Comparative ecology and phylogeography in east African cichild fishes

Since almost two decades speciation outbursts, so-called adaptive radiations, have been put forward as a major reason for a large portion of the bio-diversity we see today. Adaptive radiations are indisputably very complex processes with many factors to consider. They are, however, not separable from the concept of ecological speciation by the means of natural selection. Hence the concept of convergent evolution, which states that different organisms independently evolve similar morphological or behavioral traits as a result of similar ecological selection regimes, was put forward as an essential indicator of the ‘adaptiveness’ of respective species differences and/or similarities. In the exceptionally species rich and eco-morphologically highly diverse assemblages of the East African Rift lakes, the paradox was put forward that competitive ecological exclusion of converging species seems to require a temporal and special separation (allopatry) of the different lineages in order for them to coexist. Recent phylogenetic framework and molecular dating seem to indicate though that in fact many lineages formed very rapidly thus not allowing the avoidance of competitive exclusion.
These are questions addressed in the first part of my thesis (“Comparative ecology”) consisting of two Chapters. 1: “Convergent evolution within an adaptive radiation of cichlid fishes” where we investigated ecologically based convergence within the Lake Tanganyika cichlid radiation and 2. “The ecological and genetic basis of convergent thick-lipped phenotypes in cichlid fishes” where we investigated the convergent occurrence of a conspicuous trait which is thought to be highly adaptive, the thick lipped phenotype of cichlid fishes.
Considering the strong connectivity of convergent evolution with the ecological properties of a habitat mediated by natural selection it is apparently crucial to study ecological parameters of habitats connected by convergent phenotypes which we did in Chapter 3: "Depth-dependent abundance of Midas Cichlid fish (Amphilophus spp.) in two Nicaraguan crater lakes". Here we characterised effective population sizes by means of transect methods in order to compare two lakes exhibiting convergent phenotypes.
In a second part (“Phylogeography”) I combine different studies dealing with a combination of distributional patterns, patterns of phylogenetic relationships and ecological factors of east African riverine cichlids since they have become increasingly important in the understanding of large-scale relations of African cichlid fishes. In Chapter 4: “Back to Tanganyika: a case of a recent immigration into a species flock of East African cichlid fishes” we investigate a recently discovered dispersal event of a modern cichlid lineage (Haplochromis spp.) across major watershed barriers in Eastern Africa. In Chapter 5: “Divergence between lake and stream habitats in an East African cichlid fish” we investigate the degree of ecological divergence of a riverine cichlid species, which also occurs in pure lake habitats (Astatotilapia burtoni). In Chapter 6: “Admixture between divergent mitochondrial lineages and greater phenotypic variation in a basal haplochromine cichlid fish from Lake Chila, Zambia” we investigate the phylogeographic history of a basal haplochormine clade (genus: Pseudocrenilabrus).
Morphological diversity within natural populations is a crucial prerequisite for natural selection to act on and to enable ecological adaptive evolution. A special case of such morphological variation, the mouth asymmetry of scale eating cichlid fish of Lake Tanganyika, was the main topic of the third part of my thesis (“Asymmetrical Polymorphism”) and Chapter 7: “A field based assessment of attack strategies and feeding success in the scale eating cichlid fish Perissodus microlepis (Perciformes)”.