Juli Mayorga Thesis Defense (Gonzalo Giribet, Advisor)

Title: Pseudoscorpion Systematics & Phylogenetics: Exploring the Effects of Accelerated Rates of Evolution on bothAncient and Recent Diversification

Abstract: Like many arthropod lineages, the arachnid order Pseudoscorpiones DE GEER, 1778 evolved long enough ago to be present for the coming together and breaking apart of the supercontinent Pangea, the rise and fall of the Dinosaurs, and many iterations of extreme global climatic fluctuations. Roughly 400 million years of diversification and extinction have resulted in 4,359 currently described extant pseudoscorpion species in 26 families, distributed across virtually all terrestrial habitats on Earth (except for the polar regions). Given their general ubiquity, these tiny animals (~2–8 mm) largely go unnoticed by humans, inhabiting cryptic microhabitats like the leaf litter layer and crevices underneath tree bark, rocks, and driftwood.

For a subset of arachnologists and general naturalists, however, pseudoscorpions have long been the subject of intrigue and careful study; captivating in their potential to shed light on the evolution of silk, venom, phoresy (hitchhiking), and the chelicerate body plan. The advent of molecular sequencing technologies has illuminated additional fascinating biological attributes about these animals, including abnormal mitochondrial tRNA and rRNA genes, accelerated rates of nucleotide substitutions relative to other arachnid orders, and evidence of a shared whole genome duplication event uniting pseudoscorpions with the arachnopulmonates. Despite 250 years of systematic attention, there is still a lot that we do not know about the evolutionary history of pseudoscorpions, including the basic phylogenetic backbones of many families and the implications of observed anomalies such as a whole genome duplication event.

Here I present a dissertation investigating the evolutionary history of the pseudoscorpion family Chthoniidae on three different scales. In Chapter 1, I perform the first target-enrichment phylogenomic analysis for the order, using ultraconserved elements (UCEs) to infer evolutionary relationships between chthoniid lineages and estimate divergence times using Bayesian inference and fossil calibrations. In Chapter 2, I zoom in on one subset of the chthoniid phylogeny, leveraging various forms of data extracted from UCE loci to test species delimitation hypotheses in Tyrannochthonius CHAMBERLIN, 1929 and Lagynochthonius BEIER, 1951 lineages on the Puerto Rican Island Shelf, and showing that as molecular delimitation analyses are discordant in this group, an integrated morphological and molecular taxonomic approach is the most appropriate. Finally, in Chapter 3, I zoom in even further into a single, synanthropic chthoniid species, Ephippiochthonius tetrachelatus (PREYSSLER, 1790), assemble the first chthoniid genome using PacBio HiFi long reads, and compare the general genome architecture and composition to the genome of the chernetid pseudoscorpion Cordylochernes scorpioides (LINNAEUS, 1778).

Committee:  Gonzalo Giribet (Advisor), Robin Hopkins, Brian Farrell, Mark Harvey