Investigating the functional effects of genes involved in genital divergence between Drosophila species

Despite being closely related in evolutionary time, species of the Drosophila melanogaster clade, D. simulans and D. mauritiana, show striking differences in the size and shape of male genital structures, including both the claspers and the posterior lobes. The claspers are key structures used during mating to grasp the female, enabling genital coupling and accurate sperm transfer. D. simulans males possess much smaller claspers with fewer sensory bristles compared to D. mauritiana males. In contrast, the posterior lobes, which also play a role in copulatory mechanics, are significantly larger in D. simulans than in D. mauritiana. To date, only two genes, tartan (trn) and sox21b, have been identified as contributing to size differences in male genital structures, with trn influencing clasper size divergence and sox21b contributing to divergence in posterior lobe size between D. simulans and D. mauritiana. Here, the wider cis-regulatory landscape of trn has been characterised in both genital and non-genital tissues to determine whether differences in genital morphology can be attributed to species-specific enhancer differences, and to explore the pleiotropic roles of the trn regulatory network. Tartan interacts with Tenascin-major (Ten-m) across tissues to facilitate organ differentiation. This study establishes the interplay of these genes in conferring clasper formation in the male genitalia. To assess the evolutionary pressures shaping genital divergence, mating experiments using reciprocal hemizygotes of trn and sox21b were conducted. It was found that males with only a functional copy of the D. mauritiana trn allele, that carry larger claspers with more sensory bristles, copulate for significantly less time than those with the functional D. simulans trn allele. Males with a functional D. mauritiana sox21b allele, that carry smaller posterior lobes, copulate for significantly less time than males with the functional D. simulans sox21b allele. This work provides new insights into how gene regulation and enhancer evolution drive the development and diversification of complex traits. By integrating functional genetics with evolutionary biology, this thesis advances our understanding of the processes governing morphological evolution and the role of sexual selection in shaping species-specific traits.

Grantor dc:publisher

Oxford Brookes University

Author dc:creator

• Hood, Emily Janet

Contributors dc:contributor

• Santos Nunes, Maria Daniela

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/y5c0-n954

OAI identifier oai:identifier

tle:fa48be01-782e-4de4-9032-bddba15da5d1:d6bd9758-527a-46cd-bfe2-c433766e8fca:1