What are the genetic targets of sexual selection underlying rapid phenotypic divergence among species?

Background

Sexual selection can drive the rapid divergence of male secondary sexual traits, including bird plumage and the external genital structures of insects (Eberhard 2010). Identifying the genes and mutations that cause these differences is key to understanding the role of sexual selection as a driver of phenotypic diversity among species. However, the genetic basis of these differences is poorly understood (Hagen et al., 2019). The external male genital structures of flies are derived from legs and play important roles in copulation (Casares et al., 1997). For example the posterior lobes of the male genital arch intercalate between the female tergites and are important for species-specific recognition and copulation (Frazee and Masly, 2015). The posterior lobes of males of species of the Drosophila simulans clade (D. simulans, D. sechellia and D. mauritiana) have diverged dramatically in size and shape in less than 240,000 years, and are the only way to reliably distinguish these species morphologically (Garrigan et al., 2012; Kopp and True 2002). This difference is polygenic in basis but none of the causative genes have yet been identified (Zeng et al., 2000; Hagen et al., 2021). This project aims to identify and test genes underlying posterior lobe divergence through the following experimental objectives.

O1. Identify differentially expressed candidate genes underlying posterior lobe divergence between D. simulans, D. sechellia and D. mauritiana.

O2. Explore sequence variation of candidates within and among species.

O3. Test the function of candidates during posterior lobe development.

O4. Characterise the effects of variation in candidate genes on mating behaviour and reproductive isolation.

Methodology

O1 will compare RNA-seq data among the developing genitalia and legs of D. simulans, D. sechellia and D. mauritiana to identify genes that are differentially expressed in the genitalia but not legs that thus represent candidate genes contributing to differences in posterior lobe morphology among these three species.

O2 will use population genetics data to examine the levels of segregating and fixed sequence variants of candidate genes within and between the three species to help infer their contribution to posterior lobe divergence.

O3 will apply CRISPR/Cas9 genome editing to generate reciprocal hemizygotes to test the function of candidate genes and verify their contribution to posterior lobe divergence.

O4 will use behavioural tests to compare the effect of candidate gene reciprocal hemizygotes on different aspects of copulation and fitness. These experiments will be carried out at Oxford Brookes University supervised by Dr Daniela Nunes.Background

Sexual selection can drive the rapid divergence of male secondary sexual traits, including bird plumage and the external genital structures of insects (Eberhard 2010). Identifying the genes and mutations that cause these differences is key to understanding the role of sexual selection as a driver of phenotypic diversity among species. However, the genetic basis of these differences is poorly understood (Hagen et al., 2019). The external male genital structures of flies are derived from legs and play important roles in copulation (Casares et al., 1997). For example the posterior lobes of the male genital arch intercalate between the female tergites and are important for species-specific recognition and copulation (Frazee and Masly, 2015). The posterior lobes of males of species of the Drosophila simulans clade (D. simulans, D. sechellia and D. mauritiana) have diverged dramatically in size and shape in less than 240,000 years, and are the only way to reliably distinguish these species morphologically (Garrigan et al., 2012; Kopp and True 2002). This difference is polygenic in basis but none of the causative genes have yet been identified (Zeng et al., 2000; Hagen et al., 2021). This project aims to identify and test genes underlying posterior lobe divergence through the following experimental objectives.

O1. Identify differentially expressed candidate genes underlying posterior lobe divergence between D. simulans, D. sechellia and D. mauritiana.

O2. Explore sequence variation of candidates within and among species.

O3. Test the function of candidates during posterior lobe development.

O4. Characterise the effects of variation in candidate genes on mating behaviour and reproductive isolation.

Methodology

O1 will compare RNA-seq data among the developing genitalia and legs of D. simulans, D. sechellia and D. mauritiana to identify genes that are differentially expressed in the genitalia but not legs that thus represent candidate genes contributing to differences in posterior lobe morphology among these three species.

O2 will use population genetics data to examine the levels of segregating and fixed sequence variants of candidate genes within and between the three species to help infer their contribution to posterior lobe divergence.

O3 will apply CRISPR/Cas9 genome editing to generate reciprocal hemizygotes to test the function of candidate genes and verify their contribution to posterior lobe divergence.

O4 will use behavioural tests to compare the effect of candidate gene reciprocal hemizygotes on different aspects of copulation and fitness. These experiments will be carried out at Oxford Brookes University supervised by Dr Daniela Nunes.