A central question in evolutionary biology is how do new species evolve? Recent advances stem from studies of ecological speciation, where reproductive isolation among incipient species is promoted by divergent adaptation to local habitats. The cichlid fish Telmatochromis temporalis from Lake Tanganyika has evolved two ecologically distinct ecomorphs that occupy different habitats, with large bodied fish on rock habitat, and small bodied fish on shell-bed habitat. It has been suggested that the diversification of these two ecomorphs has taken place repeatedly and has been driven by ecological processes. In this thesis population genetic and phylogenetic analyses are presented of geographically-distinct populations. The results provide evidence for a repeatedly and independently-derived adaptation from rock to shell bed habitat, consistent with parallel evolution. Demographic expansions of most populations and splitting time estimates indicate that the age of habitat and hence habitat availability is vital in shaping population dynamics and evolutionary trajectories. A series of behavioural studies on wild caught fish demonstrated that body-size dependent competition is a fundamental mechanism that determines habitat use and mediates assortative mating in laboratory conditions. The extent of phenotypic plasticity in ecomorph-specific trait evolution was studied under controlled laboratory conditions on first generation offspring. The results suggest that absolute body size is subject to plasticity in both ecomorphs but size at sexual maturity is strongly heritable, with the shell ecomorph maturing at smaller body size. Overall these findings demonstrate how extrinsic factors and divergent selection continue to shape the evolution of novel phenotypes and genotypes in T. temporalis, despite ongoing genetic exchange between diverging lineages.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:633437 |
| Date | January 2013 |
| Creators | Winkelmann, Kai |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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