The genetic mechanisms that coordinate the development and morphological divergence of Drosophila genital structures

External male genitalia are one of the most rapidly evolving insect body parts. Although the developmental programmes required to form some of these structures are known to some extent, the genetic differences causing phenotypic divergence are not well understood. Drosophila simulans and D. mauritiana exhibit striking morphological differences in the size, shape, and bristle composition of the male periphallic genitalia, despite only diverging 240,000 years ago. In my PhD project, I first investigated the genetic components underlying male posterior lobe shape and size differences between D. simulans and D. mauritiana. By performing RNAi knockdown against differentially expressed transcription factor encoding genes, I identified Sox21b. I found that posterior lobe size is repressed by Sox21b during larval genital development. To investigate whether it had evolved between species, I conducted reciprocal hemizygosity tests and found that posterior lobe size and shape differences are causative of Sox21b evolution between D. simulans and D. mauritiana. I then isolated an enhancer driving Sox21b expression in the posterior lobe primordia, which is positively regulated by Abd-B. By comparing this enhancer’s activity between D. simulans and D. mauritiana I found differences consistent with Sox21b gene expression differences. In parallel, I aimed to better understand the developmental programme coordinating genital development. It has been shown that the genital structures are a derived walking appendage body part, yet gene regulatory network conservation between different developmental contexts is not well understood. I focused on the leg pretarsal gene regulatory network coordinated by the transcription factor C15, and its similarities and differences during male clasper and female epiproct genital development. I characterised the expression and function of C15 and its interacting genes in both structures and described network similarities and differences. I also found that during male clasper development, C15 uniquely represses bristle growth in contrast to its activator role elsewhere in the fly. I identified the enhancer coordinating C15 male genital expression and predicted upstream TFs that may regulate its male-genital specific expression. Overall, my study has contributed new insights into the causative genetic basis for the rapid evolution of male Drosophila genitalia and the gene regulatory networks underlying the development of these structures.

Grantor dc:publisher

Oxford Brookes University

Year dc:date

2023

Author dc:creator

• Ridgway, Amber Mae

Contributors dc:contributor

• McGregor, Alistair

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/340x-nt42

OAI identifier oai:identifier

tle:f07a3b73-ca87-48bb-a666-113d1128c21c:d6bd9758-527a-46cd-bfe2-c433766e8fca:1