Genetic and developmental basis of pigment pattern evolution

Supervisor: Dr Emília Santos

We are interested in the genetic and developmental basis underlying morphological evolution using cichlid fishes as a model system. We study variation in sexually dimorphic pigmentation patterns that are important for male-male competition and female choice – eggspots. These are circular pigmentation markings present on the anal fins of approximately 1500 species of cichlid fishes. Eggspots are a highly variable trait, varying in colour, number and arrangement, both within and between species. They function as badges of status, being sexually selected via female choice in some species and via male-male competition in others.

Cichlids are one of the most species rich vertebrate families showing extreme diversity in their colour patterns. They are a fascinating system because despite the morphological diversity, they are genetically very similar, which allows for in depth comparative developmental studies between closely related species. Furthermore, the recent increase in genomic resources, the viability of hybrid crosses and to the application of the genome modification method - CRISPR/Cas9 makes them a highly attractive study system.

We use a combination of quantitative and population genomics, developmental genetics and fieldwork to address our questions.

References

Eggspots: Santos ME, et al. Nature Communications 2014; https://www.nature.com/articles/ncomms6149

Astatotilapia calliptera from Massoko lake: Malinsky M, et al. Science 2015; https://www.science.org/doi/10.1126/science.aac9927

Crispr/cas9 in cichlids: Clark B, et al. Royal Society Open Science 2022; https://royalsocietypublishing.org/doi/10.1098/rsos.220077

Egg-spot pigmentation pattern development: Clark B, et al. bioRxiv 2023; https://www.biorxiv.org/content/10.1101/2023.04.06.535385v1

Image: Astatotilapia calliptera “kisiba/masoko” male and female with associated anal fin pigment cell types.
Adult male (A) and adult female (B). Close up of an adult male anal fin (C) highlighting the egg-spot made up of highly packed xanthophore-like cells and iridophores. Iridophore are also sparsely distributed in other fin regions (blue arrows) (I,J) and other cell types present in the male anal fin such as melanophores (black arrow) and erythrophores (red arrow) (E,F). Adult female anal fin (D) highlighting cell types present throughout the fin, such as melanophores, and the two types of xanthophore-like cells, the one that contracts in response to epinephrine (orange arrow) and one other which is unresponsive to the treatment (yellow arrow) (G,H). The effect of epinephrine treatment to contract the pigment cells can be seen in (E-H). Scale bars are 1mm (C,D) and 0.25mm (E-J). Figure by PhD student Aaron Hickey.