The genetic and developmental bases of male genital organ size evolution

Male genital structures are among the most rapidly evolving morphological traits and are often the only features that can distinguish closely related species. D. simulans and D. mauritiana, for example, only diverged from their last common ancestor 240 thousand years ago, but are strikingly different in their external genital morphology. The claspers and posterior lobes, for example, are very different in both size and shape between these species. Both of these organs have important roles in copulation. Therefore, this process of rapid morphological evolution is thought to be driven by sexual selection and may reinforce the separation of species. However, little is known about the genetic basis for diversification of male genital organs. In order to unravel the genetic bases for clasper and posterior lobe size evolution, we performed high-resolution introgression mapping to resolve candidate regions previously predicted on the left arm of the third chromosome. Gene expression analysis and genetic manipulation of these regions has reduced the number of potential candidate genes, and revealed novel genes involved in genitalia development. Using these results, I propose a gene regulatory network underlying clasper development. The reciprocal hemizygosity test showed that tartan (trn), underlies clasper size evolution between these species. Trn is a Leucine Rich Repeat transmembrane protein, and is the first gene identified underlying genital organ size differences between species. Moreover, expression analysis of trn implies cis-regulatory evolution, and likely candidate trn enhancer has been identified. Therefore, this thesis provides insights into the cis-regulation of phenotypic divergence, and given that trn functions as a cell affinity molecule, this may represent a novel mechanism for the developmental regulation of organ size.

Grantor dc:publisher

Oxford Brookes University

Year dc:date

2019

Author dc:creator

• Hagen, Joanna Frances Donnelly

Contributors dc:contributor

• McGregor, Alistair

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/r0zb-6722

OAI identifier oai:identifier

tle:ef00eba2-ae6b-4261-a8b0-fa2f6df99828:d6bd9758-527a-46cd-bfe2-c433766e8fca:1