Molecular phylogeny of the spider family Sparassidae with focus on the genus Eusparassus and notes on the RTA-clade and 'Laterigradae'

Advances in the reconstruction of the spider tree of life: A roadmap for spider systematics and comparative studies

In the last decade and a half, advances in genetic sequencing technologies have revolutionized systematics, transforming the field from studying morphological characters or a few genetic markers, to genomic datasets in the phylogenomic era. A plethora of molecular phylogenetic studies on many taxonomic groups have come about, converging on, or refuting prevailing morphology or legacy-marker-based hypotheses about evolutionary affinities. Spider systematics has been no exception to this transformation and the inter-relationships of several groups have now been studied using genomic data. About 51 500 extant spider species have been described, all with a conservative body plan, but innumerable morphological and behavioural peculiarities. Inferring the spider tree of life using morphological data has been a challenging task. Molecular data have corroborated many hypotheses of higher-level relationships, but also resulted in new groups that refute previous hypotheses. In this review, we discuss recent advances in the reconstruction of the spider tree of life and highlight areas where additional effort is needed with potential solutions. We base this review on the most comprehensive spider phylogeny to date, representing 131 of the 132 spider families. To achieve this sampling, we combined six Sanger-based markers with newly generated and publicly available genome-scale datasets. We find that some inferred relationships between major lineages of spiders (such as Austrochiloidea, Palpimanoidea and Synspermiata) are robust across different classes of data. However, several new hypotheses have emerged with different classes of molecular data. We identify and discuss the robust and controversial hypotheses and compile this blueprint to design future studies targeting systematic revisions of these problematic groups. We offer an evolutionary framework to explore comparative questions such as evolution of venoms, silk, webs, morphological traits and reproductive strategies.

Taxonomic revision of the troglophile Spariolenus spiders (Araneae: Sparassidae) in South and West Asia

The taxonomy of the genus Spariolenus Simon, 1880 (Heteropodinae) is updated in its entire distribution range in South and West Asia. Newly collected specimens and historical museum material were studied, some date back to more than 124 years. Four new species are described as Spariolenus omidvarbrothers sp. n. (male, female) from southeastern Iran, S. baluchistanicus sp. n. (female) from Pakistan and, S. bakasura sp. n. (male, female) and S. kabandha sp. n. (female) from the Western Ghats and northern regions of India, respectively; specimens of the latter three species had been previously incorrectly identified as S. tigris Simon, 1880. Spariolenus lindbergi (Roewer, 1962) comb. nov. is transferred from the genus Heteropoda Latreille, 1804. We discovered and described its male for the first time, along with redescription of the female using recently collected material near the type locality from Afghanistan. Two species, Spariolenus mansourii Moradmand, 2017 (Iran) and S. secundus Jger, 2006 (Oman) are recorded from new geographic localities. A distribution map of all extant Spariolenus species with updated records is presented.

Revision of the huntsman spider genus Micrommata Latreille, 1804 (Sparassidae: Sparassinae)

The genus Micrommata Latreille, 1804 is revised and two new species are described: Micrommata biggi spec. nov. (male, female; Trkiye, Armenia, Iran, Turkmenistan), and M. diesenhoff spec. nov. (male, female; Sierra Leone). Micrommata aragonensis Urones, 2004 is synonymised with M. formosa Pavesi, 1878. All known species are redescribed and illustrated, and an identification key for males and females is provided for all true Micrommata species. A distribution map is provided for all species. M. formosa is for the first time recorded from Portugal, M. ligurina (C.L. Koch, 1845) from Morocco, the latter species having been introduced into United Kingdom and Germany. Micrommata darlingi Pocock, 1901 (female; Zimbabwe) is considered misplaced and probably related to the genus Eusparassus Simon, 1903. Functional copulatory mechanics are briefly discussed using -CT scans.

A novel probe set for the phylogenomics and evolution of RTA spiders

Spiders are important models for evolutionary studies of web building, sexual selection and adaptive radiation. The recent development of probes for UCE (ultra-conserved element)-based phylogenomic studies has shed light on the phylogeny and evolution of spiders. However, the two available UCE probe sets for spider phylogenomics (Spider and Arachnida probe sets) have relatively low capture efficiency within spiders, and are not optimized for the retrolateral tibial apophysis (RTA) clade, a hyperdiverse lineage that is key to understanding the evolution and diversification of spiders. In this study, we sequenced 15 genomes of species in the RTA clade, and using eight reference genomes, we developed a new UCE probe set (41 845 probes targeting 3802 loci, labelled as the RTA probe set). The performance of the RTA probes in resolving the phylogeny of the RTA clade was compared with the Spider and Arachnida probes through an in-silico test on 19 genomes. We also tested the new probe set empirically on 28 spider species of major spider lineages. The results showed that the RTA probes recovered twice and four times as many loci as the other two probe sets, and the phylogeny from the RTA UCEs provided higher support for certain relationships. This newly developed UCE probe set shows higher capture efficiency empirically and is particularly advantageous for phylogenomic and evolutionary studies of RTA clade and jumping spiders.

Ecological niche modelling and climate change in two species groups of huntsman spider genus Eusparassus in the Western Palearctic

The huntsman spiders' genus Eusparassus are apex arthropod predators in desert ecosystems of the Afrotropical and Palearctic ecoregions. The Eusparassus dufouri and E. walckenaeri clades are two distinct taxonomic, phylogenetic, and geographic units concerning morphology, molecular phylogeny, and spatial data; but little is known about their ecological niche. We applied the maximum-entropy approach and modelled ecologic niches of these two phylogenetically closely related clades. Ecological niches of the two clades were compared using identity and background tests and two different metrics, the Schooner's D and Warren's I. We also predicted the impacts of climate change on the distribution of the two clades. The results of the identity test showed that the ecological niches of the two clades were different in geographic space but were similar in environmental space. While results of the background test revealed that the ecological niches of the two clades were similar in geographic and environmental space. This indicated that "niche conservatism" had an important role over the evolutionary time of allopatric diversification. However, the normalized difference vegetation index vs. topographic heterogeneity had influenced the niches of the dufouri and walckenaeri clades, respectively. The analyses recovered that the two clades' climatically suitable habitats will increase under future climate (the year 2070). However, since the two clades are characterized by the narrow range of environmental optimum and the accordingly high limits of tolerance, they are vulnerable to climate change.

Combining genomic, phenotypic and Sanger sequencing data to elucidate the phylogeny of the two-clawed spiders (Dionycha)

The importance of morphology in the phylogenomic era has recently gained attention, but relatively few studies have combined both types of information when inferring phylogenetic relationships. Sanger sequencing legacy data can also be important for understanding evolutionary relationships. The possibility of combining genomic, morphological and Sanger data in one analysis seems compelling, permitting a more complete sampling and yielding a comprehensive view of the evolution of a group. Here we used these three data types to elucidate the systematics and evolution of the Dionycha, a highly diverse group of spiders relatively underrepresented in phylogenetic studies. The datasets were analyzed separately and combined under different inference methods, including a novel approach for analyzing morphological matrices with commonly used evolutionary models. We tested alternative hypotheses of relationships and performed simulations to investigate the accuracy of our findings. We provide a comprehensive and thorough phylogenetic hypothesis for Dionycha that can serve as a robust framework to test hypotheses about the evolution of key characters. We also show that morphological data might have a phylogenetic impact, even when massively outweighed by molecular data. Our approach to analyze morphological data may serve as an alternative to the proposed practice of arbitrarily partitioning, weighting, and choosing between parsimony and stochastic models. As a result of our findings, we propose Trachycosmidae new rank for a group of Australian genera formerly included in Trochanteriidae and Gallieniellidae, and consider Ammoxenidae as a junior synonym of Gnaphosidae. We restore the family rank for Prodidomidae, but transfer the subfamily Molycriinae to Gnaphosidae. Drassinella is transferred to Liocranidae, Donuea to Corinnidae, and Mahafalytenus to Viridasiidae.

A molecular phylogeny of the Chinese Sinopoda spiders (Sparassidae, Heteropodinae): implications for taxonomy

Sinopoda spiders are a diverse group with limited dispersal ability. They are remarkably sympatric among related species, which often results in misidentification and incorrect matching of sexes. In order to understand the evolutionary relationships and revise the taxonomy problems in this genus, we offer the first molecular phylogeny of Sinopoda. Our results strongly support the monophyly of Sinopoda and its sister relationship with Spariolenus and reject the monophyly of the S. okinawana species group. We establish three new species groups based on both molecular and morphological data. Our phylogeny also illuminates some taxonomic issues and clarifies some species limits: (1) Supporting the newly revised matching of sexes in S. longiducta and S. yaanensis by Zhong et al. (2019). (2) The original description of S. campanacea was based on mismatched sexes. S. changde is proposed as a junior synonymy of S. campanacea, while the original female 'S. campanacea' is here described as a new species: S. papilionaceous Liu sp. nov. (3) The type series of S. serpentembolus contains mismatched sexes. The female is considered as S. campanacea, while we here report the correctly matched females of S. serpentembolus. (4) We describe one additional new species: S. wuyiensis Liu sp. nov. Our first molecular phylogeny of Sinopoda provides a tool for comparative analyses and a solid base for the future biodiversity and taxonomic work on the genus.

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.

Sixteen new species of the genus Pseudopoda Jäger, 2000 from China, Myanmar, and Thailand (Sparassidae, Heteropodinae)

Sixteen new species of Pseudopoda Jäger, 2000 (Sparassidae, Heteropodinae) are described. Among them, eight species were collected from China: P.chayuensis Zhao & Li, sp. n. (♂), P.conaensis Zhao & Li, sp. n. (♂), P.medogensis Zhao & Li, sp. n. (♂), P.nyingchiensis Zhao & Li, sp. n. (♂), P.shacunensis Zhao & Li, sp. n. (♂), P.shuo Zhao & Li, sp. n. (♂♀), P.yuanjiangensis Zhao & Li, sp. n. (♀) and P.zixiensis Zhao & Li, sp. n. (♂); seven from Myanmar: P.colubrina Zhao & Li, sp. n. (♂♀), P.daxing Zhao & Li, sp. n. (♂), P.gexiao Zhao & Li, sp. n. (♂), P.putaoensis Zhao & Li, sp. n. (♂), P.subbirmanica Zhao & Li, sp. n. (♂♀), P.titan Zhao & Li, sp. n. (♂♀), P.xia Zhao & Li, sp. n. (♂); and one from Thailand: P.maeklongensis Zhao & Li, sp. n. (♂). A distribution map of the new species is also provided.

Gene flow and Andean uplift shape the diversification of Gasteracantha cancriformis (Araneae: Araneidae) in Northern South America

The Andean uplift has played a major role in shaping the current Neotropical biodiversity. However, in arthropods other than butterflies, little is known about how this geographic barrier has impacted species historical diversification. Here, we examined the phylogeography of the widespread color polymorphic spider Gasteracantha cancriformis to evaluate the effect of the northern Andean uplift on its divergence and assess whether its diversification occurred in the presence of gene flow. We inferred phylogenetic relationships and divergence times in G. cancriformis using mitochondrial and nuclear data from 105 individuals in northern South America. Genetic diversity, divergence, and population structure were quantified. We also compared multiple demographic scenarios for this species using a model-based approach (phrapl) to determine divergence with or without gene flow. At last, we evaluated the association between genetic variation and color polymorphism. Both nuclear and mitochondrial data supported two well-differentiated clades, which correspond to populations occurring on opposite sides of the Eastern cordillera of the Colombian Andes. The final uplift of this cordillera was identified as the most likely force that shaped the diversification of G. cancriformis in northern South America, resulting in a cis- and trans-Andean phylogeographic structure for the species. We also found shared genetic variation between the cis- and trans-Andean clades, which is better explained by a scenario of historical divergence in the face of gene flow. This has been likely facilitated by the presence of low-elevation passes across the Eastern Colombian cordillera. Our work constitutes the first example in which the Andean uplift coupled with gene flow influenced the evolutionary history of an arachnid lineage.

Wolf spider burrows from a modern saline sandflat in central Argentina: morphology, taphonomy and clues for recognition of fossil examples

Pavocosa sp. (Lycosidae) burrows found in an open sparsely vegetated area on the edge of the Gran Salitral saline lake, in central Argentina, are described. Burrows were studied by capturing the occupant and casting them with dental plaster. The hosting sediments and vegetation were also characterized. Inhabited Pavocosa sp. burrows display distinctive features as open, cylindrical, nearly vertical, silk lined shafts about 120 mm long, subcircular entrances, a gradual downward widening, and a particularly distinctive surface ornamentation in the form of sets of two linear parallel marks at a high angle to the burrow axis. Instead, casts of vacated Pavocosa sp. burrows showed some disturbances caused either by the reoccupation by another organism or by predation of the dweller. Two morphologies are related to reoccupation of burrows: those with a structure in form of an “umbrella” and another with smaller excavations at the bottom of the burrow. Predation by small mammals produces funnel-shaped burrows. Both active and abandoned Pavocosa sp. burrow casts are compared with existing ichnogenera and inorganic sedimentary structures, highlighting its distinction. It is argued that key features like the presence of a neck, a downward widening and the described surface texture will allow recognition of wolf spider burrows in the fossil record. However, the putative spider burrows described in the literature either lack the necessary preservational quality or do not show ornamentation similar to the modern wolf spider burrows. Fossil wolf spiders are recorded since the Paleogene (possibly Late Cretaceous), therefore Cenozoic continental rocks can contain wolf spider burrows awaiting recognition. In addition, the particular distribution of Pavocosa sp. in saline lakes may imply that this type of burrow is linked to saline environments.

Early Cretaceous greenhouse pumped higher taxa diversification in spiders

The Cretaceous experienced one of the most remarkable greenhouse periods in geological history. During this time, ecosystem reorganization significantly impacted the diversification of many groups of organisms. The rise of angiosperms marked a major biome turnover. Notwithstanding, relatively little remains known about how the Cretaceous global ecosystem impacted the evolution of spiders, which constitute one of the most abundant groups of predators. Herein, we evaluate the transcriptomes of 91 taxa representing more than half of the spider families. We add 23 newly sequenced taxa to the existing database to obtain a robust phylogenomic assessment. Phylogenetic reconstructions using different datasets and methods obtain novel placements of some groups, especially in the Synspermiata and the group having a retrolateral tibial apophysis (RTA). Molecular analyses indicate an expansion of the RTA clade at the Early Cretaceous with a hunting predatory strategy shift. Fossil analyses show a 7-fold increase of diversification rate at the same period, but this likely owes to the first occurrence of spiders in amber deposit. Additional analyses of fossil abundance show an accumulation of spider lineages in the Early Cretaceous. We speculate that the establishment of a warm greenhouse climate pumped the diversification of spiders, in particular among webless forms tracking the abundance of insect prey. Our study offers a new pathway for future investigations of spider phylogeny and diversification.

The origins of the Psechridae: Web-building lycosoid spiders

Psechrids are an enigmatic family of S.E. Asian spiders. This small family builds sheet webs and even orb webs, yet unlike other orb weavers, its putative relatives are largely cursorial lycosoids - a superfamily of approximately seven spider families related to wolf spiders. The orb web was invented at least twice: first in a very ancient event, and then second, within this clade of wolf-like spiders that reinvented this ability. Exactly how the spiders modified their silks, anatomy, and behaviors to accomplish this transition requires that we identify their precise evolutionary origins - yet, thus far, molecular phylogenies show poor support and considerable disagreement. Using phylogenomic methods based on whole body transcriptomes for psechrids and their putative relatives, we have recovered a well-supported phylogeny that places the Psechridae sister to the Ctenidae - a family of mostly cursorial habits but that, as with all psechrids, retains some cribellate species. Although this position reinforces the prevailing view that orb weaving in psechrids is largely a consequence of convergence, it is still possible that some components of this behavior are retained or resurrected in common with more distant true orb weaving ancestors.

An unexpected new species of the genus Pseudopoda (Araneae, Sparassidae, Heteropodinae) from the Western Ghats in India

A new species of the genus Pseudopoda is described from India: Pseudopodaashcharyasp. n. Males are characterised by the absence of the conductor and females are unique within the genus in having the lateral lobes of their epigyne fused. The systematic relationship of the new species is discussed referring to its isolated occurrence in the Western Ghats.