Regressive Evolution of Vision and Speciation in the Subterranean Diving Beetles from Western Australia
Year: 2020
Type: dissertation
Abstract: Subterranean animals are highly specialized for life underground, having converged on regressive traits such as on loss of eyes/vision and pigmentation. Despite centuries of study, understanding the evolutionary processes and genetic basis for regressive characters is still the subject of considerable debate, with two main evolutionary drivers at the forefront: natural selection and neutral evolution. An assemblage of independently-evolved beetle species (Dytiscidae), from a subterranean archipelago in Western Australia, converged on eye/vision loss, providing a powerful system to explore the genetic basis of adaptive and regressive evolution in parallel. I conducted a behavioural light-dark study of six subterranean beetle species in the genera Paroster and Limbodessus, and revealed evidence for one light avoiding species. This study suggested that highly troglomorphic beetles may have evolved from an ancestor that exhibited negative phototaxis as a pre-adaptation to living in permanent darkness. To investigate whether genes specifically involved in vision showed patterns of neutral evolution, I carried out exon capture analyses on a suite of phototransduction genes, from a total of 36 beetle species (32 stygobionts and 4 surface beetles). I found evidence for pseudogenisation of six genes in multiple species, supporting the neutral theory. Finally, an 18 base pair deletion and a shared stop codon were found in the long wavelength opsin gene of a phylogenetic sister triplet of beetle species from one calcrete. I sequenced long wavelength opsin in other Paroster species and mapped the mutations to a robust multi-gene phylogeny, to show that the mutation was unique to these three sister species. These analyses provide strong evidence that the three species evolved underground from a common ancestor that was already adapted to living underground. My studies add to the growing body of evidence supporting the neutral theory as the mode of eye regression and the potential for speciation underground, and further highlight that subterranean dytiscids provide a unique model system for exploring fundamental questions on the evolution of subterranean animals.
Author: Barbara L. Langille
Language: English
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W3034385345