Around the World in Eight Million Years: Historical Biogeography and Evolution of the Spray Zone Spider Amaurobioides (Araneae: Anyphaenidae)

Infrequent Long-Range Dispersal and Evolution of a Top Terrestrial Arthropod Predator in the Sub-Antarctic

AbstractThe sub-Antarctic terrestrial ecosystems survive on isolated oceanic islands in the path of circumpolar currents and winds that have raged for more than 30 million years and are shaped by climatic cycles that surpass the tolerance limits of many species. Surprisingly little is known about how these ecosystems assembled their native terrestrial fauna and how such processes have changed over time. Here, we demonstrate the patterns and timing of colonization and speciation in the largest and dominant arthropod predators in the eastern sub-Antarctic: spiders of the genus Myro. Our results indicate that this lineage originated from Australia before the Plio-Pleistocenic glacial cycles and underwent an adaptive radiation on the Crozet archipelago, from where one native species colonized multiple remote archipelagos via the Antarctic circumpolar current across thousands of kilometers. The results indicate limited natural connectivity between terrestrial macroinvertebrate faunas in the eastern sub-Antarctic and partial survival of repeated glaciations in the Plio-Pleistocene. Furthermore, our findings highlight that by integrating arthropod taxa from multiple continents, the climatically more stable volcanic Crozet archipelago played a critical role in the evolution and distribution of arthropod life in the sub-Antarctic.

The challenging biogeography of the Juan Fernández Islands and Coast Range of central Chile explained by new models of East Pacific tectonics

Biogeographers have often been puzzled by several unusual features in the Juan Fernández Islands (JFI) biota. These include the very high endemism density, multiple endemics that are older than the current islands, close biogeographic affinities with the central and West Pacific, and affinities with the diverse Coast Range of central Chile. We review aspects of biogeography in the JFI and the Coast Range in light of recent geological studies. These have examined the mantle below the East Pacific and South America, and have produced radical, new ideas on tectonic history. A long-lived, intraoceanic archipelago ~9000 km long is now thought to have existed in the East Pacific (passing between the JFI hotspot and mainland Chile) until the mid-Cretaceous. At this time, South America, which was moving westward with the opening of the Atlantic, collided with the archipelago. The assumption that the JFI biota is no older than its current islands is questionable, as taxa would have survived on prior islands produced at the JFI hotspot. We propose a new interpretation of evolution in the region based on tectonics rather than on island age and incorporating the following factors: the newly described East Pacific Archipelago; a long history for the JFI hotspot; metapopulation dynamics, including metapopulation vicariance; and formation of the Humboldt Current in the Cretaceous. The model accounts for many distinctive features of the JFI and Coast Range biota.

Phylogenomics illuminates the evolution of orb webs, respiratory systems and the biogeographic history of the world's smallest orb-weaving spiders (Araneae, Araneoidea, Symphytognathoids)

The miniature orb weaving spiders (symphytognathoids) are a group of small spiders (< 2 mm), including the smallest adult spider Patu digua (0.37 mm in body length), that have been classified into five families. The species of one of its constituent lineages, the family Anapidae, build a remarkable diversity of webs (ranging from orbs to sheet webs and irregular tangles) and even include a webless kleptoparasitic species. Anapids are also exceptional because of the extraordinary diversity of their respiratory systems. The phylogenetic relationships of symphytognathoid families have been recalcitrant with different classes of data, such as, monophyletic with morphology and its concatenation with Sanger-based six markers, paraphyletic (including a paraphyletic Anapidae) with solely Sanger-based six markers, and polyphyletic with transcriptomes. In this study, we capitalized on a large taxonomic sampling of symphytognathoids, focusing on Anapidae, and using de novo sequenced ultraconserved elements (UCEs) combined with UCEs recovered from available transcriptomes and genomes. We evaluated the conflicting relationships using a variety of support metrics and topology tests. We found support for the phylogenetic hypothesis proposed using morphology to obtain the "symphytognathoids'' clade, Anterior Tracheal System (ANTS) Clade and monophyly of the family Anapidae. Anapidae can be divided into three major lineages, the Vichitra Clade (including Teutoniella, Holarchaea, Sofanapis and Acrobleps), the subfamily Micropholcommatinae and the Orb-weaving anapids (Owa) Clade. Biogeographic analyses reconstructed a hypothesis of multiple long-distance transoceanic dispersal events, potentially influenced by the Antarctic Circumpolar Current and West Wind Drift. In symphytognathoids, the ancestral anterior tracheal system transformed to book lungs four times and reduced book lungs five times. The posterior tracheal system was lost six times. The orb web structure was lost four times independently and transformed into sheet web once.

Biogeography and eye size evolution of the ogre-faced spiders

Net-casting spiders (Deinopidae) comprise a charismatic family with an enigmatic evolutionary history. There are 67 described species of deinopids, placed among three genera, Deinopis, Menneus, and Asianopis, that are distributed globally throughout the tropics and subtropics. Deinopis and Asianopis, the ogre-faced spiders, are best known for their giant light-capturing posterior median eyes (PME), whereas Menneus does not have enlarged PMEs. Molecular phylogenetic studies have revealed discordance between morphology and molecular data. We employed a character-rich ultra-conserved element (UCE) dataset and a taxon-rich cytochrome-oxidase I (COI) dataset to reconstruct a genus-level phylogeny of Deinopidae, aiming to investigate the group's historical biogeography, and examine PME size evolution. Although the phylogenetic results support the monophyly of Menneus and the single reduction of PME size in deinopids, these data also show that Deinopis is not monophyletic. Consequently, we formally transfer 24 Deinopis species to Asianopis; the transfers comprise all of the African, Australian, South Pacific, and a subset of Central American and Mexican species. Following the divergence of Eastern and Western deinopids in the Cretaceous, Deinopis/Asianopis dispersed from Africa, through Asia and into Australia with its biogeographic history reflecting separation of Western Gondwana as well as long-distance dispersal events.

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.

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.

The fossil record of spiders revisited: implications for calibrating trees and evidence for a major faunal turnover since the Mesozoic

Studies in evolutionary biology and biogeography increasingly rely on the estimation of dated phylogenetic trees using molecular clocks. In turn, the calibration of such clocks is critically dependent on external evidence (i.e. fossils) anchoring the ages of particular nodes to known absolute ages. In recent years, a plethora of new fossil spiders, especially from the Mesozoic, have been described, while the number of studies presenting dated spider phylogenies based on fossil calibrations increased sharply. We critically evaluate 44 of these studies, which collectively employed 67 unique fossils in 180 calibrations. Approximately 54% of these calibrations are problematic, particularly regarding unsupported assignment of fossils to extant clades (44%) and crown (rather than stem) dating (9%). Most of these cases result from an assumed equivalence between taxonomic placement of fossils and their phylogenetic position. To overcome this limitation, we extensively review the literature on fossil spiders, with a special focus on putative synapomorphies and the phylogenetic placement of fossil species with regard to their importance for calibrating higher taxa (families and above) in the spider tree of life. We provide a curated list including 41 key fossils intended to be a basis for future estimations of dated spider phylogenies. In a second step, we use a revised set of 23 calibrations to estimate a new dated spider tree of life based on transcriptomic data. The revised placement of key fossils and the new calibrated tree are used to resolve a long-standing debate in spider evolution - we tested whether there has been a major turnover in the spider fauna between the Mesozoic and Cenozoic. At least 17 (out of 117) extant families have been recorded from the Cretaceous, implying that at least 41 spider lineages in the family level or above crossed the Cretaeous-Paleogene (K-Pg) boundary. The putative phylogenetic affinities of families known only from the Mesozoic suggest that at least seven Cretaceous families appear to have no close living relatives and might represent extinct lineages. There is no unambiguous fossil evidence of the retrolateral tibial apophysis clade (RTA-clade) in the Mesozoic, although molecular clock analyses estimated the major lineages within this clade to be at least ∼100 million years old. Our review of the fossil record supports a major turnover showing that the spider faunas in the Mesozoic and the Cenozoic are very distinct at high taxonomic levels, with the Mesozoic dominated by Palpimanoidea and Synspermiata, while the Cenozoic is dominated by Araneoidea and RTA-clade spiders.

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.

The Grass was Greener: Repeated Evolution of Specialized Morphologies and Habitat Shifts in Ghost Spiders Following Grassland Expansion in South America

While grasslands, one of Earth's major biomes, are known for their close evolutionary ties with ungulate grazers, these habitats are also paramount to the origins and diversification of other animals. Within the primarily South American spider subfamily Amaurobioidinae (Anyphaenidae), several species are found living in the continent's grasslands, with some displaying putative morphological adaptations to dwelling unnoticed in the grass blades. Herein, a dated molecular phylogeny provides the backbone for analyses revealing the ecological and morphological processes behind these spiders' grassland adaptations. The multiple switches from Patagonian forests to open habitats coincide with the expansion of South America's grasslands during the Miocene, while the specialized morphology of several grass-dwelling spiders originated at least three independent times and is best described as the result of different selective regimes operating on macroevolutionary timescales. Although grass-adapted lineages evolved towards different peaks in adaptive landscape, they all share one characteristic: an anterior narrowing of the prosoma allowing spiders to extend the first two pairs of legs, thus maintaining a slender resting posture in the grass blade. By combining phylogenetic, morphological, and biogeographic perspectives we disentangle multiple factors determining the evolution of a clade of terrestrial invertebrate predators alongside their biomes.

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

The Migidae are a family of austral trapdoor spiders known to show a highly restricted and disjunct distribution pattern. Here, we aim to investigate the phylogeny and historical biogeography of the group, which was previously thought to be vicariant in origin, and examine the biogeographic origins of the genus Moggridgea using a dated multi-gene phylogeny. Moggridgea specimens were sampled from southern Australia and Africa, and Bertmainus was sampled from Western Australia. Sanger sequencing methods were used to generate a robust six marker molecular dataset consisting of the nuclear genes 18S rRNA, 28S rRNA, ITS rRNA, XPNPEP3 and H3 and the mitochondrial gene COI. Bayesian and Maximum Likelihood methods were used to analyse the dataset, and the key dispersal nodes were dated using BEAST. Based on our data, we demonstrate that Moggridgea rainbowi from Kangaroo Island, Australia is a valid member of the otherwise African genus Moggridgea. Molecular clock dating analyses show that the inter-specific divergence of M. rainbowi from African congeners is between 2.27-16.02 million years ago (Mya). This divergence date significantly post-dates the separation of Africa from Gondwana (95 Mya) and therefore does not support a vicariant origin for Australian Moggridgea. It also pre-dates human colonisation of Kangaroo Island, a result which is further supported by the intra-specific divergence date of 1.10-6.39 Mya between separate populations on Kangaroo Island. These analyses provide strong support for the hypothesis that Moggridgea colonised Australia via long-distance trans-Indian Ocean dispersal, representing the first such documented case in a mygalomorph spider.