The genetic and developmental basis of a novel pigment pattern in cichlid fishes

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In nature there is a huge diversity of species present. They vary in many attributes (traits), such as shape, size, colour, habitat, and behaviour. A central question of biology has always been: exactly what are the mechanisms that drive this variation between species? What are the units of inheritance (genes) that are important for this change? And what are the differences in early embryonic events that make this immense variety of species. The biggest limitation is that even the most closely related species are often still distantly related and separated by hundreds of thousands, if not millions, of years of evolution. Therefore close comparison between species can be difficult. One group of fish species, the cichlids, provide a unique opportunity to allow this study to happen. They mainly live in three African lakes (Malawi, Victoria and Tanganyika) and in each lake there are several thousands of very closely related species that show a huge range of diversity in shape, size, colour, habitat and behaviour. This provides a unique opportunity for looking at the evolution of morphologies between very closely related species. In this project we will focus on a specific pigmentation character - the colourful spots that are present in the anal fins of hundreds of cichlid species. The reason for this choice is that they originate from a group of cells called the pigment cells. These cells originate in early develop and then undergo change and migrate to the anal fin of the adult fish to form the egg-spot pattern present in the different species. Thus we are aiming to link what changes in embryonic development result in differences in pigmentation in the different fish species.We will do this in a number of ways: 1) We will compare development of egg-spots between species with different attributes to look for correlation with differences in egg-spot morphology; 2) We will make crosses between closely related fish species that have different egg-spots, and then look for genes that correlate with changes in attributes; 3) We will test for correlations between genes and different egg-spots in wild fish populations; 4) We will look at the action of genes (gene expression) during early development to identify which are important for the development of this trait; 5) Finally, we will remove or add any genes of interest in the fish genomes to test if they do in fact have a role in egg-spot formation.At the end of the project we hope to have identified how the variation between species in this important trait is generated. Since pigment cells are found in all vertebrates, our results will have larger implications for the group and will set us on the path towards a greater understanding of the mechanisms underlying vertebrate evolution and diversity.