Across the Indian Ocean: A remarkable example of trans-oceanic dispersal in an austral mygalomorph spider

Single-Island Endemism despite Repeated Dispersal in Caribbean Micrathena (Araneae: Araneidae): An Updated Phylogeographic Analysis

Island biogeographers have long sought to elucidate the mechanisms behind biodiversity genesis. The Caribbean presents a unique stage on which to analyze the diversification process, due to the geologic diversity among the islands and the rich biotic diversity with high levels of island endemism. The colonization of such islands may reflect geologic heterogeneity through vicariant processes and/ or involve long-distance overwater dispersal. Here, we explore the phylogeography of the Caribbean and proximal mainland spiny orbweavers (Micrathena, Araneae), an American spider lineage that is the most diverse in the tropics and is found throughout the Caribbean. We specifically test whether the vicariant colonization via the contested GAARlandia landbridge (putatively emergent 33–35 mya), long-distance dispersal (LDD), or both processes best explain the modern Micrathena distribution. We reconstruct the phylogeny and test biogeographic hypotheses using a ‘target gene approach’ with three molecular markers (CO1, ITS-2, and 16S rRNA). Phylogenetic analyses support the monophyly of the genus but reject the monophyly of Caribbean Micrathena. Biogeographical analyses support five independent colonizations of the region via multiple overwater dispersal events, primarily from North/Central America, although the genus is South American in origin. There is no evidence for dispersal to the Greater Antilles during the timespan of GAARlandia. Our phylogeny implies greater species richness in the Caribbean than previously known, with two putative species of M. forcipata that are each single-island endemics, as well as deep divergences between the Mexican and Floridian M. sagittata. Micrathena is an unusual lineage among arachnids, having colonized the Caribbean multiple times via overwater dispersal after the submergence of GAARlandia. On the other hand, single-island endemism and undiscovered diversity are nearly universal among all but the most dispersal-prone arachnid groups in the Caribbean.

Repeated colonization, adaptive radiation and convergent evolution in the sheet-weaving spiders (Linyphiidae) of the south Pacific Archipelago of Juan Fernandez

We report on the colonization and diversification of linyphiid spiders in the Pacific oceanic archipelago of Juan Fernandez. About 50 spider species occur naturally in these islands, most of them endemic and about half of them are linyphiids. Linyphiidae includes no fewer than 15 species of Laminacauda and three of Neomaso (with several additional undescribed species in the latter genus), all of them single island endemics. There are three additional linyphiid endemic genera, two monotypic and one, Juanfernandezia, with two species. Unlike the rather uniform somatic morphology and small ground sheet webs of the continental Laminacauda and Neomaso species, the Juan Fernandez endemics exhibit morphological features and life history traits that are very rare or unknown in any other linyphiids. A multi-locus phylogenetic analysis confirms at least five independent Juan Fernandez colonizations of Linyphiidae, two within the same genus, and three of which underwent subsequent local diversification. Different calibrations suggest alternative colonization timelines, some at odds with island ages, but all agree on similar diversification timings of the endemic lineages. Rare phenotypic traits (e.g. gigantism, massive chelicerae or elongated legs) evolved multiple times independently within the islands. Based on the remarkable levels of eco-phenotypic differentiation in locally diversified species showing densely packed distributions, we propose that Laminacauda, and probably Neomaso, constitute a case of adaptive radiation.

Descriptions of four new trapdoor spider species in the subfamily Ummidiinae from Thailand (Araneae, Mygalomorphae, Halonoproctidae)

Males and females of four mygalomorph spider species (family Halonoproctidae, subfamily Ummidiinae) are newly described from Thailand, and the taxonomy of Ummidiinae is discussed. This is the first time that trapdoor spider species in this subfamily are described from Thailand. Two of these new species belong to the genus Conothele, the other two species are placed in the genus Latouchia. Conothele martensi spec. nov. was found in the north of the country (Chiang Mai Province), C. isan spec. nov. and Latouchia incerta spec. nov. were collected in northeastern Thailand (Buri Ram Province, Surin Province and Roi Et Province), and L. maculosa spec. nov. was found in the southern coastal province of Prachuap Khiri Khan.

Volcanism and palaeoclimate change drive diversification of the world's largest whip spider (Amblypygi)

The tropics contain many of the most biodiverse regions on Earth but the processes responsible for generating this diversity remain poorly understood. This study investigated the drivers of diversification in arthropods with stenotopic ecological requirements and limited dispersal capability using as a model the monotypic whip spider (Amblypygi) genus Acanthophrynus, widespread in the tropical deciduous forests of Mexico. We hypothesized that for these organisms, the tropical deciduous forests serve as a conduit for dispersal, with their disappearance imposing barriers. Given that these forests are located in a region of complex geological history and that they fluctuated in extent during the Pliocene-Pleistocene glacial/interglacial cycles we combine molecular divergence dating, palaeoclimatic niche modelling and ancestral area reconstruction to test if and when habitat fragmentation promoted diversification in Acanthophrynus. Concomitant with the expected role of landscape change, we demonstrate that orogeny of the Trans-Mexican Volcanic Belt, in the Late Miocene or Early Pliocene (6.95-5.21 million years ago), drove the earliest divergence of Acanthophrynus by vicariance. Similarly, as expected, the later onset of glaciations strongly impacted diversification. Whereas a more stable climate in the southern part of the distribution enabled further diversification, a marked loss of suitable habitat during the glaciations only allowed dispersal and diversification in the north to occur later, resulting in a lower overall diversity in this region. Barriers and diversification patterns identified in Acanthophrynus are reflected in the phylogeography of codistributed vertebrates and arthropods, emphasizing the profound impact of Trans-Mexican Volcanic Belt orogeny and glacial/interglacial cycles as drivers of diversification in the Mexican Neotropics.

Diversification of the mygalomorph spider genus Aname (Araneae: Anamidae) across the Australian arid zone: Tracing the evolution and biogeography of a continent-wide radiation

The assembly of the Australian arid zone biota has long fascinated biogeographers. Covering over two-thirds of the continent, Australia's vast arid zone biome is home to a distinctive fauna and flora, including numerous lineages which have diversified since the Eocene. Tracing the origins and speciation history of these arid zone taxa has been an ongoing endeavour since the advent of molecular phylogenetics, and an increasing number of studies on invertebrate animals are beginning to complement a rich history of research on vertebrate and plant taxa. In this study, we apply continent-wide genetic sampling and one of the largest phylogenetic data matrices yet assembled for a genus of Australian spiders, to reconstruct the phylogeny and biogeographic history of the open-holed trapdoor spider genus Aname L. Koch, 1873. This highly diverse lineage of Australian mygalomorph spiders has a distribution covering the majority of Australia west of the Great Dividing Range, but apparently excluding the high rainfall zones of eastern Australia and Tasmania. Original and legacy sequences were obtained for three mtDNA and four nuDNA markers from 174 taxa in seven genera, including 150 Aname specimen terminals belonging to 102 species-level operational taxonomic units, sampled from 32 bioregions across Australia. Reconstruction of the phylogeny and biogeographic history of Aname revealed three radiations (Tropical, Temperate-Eastern and Continental), which could be further broken into eight major inclusive clades. Ancestral area reconstruction revealed the Pilbara, Monsoon Tropics and Mid-West to be important ancestral areas for the genus Aname and its closest relatives, with the origin of Aname itself inferred in the Pilbara bioregion. From these origins in the arid north-west of Australia, our study found evidence for a series of subsequent biome transitions in separate lineages, with at least eight tertiary incursions back into the arid zone from more mesic tropical, temperate or eastern biomes, and only two major clades which experienced widespread (primary) in situ diversification within the arid zone. Based on our phylogenetic results, and results from independent legacy divergence dating studies, we further reveal the importance of climate-driven biotic change in the Miocene and Pliocene in shaping the distribution and composition of the Australian arid zone biota, and the value of continent-wide studies in revealing potentially complex patterns of arid zone diversification in dispersal-limited invertebrate taxa.

Trapped indoors? Long-distance dispersal in mygalomorph spiders and its effect on species ranges

The Mygalomorphae includes tarantulas, trapdoor, funnel-web, purse-web and sheet-web spiders, species known for poor dispersal abilities. Here, we attempted to compile all the information available on their long-distance dispersal mechanisms from observations that are often spread throughout the taxonomic literature. Mygalomorphs can disperse terrestrially, and in some tarantulas, for example, spiderlings walk together in single files away from their maternal burrow, a mechanism limited in distance covered. Conversely, at least eight species disperse aerially, via dropping on drag lines from elevated positions and being passively blown off ('suspended ballooning'). The first record of this behaviour is 135 years old, but we still know very little about it. Phylogeographic studies suggest several occurrences of transcontinental dispersal in the evolutionary history of mygalomorphs, but these might result from contingent rafting events, rather than regular dispersal mechanisms. We use occurrence data to show that suspended ballooning increases the species ranges in Australian mygalomorph families where this behaviour has been recorded. We also identified Anamidae, Idiopidae, and especially Atracidae, as families that might employ suspended ballooning or another efficient but undiscovered dispersal mechanism. Finally, we suggest that molecular studies with mitochondrial genes will help disentangle behavioural limitations of dispersal from ecological or physical ones.

Phylogenetic Systematics and Evolution of the Spider Infraorder Mygalomorphae Using Genomic Scale Data

The infraorder Mygalomorphae is one of the three main lineages of spiders comprising over 3000 nominal species. This ancient group has a worldwide distribution that includes among its ranks large and charismatic taxa such as tarantulas, trapdoor spiders, and highly venomous funnel-web spiders. Based on past molecular studies using Sanger-sequencing approaches, numerous mygalomorph families (e.g., Hexathelidae, Ctenizidae, Cyrtaucheniidae, Dipluridae, and Nemesiidae) have been identified as non-monophyletic. However, these data were unable to sufficiently resolve the higher-level (intra- and interfamilial) relationships such that the necessary changes in classification could be made with confidence. Here, we present a comprehensive phylogenomic treatment of the spider infraorder Mygalomorphae. We employ 472 loci obtained through anchored hybrid enrichment to reconstruct relationships among all the mygalomorph spider families and estimate the timeframe of their diversification. We sampled nearly all currently recognized families, which has allowed us to assess their status, and as a result, propose a new classification scheme. Our generic-level sampling has also provided an evolutionary framework for revisiting questions regarding silk use in mygalomorph spiders. The first such analysis for the group within a strict phylogenetic framework shows that a sheet web is likely the plesiomorphic condition for mygalomorphs, as well as providing insights to the ancestral foraging behavior for all spiders. Our divergence time estimates, concomitant with detailed biogeographic analysis, suggest that both ancient continental-level vicariance and more recent dispersal events have played an important role in shaping modern day distributional patterns. Based on our results, we relimit the generic composition of the Ctenizidae, Cyrtaucheniidae, Dipluridae, and Nemesiidae. We also elevate five subfamilies to family rank: Anamidae (NEW RANK), Euagridae (NEW RANK), Ischnothelidae (NEW RANK), Pycnothelidae (NEW RANK), and Bemmeridae (NEW RANK). Three families Entypesidae (NEW FAMILY), Microhexuridae (NEW FAMILY), and Stasimopidae (NEW FAMILY), and one subfamily Australothelinae (NEW SUBFAMILY) are newly proposed. Such a major rearrangement in classification, recognizing nine newly established family-level rank taxa, is the largest the group has seen in over three decades. [Biogeography; molecular clocks; phylogenomics; spider web foraging; taxonomy.].

Phylogeography of the ‘cosmopolitan’ orb-weaver Argiope trifasciata (Araneae: Araneidae)

Few spider species show truly cosmopolitan distributions. Among them is the banded garden spider Argiope trifasciata, which is reported from six continents across major climatic gradients and geographical boundaries. In orb-weaver spiders, such global distributions might be a result of lively dispersal via ballooning. However, wide distributions might also be artefactual, owing to our limited understanding of species taxonomy. To test the hypothesis that A. trifasciata might be a complex of cryptic species with more limited geographical ranges, we investigated the biogeographical structure and evolutionary history of A. trifasciata through a combination of time-calibrated phylogenetic analyses (57 terminals and three genes), ancestral range reconstruction and species delimitation methods. Our results strongly suggest that A. trifasciata as currently defined is not a single species. Its populations fall into five reciprocally monophyletic clades that are genetically distinct and have evolutionary origins in the Plio-Pleistocene. These clades are confined to East Asia, temperate Australia, Hawaii, the New World and the Old World (Africa and most of the Palaearctic). Our results provide the basis for future investigation of morphological and/or ecological disparity between the populations that are likely to represent species, in addition to examinations of the attributes and dispersal modes of these species.

Exploring the Interplay Between Local and Regional Drivers of Distribution of a Subterranean Organism

Caves are excellent model systems to study the effects of abiotic factors on species distributions due to their selective conditions. Different ecological factors have been shown to affect species distribution depending on the scale of analysis, whether regional or local. The interplay between local and regional factors in explaining the spatial distribution of cave-dwelling organisms is poorly understood. Using the troglophilic subterranean spider Artema nephilit (Araneae: Pholcidae) as a model organism, we investigated whether similar environmental predictors drive the species distribution at these two spatial scales. At the local scale, we monitored the abundance of the spiders and measured relevant environmental features in 33 caves along the Jordan Rift Valley. We then extended the analysis to a regional scale, investigating the drivers of the distribution using species distribution models. We found that similar ecological factors determined the distribution at both local and regional scales for A. nephilit. At a local scale, the species was found to preferentially occupy the outermost, illuminated, and warmer sectors of caves. Similarly, mean annual temperature, annual temperature range, and solar radiation were the most important drivers of its regional distribution. By investigating these two spatial scales simultaneously, we showed that it was possible to achieve an in-depth understanding of the environmental conditions that governs subterranean species distribution.

Phylogeny of a cosmopolitan family of morphologically conserved trapdoor spiders (Mygalomorphae, Ctenizidae) using Anchored Hybrid Enrichment, with a description of the family, Halonoproctidae Pocock 1901

The mygalomorph family Ctenizidae has a world-wide distribution and currently contains nine genera and 135 species. However, the monophyly of this group has long been questioned on both morphological and molecular grounds. Here, we use Anchored Hybrid Enrichment (AHE) to gather hundreds of loci from across the genome for reconstructing the phylogenetic relationships among the nine genera and test the monophyly of the family. We also reconstruct the possible ancestral ranges of the most inclusive clade recovered. Using AHE, we generate a supermatrix of 565 loci and 115,209 bp for 27 individuals. For the first time, analyses using all nine genera produce results definitively establishing the non-monophyly of Ctenizidae. A lineage formed exclusively by representatives of South African Stasimopus was placed as the sister group to the remaining taxa in the tree, and the Mediterranean Cteniza and Cyrtocarenum were recovered with high support as sister to exemplars of Euctenizidae, Migidae, and Idiopidae. All the remaining genera-Bothriocyrtum, Conothele, Cyclocosmia, Hebestatis, Latouchia, and Ummidia-share a common ancestor. Based on these results, we formally elevate this clade to the level of family. Our results definitively establish both the non-monophyly of the Ctenizidae and non-validity of the subfamilies Ummidiinae and Ctenizinae. In order to establish the placement of the remaining three ctenizid genera, Cteniza, Cyrtocarenum, and Stasimopus, thorough analyses within the context of a complete mygalomorph phylogenetic framework are needed. We formally describe the family Halonoproctidae Pocock 1901 and infer that the family's most recent common ancestor was likely distributed in western North America and Asia.

Spiny trapdoor spiders (Euoplos) of eastern Australia: Broadly sympatric clades are differentiated by burrow architecture and male morphology

Spiders of the infraorder Mygalomorphae are fast becoming model organisms for the study of biogeography and speciation. However, these spiders can be difficult to study in the absence of fundamental life history information. In particular, their cryptic nature hinders comprehensive sampling, and linking males with conspecific females can be challenging. Recently discovered differences in burrow entrance architecture and male morphology indicated that these challenges may have impeded our understanding of the trapdoor spider genus Euoplos in Australia's eastern mesic zone. We investigated the evolutionary significance of these discoveries using a multi-locus phylogenetic approach. Our results revealed the existence of a second, previously undocumented, lineage of Euoplos in the eastern mesic zone. This new lineage occurs in sympatry with a lineage previously known from the region, and the two are consistently divergent in their burrow entrance architecture and male morphology, revealing the suitability of these characters for use in phylogenetic studies. Divergent burrow entrance architecture and observed differences in microhabitat preferences are suggested to facilitate sympatry and syntopy between the lineages. Finally, by investigating male morphology and plotting it onto the phylogeny, we revealed that the majority of Euoplos species remain undescribed, and that males of an unnamed species from the newly discovered lineage had historically been linked, erroneously, to a described species from the opposite lineage. This paper clarifies the evolutionary relationships underlying life history diversity in the Euoplos of eastern Australia, and provides a foundation for urgently needed taxonomic revision of this genus.

Species conservation profile of the rare and endemic trapdoor spider Calathotarsus simoni (Araneae, Migidae) from Central Argentina

Background

Calathotarsussimoni Schiapelli & Gerschman 1975 is the only species of Migidae in Argentina. It is a rare and endemic spider only found in relict grassland of mountain systems in the province of Buenos Aires. This species is a habitat specialist spider occupying specific areas with certain microclimatic conditions on hilly and rocky grassland areas at about 500-1500 meters above sea level.

New information

The observed extent of occurrence (EOO) is 7207 km² and the area of occupancy (AOO) is 16 km². Two locations are identified based on the threat event related to the invasion of the species habitat by alien woody plants. In addition, intensive cattle production and agriculture also constitute relevant threats to the species.