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Microevolution and development of a sexual dimorphic pigment pattern in cichlid fishes

Supervisor: Dr Emília Santos

Project summary:

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.

What the student will be doing:

In this project, the student will study eggspot number variation within a cichlid fish population - Astatotilapia calliptera from Lake Massoko, Tanzania - to understand what genes, cells and developmental mechanisms generate variation.

In an ongoing genome wide association study, we have recently identified several candidate regions associated with eggspot number variation in this population, including a 9kb genomic region harbouring one gene that is implicated in melanophore development. The student would follow up on this study to characterize: a) What are the causal mutations and pigment cells underlying variation? b) How does gene function control eggspot number development? c) What are the mechanisms generating variation in other cichlid species? Is it the same genetic and cellular mechanism?

The student will use gene expression techniques, such as in situ hybridization and qPCR, microscopy tools to visualize pigmentation development, as well as gene sequence and gene function analysis using Crispr/cas9. These laboratory experiments would be combined with fieldwork to collect samples from other cichlid species to test if the genes underlying variation in eggspot number are the same across the cichlid phylogeny.

References:

Eggspots: Santos ME, et al. Nature Communications 2014

Astatotilapia calliptera from Massoko lake: Malinsky M, et al. Science 2015

Crispr/cas9 in cichlids: Juntti SA, et al. Current Biology 2016

Funding:

Available for research costs.