Geography, genomics, and evolutionary success in an insular environment

Abstract

Oceanic archipelagos are considered to serve as ideal natural laboratories for the study of ecology, evolution and conservation, providing a suitable framework to improve our understanding of the drivers of speciation. Evolutionary radiation is considered one of the more recognisable features of oceanic islands and represents a phenomenon that has long intrigued evolutionary biologists. Studies focusing on species radiations have provided a rich source of new insights into the evolutionary process and the mechanisms underlying diversification. Insular diversification is frequently associated with ecological drivers, however, non-ecological mechanisms may also drive diversification and speciation within insular settings by promoting geographic isolation. Applying phylogenetic and population genomic approaches, the present thesis investigates the dynamics of speciation within a super-radiation of weevils on the Canary Islands. The main objective is to understand the relative implications of geological events, climatic dynamics, geography and topography on the dynamics of diversification between and within islands. From the mitochondrial data analysed, strong evidence was found supporting a role for mega-landslides as drivers of island colonisation. The nuclear genome phylogeny revealed that, with some minor exceptions, species from each island are consistent with a single founding event for each island based on patterns of nuclear relatedness. In contrast, mitochondrial genetic variation shows more complex relationships among islands, reflecting multiple founding events for each island. The species complex from Gran Canaria, a geologically inactive island with high topographic complexity, points to the role for the interaction of topography and climate dynamics as a driver of diversification, revealing a complex speciation history involving repeated episodes of population isolation and admixture. Within the geologically more active island of Tenerife, the L. tessellatus species complex revealed a dynamic of more recent isolation and secondary contact, with the geography of individual relatedness implicating a role for gravitational flank collapses. These findings suggest that geologically active islands produce changes in the populations dynamic which may have a positive effect on regional genetic variation over the long term. Overall, the findings from this thesis highlight the analytical power of next generation sequencing technologies to shed light into the fine-scale genomic understanding of evolutionary process.