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  1. ; ; ; ; ; ; ( , Molecular Phylogenetics and Evolution)
    The systematics of the arachnid order Solifugae have been an enigma, owing to challenges in interpreting morphology, a paucity of molecular phylogenetic studies sampling across the group, and a dearth of taxonomic attention for many lineages. Recent work has suggested that solifuge families largely exhibit contiguous distributions and reflect patterns of vicariance, with the exception of three families: Melanoblossidae, Daesiidae and Gylippidae. Morphological studies have cast doubt on their existing circumscriptions and the present composition of these taxa renders their distributions as disjunct. We leveraged ultraconserved elements (UCEs) to test the phylogenetic placement of three key lineages of Solifugae that cause these anomalous distributions: Dinorhax rostrumpsittaci (putative melanoblossid), Namibesia (putative daesiid), and Trichotoma (putative gylippid). Phylogenetic placement of these three genera based on UCEs rendered the families that harbor them as para- or polyphyletic, recovering instead relationships that better accord with a biogeographic history driven by vicariance. Toward a stable and phylogenetically informed classification of Solifugae, we establish three new families, Dinorhaxidae new rank, Namibesiidae new rank and Lipophagidae new rank. 
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  2. ; ; ( , Molecular Phylogenetics and Evolution)
    Opiliones (harvestmen) have come to be regarded as an abundant source of model groups for study of historical biogeography, due to their ancient age, poor dispersal capability, and high fidelity to biogeographic terranes. One of the least understood harvestman groups is the Paleotropical Assamiidae, one of the more diverse families of Opiliones. Due to a labyrinthine taxonomy, poorly established generic and subfamilial boundaries, and the lack of taxonomic keys for the group, few efforts have been undertaken to decipher relationships within this arachnid lineage. Neither the monophyly of the family, nor its exact placement in the harvestman phylogeny, have been established. Here, we assessed the internal phylogeny of Assamiidae using a ten-locus Sanger dataset, sampling key lineages putatively ascribed to this family for five of the ten markers. Our analyses recovered Assamiidae as a monophyletic group, in a clade with the primarily Afrotropical Pyramidopidae and the southeast Asian Beloniscidae. Internal relationships of assamiids disfavored the systematic validity of subfamilies, with biogeography reflecting much better phylogenetic structure than the existing higher-level taxonomy. To assess whether the Asian assamiids came to occupy Indo-Pacific terranes via rafting on the Indian subcontinent, we performed divergence dating to infer the age of the family. Our results show that Indo-Pacific clades are ancient, originating well before the Cretaceous and therefore predate a vicariant mechanism commonly encountered for Paleotropical taxa. 
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  3. ; ; ( , Microbiology Resource Announcements)
    Newton, Irene L. (Ed.)
    Here, we report the draft genome and annotation of Candidatus Nardonella dryophthoridicola strain NARMHE1, obtained via Oxford Nanopore sequencing of the ovaries of its host, the weevil Metamasius hemipterus, from a population from southeast Brazil. 
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  4. ; ; ; ; ; ( , Molecular Biology and Evolution)
    True, John (Ed.)
    Despite an abundance of gene expression surveys, comparatively little is known about Hox gene function in Chelicerata. Previous investigations of paralogs of labial (lab) and Deformed (Dfd) in a spider have shown that these play a role in tissue maintenance of the pedipalp segment (lab-1) and in patterning the first walking leg identity (Dfd-1), respectively. However, extrapolations of these data across chelicerates are hindered by the existence of duplicated Hox genes in arachnopulmonates (e.g., spiders and scorpions), which have resulted from an ancient whole genome duplication (WGD) event. Here, we investigated the function of the single-copy ortholog of lab in the harvestman Phalangium opilio, an exemplar of a lineage that was not subject to this WGD. Embryonic RNA interference against lab resulted in two classes of phenotypes: homeotic transformations of pedipalps to chelicerae, as well as reduction and fusion of the pedipalp and leg 1 segments. To test for combinatorial function, we performed a double knockdown of lab and Dfd, which resulted in a homeotic transformation of both pedipalps and the first walking legs into cheliceral identity, whereas the second walking leg is transformed into a pedipalpal identity. Taken together, these results elucidate a model for the Hox logic of head segments in Chelicerata. To substantiate the validity of this model, we performed expression surveys for lab and Dfd paralogs in scorpions and horseshoe crabs. We show that repetition of morphologically similar appendages is correlated with uniform expression levels of the Hox genes lab and Dfd, irrespective of the number of gene copies. 
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  5. ; ; ; ; ; ; ; ; ; ; et al ( , iScience)
    Advanced sequencing technologies have expedited resolution of higher-level arthropod relationships. Yet, dark branches persist, principally among groups occurring in cryptic habitats. Among chelicerates, Solifugae ("camel spiders") is the last order lacking a higher-level phylogeny and have thus been historically characterized as "neglected [arachnid] cousins". Though renowned for aggression, remarkable running speed, and xeric adaptation, inferring solifuge relationships has been hindered by inaccessibility of diagnostic morphological characters, whereas molecular investigations have been limited to one of 12 recognized families. Our phylogenomic dataset via capture of ultraconserved elements sampling all extant families recovered a well-resolved phylogeny, with two distinct groups of New World taxa nested within a broader Paleotropical radiation. Divergence times using fossil calibrations inferred that Solifugae radiated by the Permian, and most families diverged prior to the Paleogene-Cretaceous extinction, likely driven by continental breakup. We establish Boreosolifugae new suborder uniting five Laurasian families, and Australosolifugae new suborder uniting seven Gondwanan families using morphological and biogeographic signal. 
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  6. ; ; ( , Molecular Phylogenetics and Evolution)
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  7. ; ; ; ( , Cladistics)
    Abstract

    Scorpions are ancient and historically renowned for their potent venom. Traditionally, the systematics of this group of arthropods was supported by morphological characters, until recent phylogenomic analyses (using RNAseq data) revealed most of the higher‐level taxa to be non‐monophyletic. While these phylogenomic hypotheses are stable for almost all lineages, some nodes have been hard to resolve due to minimal taxonomic sampling (e.g. family Chactidae). In the same line, it has been shown that some nodes in the Arachnid Tree of Life show disagreement between hypotheses generated using transcritptomes and other genomic sources such as the ultraconserved elements (UCEs). Here, we compared the phylogenetic signal of transcriptomes vs. UCEs by retrieving UCEs from new and previously published scorpion transcriptomes and genomes, and reconstructed phylogenies using both datasets independently. We reexamined the monophyly and phylogenetic placement of Chactidae, sampling an additional chactid species using both datasets. Our results showed that both sets of genome‐scale datasets recovered highly similar topologies, with Chactidae rendered paraphyletic owing to the placement ofNullibrotheas allenii. As a first step toward redressing the systematics of Chactidae, we establish the family Anuroctonidae (new family) to accommodate the genusAnuroctonus.

     
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  8. ; ; ; ; ; ; ( , Frontiers in Zoology)
    Abstract Background

    The comparative embryology of Chelicerata has greatly advanced in recent years with the integration of classical studies and genetics, prominently spearheaded by developmental genetic works in spiders. Nonetheless, the understanding of the evolution of development and polarization of embryological characters in Chelicerata is presently limited, as few non-spider species have been well studied. A promising focal species for chelicerate evo-devo is the daddy-long-legs (harvestman)Phalangium opilio, a member of the order Opiliones.Phalangium opilio, breeds prolifically and is easily accessible in many parts of the world, as well as tractable in a laboratory setting. Resources for this species include developmental transcriptomes, a draft genome, and protocols for RNA interference, but a modern staging system is critically missing for this emerging model system.

     Results

    We present a staging system ofP. opilioembryogenesis that spans the most important morphogenetic events with respect to segment formation, appendage elongation and head development. Using time-lapse imaging, confocal microscopy, colorimetric in situ hybridization, and immunohistochemistry, we tracked the development of synchronous clutches from egg laying to adulthood. We describe key events in segmentation, myogenesis, neurogenesis, and germ cell formation.

     Conclusion

    Considering the phylogenetic position of Opiliones and the unduplicated condition of its genome (in contrast to groups like spiders and scorpions), this species is poised to serve as a linchpin for comparative studies in arthropod development and genome evolution. The staging system presented herein provides a valuable reference forP.opiliothat we anticipate being useful to the arthropod evo-devo community, with the goal of revitalizing research in the comparative development of non-spider arachnids.

     
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  9. ; ; ( , Invertebrate Systematics)
    null (Ed.)
    The Cyphophthalmi genus Troglosiro (the only genus of the family Troglosironidae) is endemic to New Caledonia, representing one of the oldest lineages of this emerged part of Zealandia. Its species are short-range endemics, many known from single localities. Here we examined the phylogenetic relationships of Troglosironidae using standard Sanger-sequenced markers (nuclear 18S rRNA, 28S rRNA, and mitochondrial 16S rRNA and cytochrome c oxidase subunit I) and a combination of phylogenetic methods, including parsimony under Direct Optimization and maximum likelihood with static homology. We also applied a diversity of species delimitation methods, including distance-based, topology-based and unsupervised machine learning to evaluate previous species designations. Finally, we used a combination of genetic and morphological information to describe four new species – T. dogny sp. nov., T. pin sp. nov., T. pseudojuberthiei sp. nov. and T. sharmai sp. nov. – and discuss them in the broader context of the phylogeny and biogeographic history of the family. A key to the species of Troglosiro is also provided.urn:lsid:zoobank.org:pub:93541314-8309-468C-BB77-B34C3A81137E 
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  10. ; ; ; ; ; ; ; ; ( , Proceedings of the Royal Society B: Biological Sciences)
    null (Ed.)
    Chelicerate arthropods exhibit dynamic genome evolution, with ancient whole-genome duplication (WGD) events affecting several orders. Yet, genomes remain unavailable for a number of poorly studied orders, such as Opiliones (daddy-long-legs), which has hindered comparative study. We assembled the first harvestman draft genome for the species Phalangium opilio , which bears elongate, prehensile appendages, made possible by numerous distal articles called tarsomeres. Here, we show that the genome of P. opilio exhibits a single Hox cluster and no evidence of WGD. To investigate the developmental genetic basis for the quintessential trait of this group—the elongate legs—we interrogated the function of the Hox genes Deformed ( Dfd ) and Sex combs reduced ( Scr ), and a homologue of Epidermal growth factor receptor ( Egfr ). Knockdown of Dfd incurred homeotic transformation of two pairs of legs into pedipalps, with dramatic shortening of leg segments in the longest leg pair, whereas homeosis in L3 is only achieved upon double Dfd + Scr knockdown. Knockdown of Egfr incurred shortened appendages and the loss of tarsomeres. The similarity of Egfr loss-of-function phenotypic spectra in insects and this arachnid suggest that repeated cooption of EGFR signalling underlies the independent gains of supernumerary tarsomeres across the arthropod tree of life. 
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