The Opiliones Tree of Life: shedding light on harvestmen relationships through transcriptomics

Abstract

Opiliones are iconic arachnids with a Palaeozoic origin and a diversity that reflects ancient biogeographic patterns dating back at least to the times of Pangea. Owing to interest in harvestman diversity, evolution and biogeography, their relationships have been thoroughly studied using morphology and PCR-based Sanger approaches to infer their systematic relationships. More recently, two studies utilized transcriptomics-based phylogenomics to explore their basal relationships and diversification, but sampling was limiting for understanding deep evolutionary patterns, as they lacked good taxon representation at the family level. Here, we analysed a set of the 14 existing transcriptomes with 40 additional ones generated for this study, representing approximately 80% of the extant familial diversity in Opiliones. Our phylogenetic analyses, including a set of data matrices with different gene occupancy and evolutionary rates, and using a multitude of methods correcting for a diversity of factors affecting phylogenomic data matrices, provide a robust and stable Opiliones tree of life, where most families and higher taxa are precisely placed. Our dating analyses using alternative calibration points, methods and analytical parameters provide well-resolved old divergences, consistent with ancient regionalization in Pangea in some groups, and Pangean vicariance in others. The integration of state-of-the-art molecular techniques and analyses, together with the broadest taxonomic sampling to date presented in a phylogenomic study of harvestmen, provide new insights into harvestmen interrelationships, as well as an overview of the general biogeographic patterns of this ancient arthropod group.

A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error

“…On the other hand, the distribution of RCFV is used as a measure of the variability in composition, but it does not provide critical values. In practice, values of RCFV are used as relative guidelines to identify genes or partitions with greater or lower values of this index (Struck et al, 2014;Andrade et al, 2015;Struck et al, 2015;Whelan et al, 2015;Fernández et al, 2016Fernández et al, , 2017. In our datasets, the use of loci with low or high RCFV had no effect on the placement of horseshoe crabs (supplementary Figure S17), while those that failed χ 2 showed a few but obvious anomalous groupings: polyphyletic Solifugae, Pseudoscorpiones and the myriapod Glomeris pustulata as sister group to Xiphosura (supplementary Fig.…”

A well‐resolved transcriptomic phylogeny of the mite harvestman family Pettalidae (Arachnida, Opiliones, Cyphophthalmi) reveals signatures of Gondwanan vicariance

“…Information on sampling localities and accession numbers in the NCBI Sequence Read Archive (SRA) database for each transcriptome can be found in Table . In addition, three pettalids from a previously published study (Fernández et al, ) were included. The following taxa were used as outgroups: a horseshoe crab ( Limulus polyphemus ), a scorpion ( Centruroiudes sculpturatus ), a spider ( Liphistius malayanus ) and eight non‐pettalid harvestmen ( Synthetonychia glacialis , Acropsopilio neozealandiae , Forsteropsalis pureora , Siro boyerae , Miopsalis sp., Metasiro savannahensis , Brasilogovea microphaga and Metagovea oviformis ).…”

“…100 Ma from Burmese amber (Poinar, ), there are fossils of non‐cyphophthalmid Opiliones that date to the early Devonian ( ca . 411 Ma; Dunlop, Anderson, Kerp, & Hass, ), and previously published dated phylogenies of Opiliones suggest Cyphophthalmi may already have been diversifying in the Permian or Carboniferous (Fernández, Sharma, Tourinho, & Giribet, ; Oberski et al, ; Sharma & Giribet, ). Together, these characteristics (narrow habitat requirements, low vagility, old age predating Pangean and Gondwanan breakup) make mite harvestmen an excellent system for studying historical biogeography (e.g.…”

First fossil harvestmen (Arachnida: Opiliones) from Spain and notes on the fossil record of Opiliones

“…The suborder Eupnoi comprises two superfamilies, the monotypic Caddoidea and Phalangioidea, with four families (Kury, 2017;Fernández et al, 2017). Only two living families are found in the Western Palearctic Region.…”

“…Within Sclerosomatidae, four subfamilies are currently regarded: the Pantropical Gagrellinae, the Holarctic Leiobuninae, and the Palearctic Gyinae and Sclerosomatinae (Pinto-da-Rocha and Giribet, 2007). The Gyinae, lacking coxal denticle rows, must be transferred to the Phalangiidae, as shown by the molecular analyses of Hedin et al (2012) and Fernández et al (2017). Among the other three subfamilies, the Sclerosomatinae present sclerotized bodies with a tuberculate opisthosoma and short legs, so it can be excluded.…”