Macro-evolution in brittle stars
AffiliationSchool of BioSciences
Document TypePhD thesis
Access StatusThis item is embargoed and will be available on 2021-01-31.
© 2018 Dr. Guadalupe Bribiesca Contreras
Conspicuous large-scale diversity patterns and the disparity of species-richness across different taxonomic groups have fascinated naturalists for centuries. In recent years, advances in molecular techniques have facilitated the generation of large amounts of genetic data and have permitted the investigation of long-standing macro-evolutionary questions in a phylogenetic framework, even when the fossil record is scant. With the deep-sea being largely unexplored, many questions remain unanswered and processes affecting diversity in the oceans are far less understood than in terrestrial or aquatic ecosystems. Brittle stars have become a great model to study evolutionary processes, as an extensive genomic dataset has been generated. In this thesis, I aimed to identify large-scale diversity patterns in the oceans and to investigate their underlying processes in a phylogenetic framework. I used this extensive dataset, global distributional records, and novel phylogenetic approaches to investigate major processes at global scales. I investigated the dynamics of bathome shifts and the role of the deep-sea in generating diversity. The findings of bathymetric ranges being highly conserved, and shifts being infrequent, served as a baseline for the other chapters where evolutionary processes were investigated within bathomes. I also investigated the effect of the emergence of biogeographic barriers in shaping diversity patterns of tropical, shallow-water brittle stars. The temporally and spatially concordant divergences of clades, concordant across families, evidenced the role of plate tectonics in shaping spatio temporal patterns of diversity. Similarly, the role of geological processes in the evolution of the fauna of southern Australia was investigated. Three major components have been identified for this fauna, which are the result of geological and historical processes. Recent colonisations, either from tropical species colonising higher latitudes or temperate taxa dispersed from other regions in the Southern Ocean, have been identified based on fossil evidence. However, although a Gondwanan component has been suggested, fossils from the late Cretaceous are scarce, limiting our knowledge about the effect of the break-up of Gondwana. Revisiting this question using one of the most complete metazoan phylogenies to date reaffirm the important role of the Antarctic Circumpolar Current (ACC) in shaping diversity patterns in the Southern Hemisphere, but also of the break-up of Gondwana. Lastly, I investigated colonisations of anchihaline environments. Although several marine taxa have cave-adapted lineages, only three brittle stars have been reported to occur in these environments. As, these species belong to different families, they must represent independent colonisation events. I used evidence from multiple loci to perform species delimitation using robust methods, and assessed models of origin of cave fauna in a phylogenetic framework, considering life-history traits, and demographic history for the cave population. The questions addressed in this thesis evidence the power of phylogenomic approaches that in combination with extensive distributional datasets, shed light into macro-evolutionary processes. The results presented herein contribute and advance our knowledge about diversity and evolutionary processes in our oceans, and provide a framework for future research.
Keywordsbiogeography; brittle stars; shallow-waters; macro-evolution; origin; southern Australia; anchihaline; species delimitation; deep-sea
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