Adaptive radiations are characterised by the emergence of spectacular morphological diversity over short periods of evolutionary time. A notable example of this is the parallel radiations of haplochromine cichlids in the East African Great Lakes, which have evolved into hundreds of species, in some cases in less than a million years. These cichlids are famous for their diversity in colour, shape and craniofacial morphology, but have also extensively diversified in their sensory systems while adapting to specific niches. However, the evolutionary role of a key sensory modality, the mechanosensory lateral line system, is not known, despite its importance in mediating a range of fish behaviours vital for survival. In this thesis, a combination of comparative morphometric, genomics and behavioural studies are presented, aimed at unpicking the role of lateral line system diversification in cichlid speciation and adaptive radiation. Initially, the remarkable morphological diversity present among the Lake Malawi flock is described. Next, by focusing on ecomorphs within a small crater lake undergoing incipient ecological speciation, it is shown that this disparity is detectable early in population divergence. Following this, the results of research on two hybrid crosses of cichlid species with divergent lateral line system morphologies are presented, providing key insights into the genomic basis of morphological variation, and its significance in mediating collective behaviour. Finally, we quantify natural selection acting on genomic, morphological and ecological traits during undergoing initial population divergence of cichlids. A novel framework for measuring divergent selection on traits in such systems is proposed. Overall, the findings highlight key insights into the significance of this often-overlooked sensory modality for cichlid adaptive radiation. More broadly, these results enhance our understanding of the evolutionary processes that have generated the diversity of ecologically-relevant morphologies that we observe in cichlid radiations.
Ecomorphological diversification during adaptive radiation of East African cichlid fishes
Edgley, D. E. (Author). 9 May 2023
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)