Diversity, disparity and the temporal dynamics of eco-morphological adaptation in the cichlid radiation of Lake Tanganyika

Some fundamental questions on how species arise, adapt and persist, and what contributes to the dynamics and patterns of diversity, are still in the centre of attention of modern evolutionary research. In this PhD thesis I focus on the evolutionary phenomena called adaptive radiation as driving force of biodiversity, using cichlid fishes from the East African Great Lake Tanganyika. I characterise the diversity of this fish family in this lake and test theoretical predictions on how diversification is expected to proceed in adaptive radiations. Thereby, the primary focus in the main part of my thesis lays on morphological and ecological adaptation, as well as on evolutionary trade-offs.
By cataloguing the diversity of cichlid fishes in Lake Tanganyika and establishing an ichthyological collection I build the cornerstone for ongoing and future projects in the field of evolutionary biology, taxonomy, biodiversity research, as well as conservation biology around the cichlid fauna of Lake Tanganyika.
Based on this species inventory and the associated specimen collection I conducted an in-depth examination of the cichlid radiation in Lake Tanganyika using whole genome sequencing, detail quantification of morphological features in 2D and 3D (based on X-ray and computed tomography imaging), as well as molecular ecological information. On the basis of the virtually complete taxon sampling I could establish for the first time a correlation between ecology and several morphological traits across the entire cichlid radiation in Lake Tanganyika. This is in line with one of the major predictions on the outcome of an adaptive ration and suggests that the observed diversity in phenotypes reflect ecological specialisation via natural selection. Importantly, I show that the diversification of cichlid fishes in Lake Tanganyika was not a gradual process but rather followed consecutive pulses of morphological differentiation. This finding provides empirical support for two theoretical predictions of the adaptive radiation theory. Further I connect taxonomic richness to genetic diversity and gene flow within groups of closely related species. This provides interesting novel insights into speciation dynamics as a link between genetic diversity and speciation rate has long been suspected.
I also empirically test a newly established theoretical framework for an evolutionary trade-off between foraging morphology and parental care. With this I provide an alternative perspective on the diversity of trophic morphology in Lake Tanganyika cichlids – the too often neglected contribution of sexual dimorphism to diversity.
Taken together my work provides novel insights into patterns of eco-morphological adaptations in the Lake Tanganyika cichlid adaptive radiation and the underlying drivers of diversity and morphological disparity. And with adaptive radiation being a key process in generating novel biological diversity, this thesis contributes to the understanding of diversification dynamics which is critical in times of a global biodiversity decline.