ORCID Profile
0000-0002-2328-9084
Current Organisation
University of Wisconsin Madison
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Publisher: Oxford University Press (OUP)
Date: 02-2022
Abstract: Deciphering the evolutionary relationships of Chelicerata (arachnids, horseshoe crabs, and allied taxa) has proven notoriously difficult, due to their ancient rapid radiation and the incidence of elevated evolutionary rates in several lineages. Although conflicting hypotheses prevail in morphological and molecular data sets alike, the monophyly of Arachnida is nearly universally accepted, despite historical lack of support in molecular data sets. Some phylotranscriptomic analyses have recovered arachnid monophyly, but these did not s le all living orders, whereas analyses including all orders have failed to recover Arachnida. To understand this conflict, we assembled a data set of 506 high-quality genomes and transcriptomes, s ling all living orders of Chelicerata with high occupancy and rigorous approaches to orthology inference. Our analyses consistently recovered the nested placement of horseshoe crabs within a paraphyletic Arachnida. This result was insensitive to variation in evolutionary rates of genes, complexity of the substitution models, and alternative algorithmic approaches to species tree inference. Investigation of sources of systematic bias showed that genes and sites that recover arachnid monophyly are enriched in noise and exhibit low information content. To test the impact of morphological data, we generated a 514-taxon morphological data matrix of extant and fossil Chelicerata, analyzed in tandem with the molecular matrix. Combined analyses recovered the clade Merostomata (the marine orders Xiphosura, Eurypterida, and Chasmataspidida), but merostomates appeared nested within Arachnida. Our results suggest that morphological convergence resulting from adaptations to life in terrestrial habitats has driven the historical perception of arachnid monophyly, paralleling the history of numerous other invertebrate terrestrial groups.
Publisher: Springer Science and Business Media LLC
Date: 21-05-2018
Publisher: Cold Spring Harbor Laboratory
Date: 24-10-2022
DOI: 10.1101/2022.10.22.513338
Abstract: Considerable progress has been achieved in resolving higher-level relationships of Arthropoda in the past two decades, largely precipitated by advances in sequencing technology. Yet, dark branches persist in the arthropod tree of life, principally among groups that are difficult to collect, occur in cryptic habitats, or are characterized by minute body size. Among chelicerates, the meso erse order Solifugae (commonly called camel spiders or sun spiders) is one of the last orders of Arachnida that lacks a higher-level phylogeny altogether and has long been characterized as one of the “neglected cousins”, a lineage of arachnid orders that are comparatively poorly studied with respect to evolutionary relationships. Though renowned for their aggression, remarkable running speed, and adaptation to arid habitats, inferring solifuge relationships has been hindered by inaccessibility of diagnostic characters in most ontogenetic stages for morphological datasets, whereas molecular investigations to date have been limited to one of the 12 recognized families. In this study we generated a phylogenomic dataset via capture of ultraconserved elements (UCEs) and s led all extant families. We recovered a well-resolved phylogeny of solifuge families, with two distinct groups of New World taxa nested within a broader Paleotropical radiation. To provide a temporal context to solifuge ersification, we estimated molecular ergence times using fossil calibrations within a least-squares framework. Solifugae were inferred to have radiated by the Permian, with ergences of most families dating to the post Paleogene-Cretaceous extinction. These results accord with a ersification history largely driven by vicariance as a result of continental breakup.
Publisher: Springer Science and Business Media LLC
Date: 14-06-2021
DOI: 10.1007/S00427-021-00678-9
Abstract: The homology of the arachnid chelicera with respect to other head appendages in Panarthropoda has long been debated. Gene expression data and the re-interpretation of early transitional fossils have supported the homology of the deutocerebrum and its associated appendages, implying a homology between primary antennae (mandibulates), chelicerae (euchelicerates), and chelifores (sea spiders). Nevertheless, comparatively little is known about the mechanistic basis of proximo-distal (PD) axis induction in chelicerates, much less the basis for cheliceral fate specification. Here, we describe a new cheliceral teratology in the spider Tetragnatha versicolor Walckenaer, 1841, which consists on a duplication of the PD axis of the left chelicera associated with a terminal secondary schistomely on the fang of the lower axis. This duplication offers clues as to potential shared mechanisms of PD axis formation in the chelicera. We review the state of knowledge on PD axis induction mechanisms in arthropods and identify elements of gene regulatory networks that are key for future functional experiments of appendage development in non-insect model systems. Such investigations would allow a better understanding of PD axis induction of modified and poorly studied arthropod limbs (e.g., chelicerae, chelifores, and ovigers).
Publisher: MDPI AG
Date: 02-06-2023
DOI: 10.20944/PREPRINTS202306.0212.V1
Abstract: The location of Israel at the junction of three continents leads to a unique faunal combination of Palearctic and Afrotropic zoogeographic origins. Following systematic revisions over the past sixty years and the discovery of new species, the only available key to the pseudoscorpions (Arachnida: Pseudoscorpiones) of Israel (Beier 1963) has become outdated. We provide here an up-to-date checklist of the pseudoscorpion species of Israel including distribution maps, and the first illustrated identification key of the Israeli fauna based on morphological characters. Prior to our study this fauna comprised twelve families, 26 genera and 52 morphospecies, including several “subspecies”. We increase this number and list 61 pseudoscorpion morphospecies that belong to 28 genera and fourteen families. Most species are Palearctic and Mediterranean, and only a few are Afrotropic. Two families new to Israel are reported here for the first time: Syarinidae and Cheiridiidae. Both families are cosmopolitan and have representatives in the Mediterranean region. The putative new species are presented here at a genus level and will be described separately elsewhere.
Publisher: Oxford University Press (OUP)
Date: 28-03-2022
Abstract: Scorpions constitute a charismatic lineage of arthropods and comprise more than 2500 described species. Found throughout various tropical and temperate habitats, these predatory arachnids have a long evolutionary history, with a fossil record that began in the Silurian. While all scorpions are venomous, the asymmetrically erse family Buthidae harbors nearly half the ersity of extant scorpions, and all but one of the 58 species that are medically significant to humans. However, the lack of a densely s led scorpion phylogeny has hindered broader inferences of the ersification dynamics of scorpion toxins. To redress this gap, we assembled a phylogenomic data set of 100 scorpion venom gland transcriptomes and genomes, emphasizing the s ling of highly toxic buthid genera. To infer ergence times of venom gene families, we applied a phylogenomic node dating approach for the species tree in tandem with phylostratigraphic bracketing to estimate the minimum ages of mammal-specific toxins. Our analyses establish a robustly supported phylogeny of scorpions, particularly with regard to relationships between medically significant taxa. Analysis of venom gene families shows that mammal-active sodium channel toxins (NaTx) have independently evolved in five lineages within Buthidae. Temporal windows of mammal-targeting toxin origins are correlated with the basal ersification of major scorpion mammal predators such as shrews, bats, and rodents. These results suggest an evolutionary model of relatively recent ersification of buthid NaTx homologs in response to the ersification of scorpion predators. [Adaptation arachnids phylogenomic dating phylostratigraphy venom.]
Publisher: MDPI AG
Date: 24-10-2023
Publisher: Oxford University Press (OUP)
Date: 10-02-2021
Abstract: Long-branch attraction is a systematic artifact that results in erroneous groupings of fast-evolving taxa. The combination of short, deep internodes in tandem with long-branch attraction artifacts has produced empirically intractable parts of the Tree of Life. One such group is the arthropod subphylum Chelicerata, whose backbone phylogeny has remained unstable despite improvements in phylogenetic methods and genome-scale data sets. Pseudoscorpion placement is particularly variable across data sets and analytical frameworks, with this group either clustering with other long-branch orders or with Arachnopulmonata (scorpions and tetrapulmonates). To surmount long-branch attraction, we investigated the effect of taxonomic s ling via sequential deletion of basally branching pseudoscorpion superfamilies, as well as varying gene occupancy thresholds in supermatrices. We show that concatenated supermatrices and coalescent-based summary species tree approaches support a sister group relationship of pseudoscorpions and scorpions, when more of the basally branching taxa are s led. Matrix completeness had demonstrably less influence on tree topology. As an external arbiter of phylogenetic placement, we leveraged the recent discovery of an ancient genome duplication in the common ancestor of Arachnopulmonata as a litmus test for competing hypotheses of pseudoscorpion relationships. We generated a high-quality developmental transcriptome and the first genome for pseudoscorpions to assess the incidence of arachnopulmonate-specific duplications (e.g., homeobox genes and miRNAs). Our results support the inclusion of pseudoscorpions in Arachnopulmonata (new definition), as the sister group of scorpions. Panscorpiones (new name) is proposed for the clade uniting Scorpiones and Pseudoscorpiones.
Publisher: MDPI AG
Date: 18-05-2018
Publisher: Elsevier BV
Date: 05-2018
DOI: 10.1016/J.YMPEV.2018.01.003
Abstract: The scorpion family Bothriuridae occupies a subset of landmasses formerly constituting East and West temperate Gondwana, but its relationship to other scorpion families is in question. Whereas morphological data have strongly supported a sister group relationship of Bothriuridae and the superfamily Scorpionoidea, a recent phylogenomic analysis recovered a basal placement of bothriurids within Iurida, albeit s ling only a single exemplar. Here we reexamined the phylogenetic placement of the family Bothriuridae, s ling six bothriurid exemplars representing both East and West Gondwana, using transcriptomic data. Our results demonstrate that the sister group relationship of Bothriuridae to the clade ("Chactoidea" + Scorpionoidea) is supported by the inclusion of additional bothriurid taxa, and that this placement is insensitive to matrix completeness or partitioning by evolutionary rate. We also estimated ergence times within the order Scorpiones using multiple fossil calibrations, to infer whether the family Bothriuridae is sufficiently old to be characterized as a true Gondwanan lineage. We show that scorpions underwent ancient ersification between the Devonian and early Carboniferous. The age interval of the bothriurids s led (a derived group that excludes exemplars from South Africa) spans the timing of breakup of temperate Gondwana.
Publisher: CSIRO Publishing
Date: 2020
DOI: 10.1071/IS20022
Abstract: Southern Australian waters feature remarkably erse assemblages of the sea spider family Callipallenidae Hilton, 1942. The most speciose of the three Australian-endemic genera currently recognised has been known as Meridionale Staples, 2014, but is here reinstated under the name Pallenella Schimkewitsch, 1909 based on its type species Pallenella laevis (Hoek, 1881). This genus includes several brightly coloured forms that occur in high abundance on arborescent bryozoans. However, considerable similarity of congeners and scarcity of diagnostic characters continue to render species delineation in this genus challenging. Using an integrative taxonomic approach, we combine detailed morphological investigation with analysis of two genetic markers (mitochondrial cytochrome c oxidase subunit I, and nuclear rDNA including internal transcribed spacers 1 and 2) to explore the extraordinary species richness of the genus Pallenella in south-east Tasmania. In agreement with our morphology-based segregation of different species and morphotypes, we recovered well-supported corresponding clades in the genetic analyses. Strong mito-nuclear concordance in the two markers supports the inference of sustained reproductive isolation between the sympatrically occurring forms. Based on these findings, we distinguish a total of 13 Tasmanian congeners, representing the most erse assemblage of sympatric species in the same microhabitat reported for a single pycnogonid genus. Within this assemblage, we (1) record the type species P. laevis for the first time after almost 150 years, (2) delineate the two Tasmanian morphotypes of the provisional ‘variabilis’ complex, and (3) describe two species new to science (P. karenae, sp. nov., P. baroni, sp. nov.). Despite considerable genetic ergences between most congeners, only few and often subtle characters are found to be suitable for morphology-based delineation. Notably, colouration of living specimens is suggested to be informative in some cases. For morphology-based species identification of preserved specimens, a key relying on combinations of characters rather than single diagnostic features is proposed.
Publisher: Oxford University Press (OUP)
Date: 26-03-2014
Abstract: Relationships between the five extant orders of centipedes have been considered solved based on morphology. Phylogenies based on s les of up to a few dozen genes have largely been congruent with the morphological tree apart from an alternative placement of one order, the relictual Craterostigmomorpha, consisting of two species in Tasmania and New Zealand. To address this incongruence, novel transcriptomic data were generated to s le all five orders of centipedes and also used as a test case for studying gene-tree incongruence. Maximum likelihood and Bayesian mixture model analyses of a data set composed of 1,934 orthologs with 45% missing data, as well as the 389 orthologs in the least saturated, stationary quartile, retrieve strong support for a sister-group relationship between Craterostigmomorpha and all other pleurostigmophoran centipedes, of which the latter group is newly named Amalpighiata. The Amalpighiata hypothesis, which shows little gene-tree incongruence and is robust to the influence of among-taxon compositional heterogeneity, implies convergent evolution in several morphological and behavioral characters traditionally used in centipede phylogenetics, such as maternal brood care, but accords with patterns of first appearances in the fossil record.
Location: United States of America
No related grants have been discovered for Prashant Sharma.