Dissecting the phenotypic and functional consequences of sexual selection on sperm competition through a species-specific multigene family

Species-specific genes have been shown to impact crucial aspects of organismal fertility and viability, mediating adaptation to changing environments. Nevertheless, how these genes exert their effects - as opposed to ancient genes, i.e. those present in multiple species - is poorly understood. This project is focused on the functional characterization of a recently originated, tandemly duplicated gene named sperm-specific dynein intermediate chain (Sdic), which was previously shown to be important for male fertility.

This project will help train one postdoc, two graduate students, six undergraduates, and a large number of high-school students in functional and evolutionary analyses of genomes, with a particular focus on inclusion of members of underrepresented groups. All data and materials generated will be made publicly available to the scientific community.

Sperm competition is a key mechanism of sexual selection that biases reproductive output upon mating. Although multiple genes are likely to impact sperm competition, a much lower number is relevant in driving its evolution. The Sdic gene is unique to the species Drosophila melanogaster.

It is a defective form of another gene named sw, and it is present in multiple copies. Sdic has been shown to impact progeny number in cases with multiple sires of the same female, and the sequence shows signatures of positive selection. In this project, the effects of Sdic on sperm displacement will be analyzed using engineered versions of the Sdic region and fluorescence-based techniques to track the sperm in the female reproductive tract.

In addition, the patterns of expression differentiation among different Sdic copies across multiple biological samples will be scrutinized using RNA-seq, which will help reveal how at least some of the Sdic copies have become functionally specialized. Lastly, using proteomic approaches, the novel functional properties of the Sdic product in relation to sw will be uncovered.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.