suggest that eulipotyphlan families diverged from each other in a polytomy ∼58.6 million years ago (Mya). This more recent divergence estimate for Solenodontidae versus other extant eulipotyphlans suggests that solenodons must have arrived in the Greater Antilles via overwater dispersal rather than vicariance. Here, we show that the young timetree estimates for eulipotyphlan families and the polytomy are due to an inverted ingroup-outgroup arrangement of the tree, the result of using Tracer rather than TreeAnnotator to compile interfamilial divergence times, and of not enforcing the monophly of well-established clades such as Laurasiatheria and Eulipotyphla. Finally, Sato et al.’s (2016) timetree includes several zombie lineages where estimated divergence times are much younger than minimum ages that are implied by the fossil record. We reanalyzed Sato et al.’s (2016) original data with enforced monophyly for well-established clades and updated fossil calibrations that eliminate the inference of zombie lineages. Our resulting timetrees, which were compiled with TreeAnnotator rather than Tracer, produce dates that are in good agreement with other recent studies and place the basal split between Solenodontidae and other eulipotyphlans in the Late Cretaceous.

Multiple origins of the Phaenonotum beetles in the Greater Antilles (Coleoptera: Hydrophilidae): phylogeny, biogeography and systematics

The systematics and the phylogenetic position of the Caribbean representatives of Phaenonotum Sharp (Coleoptera: Hydrophilidae) are investigated in order to understand the composition of the Caribbean fauna and its origin. Phylogenetic analysis based on mitochondrial and nuclear genes has revealed the Caribbean species to be situated in three deeply nested clades, inferring multiple colonization of Caribbean islands from the continent. Time-tree analysis and BioGeoBEARS analyses of ancestral ranges estimated the oldest clade, consisting of wingless single-island endemics of Cuba ( P. delgadoi ), Jamaica ( P. ondreji sp. nov. ) and Hispaniola ( P. laterale sp. nov. ), to have diverged ca. 46.6 Ma from the South American ancestor and subsequently colonizing the Caribbean most likely via the GAARlandia land bridge connecting South America with Greater Antilles. The remaining three Caribbean species, including the Puerto Rican endemic, P. borinquenum sp. nov. , are of more recent (Miocene to Pliocene) origin and colonized the Greater Antilles by over-water dispersal. All the Caribbean species are illustrated and diagnosed and three new species are described. The genus Phaenonotum , excluding P. caribense Archangelsky, is confirmed as a monophylum. We demonstrate that species-level taxonomy of Phaenonotum is difficult to solve by morphology alone, and ideally requires the combination of morphology and molecular markers.

An incipient invasion of brown anole lizards (Anolis sagrei) into their own native range in the Cayman Islands: a case of cryptic back-introduction

Human-mediated dispersal has reshaped distribution patterns and biogeographic relationships for many taxa. Long-distance and over-water dispersal were historically rare events for most species, but now human activities can move organisms quickly over long distances to new places. A potential consequence of human-mediated dispersal is the eventual reintroduction of individuals from an invasive population back into their native range; a dimension of biological invasion termed “cryptic back-introduction.” We investigated whether this phenomenon was occurring in the Cayman Islands where brown anole lizards (Anolis sagrei) with red dewlaps (i.e., throat fans), either native to Little Cayman or invasive on Grand Cayman, have been found on Cayman Brac where the native A. sagrei have yellow dewlaps. Our analysis of microsatellite data shows strong population-genetic structure among the three Cayman Islands, but also evidence for non-equilibrium. We found some instances of intermediate multilocus genotypes (possibly 3–9% of individuals), particularly between Grand Cayman and Cayman Brac. Furthermore, analysis of dewlap reflectance data classified six males sampled on Cayman Brac as having red dewlaps similar to lizards from Grand Cayman and Little Cayman. Lastly, one individual from Cayman Brac had an intermediate microsatellite genotype, a red dewlap, and a mtDNA haplotype from Grand Cayman. This mismatch among genetic and phenotypic data strongly suggests that invasive A. sagrei from Grand Cayman are interbreeding with native A. sagrei on Cayman Brac. To our knowledge, this is the first evidence of cryptic back-introduction. Although we demonstrate this phenomenon is occurring in the Cayman Islands, assessing its frequency there and prevalence in other systems may prove difficult due to the need for genetic data in most instances. Cryptic back-introductions may eventually provide some insight into how lineages are changed by the invasion process and may be an underappreciated way in which invasive species impact native biodiversity.

Molecular phylogenetic analysis of nuclear genes suggests a Cenozoic over-water dispersal origin for the Cuban solenodon.

The Cuban solenodon (Solenodon cubanus) is one of the most enigmatic mammals and is an extremely rare species with a distribution limited to a small part of the island of Cuba. Despite its rarity, in 2012 seven individuals of S. cubanus were captured and sampled successfully for DNA analysis, providing new insights into the evolutionary origin of this species and into the origins of the Caribbean fauna, which remain controversial. We conducted molecular phylogenetic analyses of five nuclear genes (Apob, Atp7a, Bdnf, Brca1 and Rag1; total, 4,602 bp) from 35 species of the mammalian order Eulipotyphla. Based on Bayesian relaxed molecular clock analyses, the family Solenodontidae diverged from other eulipotyphlan in the Paleocene, after the bolide impact on the Yucatan Peninsula, and S. cubanus diverged from the Hispaniolan solenodon (S. paradoxus) in the Early Pliocene. The strikingly recent divergence time estimates suggest that S. cubanus and its ancestral lineage originated via over-water dispersal rather than vicariance events, as had previously been hypothesised.

Influences of climate and historical land connectivity on ant beta diversity in East Asia

AbstractAimBiodiversity patterns reflect both ecological and evolutionary processes interacting with geographical variation in climate and the current and historical connectivity between land areas. We sought to disentangle these effects in explaining the organization of ant diversity across geographical areas and islands in East Asia.LocationThe Japanese Archipelago including the Ryukyu and Ogasawara Islands, Taiwan and coastal continental regions of Korea, China and Russia.MethodsWe aggregated species occurrence records from published literature, specimen databases and museum records, and compiled climatic variables for islands and politically defined continental areas. Current and historical land connections in the Last Glacial Maximum were determined using bathymetric databases. We analysed factors driving patterns of Simpson composition dissimilarity using multiple regression of distance matrices.ResultsTemperature was the largest driver of dissimilarity among areas, with geographical distance and historical land contiguity also being important. Current land contiguity had no detectable effect.Main conclusionsWe found climate to be a primary driver of ant diversity patterns on large scales, consistent with previous work on ants and other organisms. Interestingly, land connectivity during historical periods of low sea level was more important than current land connectivity in explaining faunal similarities. This implies that despite the potential overwater dispersal of ants, overland dispersal via transient land connections is a more important driver of regional‐scale biogeographical pattern in East Asia.

Body-size trends inPeromyscus(Rodentia: Cricetidae) on Vancouver Island, Canada, with comments on relictual gigantism

AbstractLarge body size in Keen’s mouse,Peromyscus keeni, has been regarded as a relictual character that developed in times of geographic separation fromP. maniculatus. However, body-size changes in Keen’s mouse have not been studied in detail. To address this problem the present paper compares the size of ancient and modernPeromyscusspecimens from Vancouver Island. Results indicate that Late PleistocenePeromyscusfrom Arch-2 Cave and early HolocenePeromyscusfrom Pellucidar Cave are significantly larger than those of modernP. maniculatusandP. keeni. Morphology and linear discriminant analyses support tentative assignment of several ancient specimens toP. keeni. Radiocarbon age estimates of 11,960±45 BP (14,004–13,637 cal BP) on a small mammal bone and 12,370±35 BP (14,695–14,148 cal BP) onUrsus arctosfrom Arch-2 Cave place these faunas on the island as relative sea level fell from a postglacial highstand, suggesting a local source for faunas with limited over-water dispersal capacities. Results of this study are consistent with insular relictual gigantism in Keen’s mouse, although some modification of the original hypothesis is needed to explain the smaller size of modern than ancient mice.

First North American fossil monkey and early Miocene tropical biotic interchange.

New World monkeys (platyrrhines) are a diverse part of modern tropical ecosystems in North and South America, yet their early evolutionary history in the tropics is largely unknown. Molecular divergence estimates suggest that primates arrived in tropical Central America, the southern-most extent of the North American landmass, with several dispersals from South America starting with the emergence of the Isthmus of Panama 3-4 million years ago (Ma). The complete absence of primate fossils from Central America has, however, limited our understanding of their history in the New World. Here we present the first description of a fossil monkey recovered from the North American landmass, the oldest known crown platyrrhine, from a precisely dated 20.9-Ma layer in the Las Cascadas Formation in the Panama Canal Basin, Panama. This discovery suggests that family-level diversification of extant New World monkeys occurred in the tropics, with new divergence estimates for Cebidae between 22 and 25 Ma, and provides the oldest fossil evidence for mammalian interchange between South and North America. The timing is consistent with recent tectonic reconstructions of a relatively narrow Central American Seaway in the early Miocene epoch, coincident with over-water dispersals inferred for many other groups of animals and plants. Discovery of an early Miocene primate in Panama provides evidence for a circum-Caribbean tropical distribution of New World monkeys by this time, with ocean barriers not wholly restricting their northward movements, requiring a complex set of ecological factors to explain their absence in well-sampled similarly aged localities at higher latitudes of North America.

Spintharus flavidusin the Caribbean—a 30 million year biogeographical history and radiation of a ‘widespread species’

The Caribbean island biota is characterized by high levels of endemism, the result of an interplay between colonization opportunities on islands and effective oceanic barriers among them. A relatively small percentage of the biota is represented by ‘widespread species,’ presumably taxa for which oceanic barriers are ineffective. Few studies have explored in detail the genetic structure of widespread Caribbean taxa. The cobweb spider Spintharus flavidus Hentz, 1850 (Theridiidae) is one of two described Spintharus species and is unique in being widely distributed from northern N. America to Brazil and throughout the Caribbean. As a taxonomic hypothesis, Spintharus “flavidus” predicts maintenance of gene flow among Caribbean islands, a prediction that seems contradicted by known S. flavidus biology, which suggests limited dispersal ability. As part of an extensive survey of Caribbean arachnids (project CarBio), we conducted the first molecular phylogenetic analysis of S. flavidus with the primary goal of testing the ‘widespread species’ hypothesis. Our results, while limited to three molecular loci, reject the hypothesis of a single widespread species. Instead this lineage seems to represent a radiation with at least 16 species in the Caribbean region. Nearly all are short range endemics with several distinct mainland groups and others are single island endemics. While limited taxon sampling, with a single specimen from S. America, constrains what we can infer about the biogeographical history of the lineage, clear patterns still emerge. Consistent with limited overwater dispersal, we find evidence for a single colonization of the Caribbean about 30 million years ago, coinciding with the timing of the GAARLandia landbridge hypothesis. In sum, S. “flavidus” is not a single species capable of frequent overwater dispersal, but rather a 30 my old radiation of single island endemics that provides preliminary support for a complex and contested geological hypothesis.

Phylogeny of the island archipelago frog genus Sanguirana: Another endemic Philippine radiation that diversified 'Out-of-Palawan'.

Recent higher-level frog phylogenetic analyses have included a few members of the endemic Philippine frog genus Sanguirana. Although the monophyly of the group has never been disputed, the recent phylogenetically-supported inclusion of the Palawan Wood Frog (Sanguirana sanguinea) in this clade was highly unexpected. In addition, species boundaries and relationships remain unclear and new species continue to be discovered. We estimate the phylogeny for this endemic Philippine genus using two mitochondrial gene regions and six nuclear loci and complete sampling for all known species. We use a time-calibrated Bayesian estimate of phylogeny and model-testing approach to biogeographic inference to infer ancestral areas and probable means of diversification. These analyses identify Sanguirana as an additional clade for which the 'Out-of-Palawan' biogeographic scenario is unambiguously preferred. This study lends additional support to recent work suggesting that a substantial portion of Philippine vertebrate megadiversity originated via colonization of the archipelago from the Palawan microcontinent, with subsequent invasion of oceanic islands (e.g., range expansion over Huxley's Modification of Wallace's Line), numerous instances of overwater dispersal, and geographic radiation across the archipelago.

Historical biogeography resolves the origins of endemic Arabian toad lineages (Anura: Bufonidae): Evidence for ancient vicariance and dispersal events with the Horn of Africa and South Asia.

BackgroundThe Arabian Peninsula is home to a unique fauna that has assembled and evolved throughout the course of major geophysical events, including the separation of the Arabian Plate from Africa and subsequent collision with Eurasia. Opportunities for faunal exchanges with particular continents occurred in temporally distinct periods, and the presence of African, Western Eurasian, and South Asian derived taxa on the Arabian Peninsula signifies the complexity of these historical biogeographic events. The six true toad species (family Bufonidae) endemic to the Arabian Peninsula present a considerable taxonomic and biogeographic challenge because they are part of a global bufonid radiation, including several genera surrounding the Arabian Peninsula, and difficult to discriminate morphologically. As they could be derived from African, Western Eurasian, or South Asian toad groups, elucidating their evolutionary relationships has important implications for historical biogeography. Here, we analyze a global molecular data set of 243 bufonid lineages, with an emphasis on new sampling from the Horn of Africa, Western Eurasia, South Asia, and the Arabian Peninsula, to reconstruct the evolutionary relationships of the Arabian species. We produce a robust time-calibrated phylogeny to infer the biogeographic history of this group on and around the Arabian Peninsula.ResultsOur phylogenetic analyses indicate two of the endemic Arabian toad species, “Bufo” tihamicus and “Bufo” arabicus, evolved independently within the African genus Amietophrynus. We confirm the Arabian species Duttaphrynus dhufarensis is of South Asian origin, but do not find evidence for the Asian genus Duttaphrynus being present in the Horn of Africa, discrediting a previously proposed Asian bufonid dispersal event to Africa. We also do not find evidence of the African genus Amietophrynus occurring in South Asia, suggesting that unlike many other vertebrate taxa, toads have not used the Arabian Peninsula as a stepping-stone for trans-continental dispersal. Our divergence dating estimates strongly suggest the formation of the Red Sea drove simultaneous divergences between two of the Arabian species (A. tihamicus comb. nov. and A. arabicus comb. nov.) and their closest mainland African relatives in the Early Miocene. We estimate the divergence of D. dhufarensis with its closest South Asian relatives occurred in the mid to Late Miocene, suggesting the temporary or permanent land connections between the Arabian plate and Eurasia facilitated dispersal of this lineage to the Arabian Peninsula.ConclusionsThe Arabian bufonid assemblage, despite being comparatively depauperate with respect to surrounding continents, exemplifies the faunal pattern of the Arabian Peninsula, namely being a complex admixture of African, Western Eurasian, and South Asian elements. The historical biogeographic patterns exhibited by Arabian toads and their allies are concordant with studies of other vertebrate taxa, building support for the role of major geological events in driving simultaneous vicariance and dispersal events around the Arabian Peninsula. Although many taxa or groups exhibiting disjunct Afro-Arabian distributions appear to have dispersed more recently from the Horn of Africa via a southern land bridge or overwater dispersal, both Amietophrynus tihamicus and A. arabicus likely represent true African relicts resulting from vicariance associated with the Red Sea formation, a pattern that so far is rare among the vertebrate species investigated.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0417-y) contains supplementary material, which is available to authorized users.

Xenopus in Space and Time: Fossils, Node Calibrations, Tip-Dating, and Paleobiogeography

Published data from DNA sequences, morphology of 11 extant and 15 extinct frog taxa, and stratigraphic ranges of fossils were integrated to open a window into the deep-time evolution of Xenopus. The ages and morphological characters of fossils were used as independent datasets to calibrate a chronogram. We found that DNA sequences, either alone or in combination with morphological data and fossils, tended to support a close relationship between Xenopus and Hymenochirus, although in some analyses this topology was not significantly better than the Pipa + Hymenochirus topology. Analyses that excluded DNA data found strong support for the Pipa + Hymenochirus tree. The criterion for selecting the maximum age of the calibration prior influenced the age estimates, and our age estimates of early divergences in the tree of frogs are substantially younger than those of published studies. Node-dating and tip-dating calibrations, either alone or in combination, yielded older dates for nodes than did a root calibration alone. Our estimates of divergence times indicate that overwater dispersal, rather than vicariance due to the splitting of Africa and South America, may explain the presence of Xenopus in Africa and its closest fossil relatives in South America.