The molecular basis of phenotypic plasticity and genetic assimilation in rapidly evolving lineages of East African cichlid fishes

点击翻译按钮获取中文摘要

An organisms ability to adjust its phenotype in response to environmental stimuli is termed phenotypic plasticity. Traditionally it is often seen to hamper and constrain evolution. However, this view is debated and alternatively the flexible-stem hypothesis of West-Eberhard suggest the opposite, that exactly phenotypic plasticity (and what she calls developmental recombination) facilitates in stem lineages of adaptive radiations their rapid evolution and speciation into many specialized and less plastic species that then make up adaptive radiations. Based on this hypothesis developmental plasticity is seen to lead evolutionary change that later, even in lack of the initial environmental stimulus, is phenotypically expressed in alternative phenotypes through genetic assimilation. Here, we set out test the predictions of the flexible-stem hypothesis (FSH) in a set of four carefully chosen representative cichlid fish species from the adaptive radiations of Lake Victoria and Lake Malawi and two riverine basal lineages. Cichlid fishes have undergone explosive adaptive radiations in several East African lakes, filling a vast array of ecological niches, and thus represent an ideal model in which to test this hypothesis. In previous work and in preliminary experiments we could induce in split-broods different types of teeth and pharyngeal jaw morphologies based on the hardness of the diets that was fed to the fish (hard snails vs. crushed snails). It was possible to produce drastically different feeding morphologies in one of the non-endemic riverine cichlids. In accordance with the FSH we expect that the reaction norms will be much smaller in both of the two pairs of specialized and derived species from the adaptive radiations of Lakes Victoria and Malawi. In previous RNA-seq experiments and later work we identified several sets of co-expressed genes that were active during different phases of the jaw transformation towards a durophagous (snail-crushing) jaw. We plan to do conduct feeding-experiments with all six species as well as RNA-seq analyses that will be analyzed and interpreted within a known phylogenetic framework. We anticipate that both the variation in morphology as well as in transcriptional will be smaller in the four derived and specialized endemic members of the adaptive radiations (that are of different ages) than in the two basal species as would be predicted by the FSH. Further bioinformatics analyses will investigate variation and changes in promoters of genes involved in the adaptive phenotypic response and compared with other sets of neutral genes.