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

Abstract

Opiliones are iconic arachnids with a Paleozoic origin and a diversity that reflects ancient biogeographical patterns dating back at least to the times of Pangea. Due to interest in harvestman diversity, evolution and biogeography, their relationships have been thoroughly studied using morphology and PCR-based Sanger approaches to systematics. 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 analyze a set of the 14 existing transcriptomes with 40 additional ones generated for this study, representing ca. 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 are precisely placed. Our dating analyses also 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 a general overview of the general biogeographic patterns of this ancient arthropod group.