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

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.

Who will benefit from our research?

We will study a fundamental question of evolution and development of pigmentation patterns in a publicly popular model system - cichlid fishes. Our work will benefit academics studying evolution and developmental biology, academics studying pigmentation development and disease, and professionals working in conservation. Furthermore, due to the charismatic character, cichlids are a good model to promote evolutionary biology to the general public.

How will they benefit from our research?

Academic communication: To ensure a wide readership we aim to publish in broad subject journals with high impact factors. We will target open access journals or pay the premiums for open access. We will continue to attend international conferences and workshops in evolution, development and pigmentation fields to publicise our work through talks and posters. All resources and protocols generated will be freely available to the research community and stored in databases, such as NCBI or locally stored in the laboratory or personal web pages (e.g. https://cambridgecichlids.org/).

Public science communication: It is hard to communicate evolutionary concepts using the traditional model organisms, due to a lack of public interest in the organism itself. In this project we will use an already popular organism, the cichlid fish, as a model. We can therefore bypass one obstacle in effective scientific communication. First, cichlid fishes are very popular both as pets and zoo exhibits due to their beautiful and diverse pigmentation patterns, further understanding of the mechanisms generating their sheer diversity would capture the wider public imagination. Second, the diversity and the rich ecological knowledge about this group of species makes it easy to explain the process of evolution. Third, the project will show the importance of evolutionary research to a wider range of topics, such as how mutation can lead to either beneficial or detrimental phenotypes. This last point is important to capture wider public support for evolutionary biology research. We will communicate our research with schools and the general public. We will actively participate in outreach events, such as the Cambridge Science Week and Soapbox science events; we will use our departmental and personal websites to highlight our findings and University press officers to communicate with the press to disseminate our work in news format.

Cichlid conservation: Cichlids inhabit the East African Great Lakes that are delicate environments threatened by anthropomorphic action. The increase of fish farming, for example, led to the eutrophication of lake Victoria's waters, extinction of many species and change in colour patterns of some cichlid species. Understanding the mechanisms of colour pattern evolution will be useful to understanding how species adapt to changing environments. We will disseminate the importance of conservation in our outreach events and communicate our findings in the Cichlid Science meetings to reach the conservation community.

Health sector - biomedical research: The pigmentation trait studied derives from the neural crest cells, which are a very important cell population involved in crucial embryonic developmental processes in all vertebrates, including humans. Defects on the behaviour of these cells lead to many serious craniofacial and pigmentation defects (e.g. cleft palate and albinism). In a longer time-scale of the proposed research plan, the results from this project can have an impact in biomedical research of the genetic mutations that lead to such disease phenotypes. At this point we have a fundamental study that seems difficult to transfer to the health sector but we will continually review our data and its implications to biomedical research.