An integrative approach to velvet worm biodiversity and systematics

Abstract

Understanding patterns of biodiversity in many invertebrate groups is challenging not only due to a lack of taxonomic resolution, but also due to a lack of molecular resources to effectively delimit species and robustly assess their relationships to one another. Here, I focus on the velvet worms (phylum Onychophora), an invertebrate group with longstanding and ongoing taxonomic challenges. Systematic work in this dispersal-limited terrestrial phylum has been difficult due to their limited morphological variation and unusual aspects of their DNA, such as their large genome size, GC content, and genetic variability. However, despite these challenges evidence has grown for a high number of cryptic species within the group. In 2023 the first high quality velvet worm genome was published, followed in 2024 by an ultra-conserved element (UCE) probe set designed to help resolve phylogenetic relationships in the phylum. These advances have now made it possible to conduct comprehensive explorations of species diversity and biogeography in this little-studied phylum. In this dissertation I focus on two genera with contrasting reproductive strategies from Australia and Aotearoa New Zealand, the oviparous Ooperipatellus, and the ovoviviparous Peripatoides. Using these genera as case studies I take an integrative and multileveled approach to the understanding of onychophoran biodiversity, combining DNA barcoding, targeted sequence capture, morphology, and ecological niche modeling to explore species diversity and distributions. In Chapter 1, I review historic taxonomic work and use DNA barcoding and single locus species delimitation approaches to generate updated estimates of species diversity for Ooperipatellus and Peripatoides in Aotearoa. In Chapter 2, I show for the first time the utility of UCEs and SNP-based species delimitation methods for determining species diversity in velvet worms, resulting in the description of three new species of Ooperipatellus from Tasmania, Australia. In Chapter 3, I use ecological niche modeling to explore how climate refugia and environmental change since the last glacial maximum have shaped the distributions of Ooperipatellus in both Australia and Aotearoa. I also identify six new putative species of Ooperipatellus in Aotearoa. Lastly, in Chapter 4, I use UCE data to explore the validity of described species in the genus Peripatoides, several of which are cryptic species with overlapping distributions. The results of my analyses reveal evidence of admixture and highlight how samples with mixed ancestry can complicate species delimitation attempts, especially when using approaches that assume discrete genetic structure.