The independent adaptive radiations of cichlid fishes in the three Great East African Lakes, Victoria, Malawi and Tanganyika, holds a great potential for a comparative study. We will use the different ages of the 3 radiations to tackle the validity of the concept of genetic accommodation as a central mechanism of speciation and adaptive radiation. This evolutionary scenario posits that (1) a mutation or environmental change triggers the expression of novel, heritable, phenotypic variants within a population; (2) the initially rare variants start to spread (in the case of an environmentally induced change, due to the consistent recurrence of the environmental factor), creating eco-morphologically differentiated subpopulations expressing the novel trait; and (3) selection on existing genetic variation for the regulation or form of the trait causes it to become genetically fixed in individuals forming a new subpopulation. Such subpopulations ultimately evolve to new species adapted to alternative ecological niches. We plan to study the genomic basis of morphological differentiation of oral and pharyngeal jaws in three sets of convergent and eco-morphologically equivalent species with three different evolutionary ages, to elucidate the evolution of gene regulatory networks underlying the adaptive diversification of trophic morphology, and to study the relative importance of modification of gene regulatory processes versus de-novo mutations in coding regions with increasing divergence time. We selected 3 monophyletic sets of eco-morphologically equivalent model species: invertebrate and fry-predators, omnivorous species, algae grazers and algae browsers, as convergent equivalents in the littoral habitat of all 3 lakes. By combining comparative morphological analysis on the basis of microcomputer-tomography with next-generation sequencing approaches we intend to find genetic and gene regulatory correlates to divergent eco-morphologies. This will allow us to test whether the genetic architecture of eco-morphological divergence corresponds to the pattern predicted by the concept of genetic accommodation, or even the more specific scenario of the flexible stem hypothesis. To focus on evolutionary eco-morphological divergence in connection to speciation we plan to complement ongoing studies on the genetics of phenotypic plasticity in that we explicitly exclude effects of phenotypic plasticity on the development of particular head morphologies in our study design, by rearing all study species in a standardized (aquarium and food) environment. We aim to tackle the scenario of genetic accommodation at four levels: (1) non-coding RNAs, (2) the epigenetic regulation via CpG methylation, (3) gene expression, and (4) divergence in coding regions (protein evolution, gene duplications). To keep the research plan realistic for a grant period of 3 years, we will largely exclude the studies of downstream functional effects, and link the observed patterns to species- and ecotype-delimiting morphological features at two defined life stages, the stage of completed embryogenesis and onset of the adult stage.
|Effective start/end date||1/05/17 → 31/10/21|
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