Insights into Desiccation Resistance and Related Traits in Drosophila Melanogaster: Sex-specific Genetic Architecture and Selection

Abstract

Desiccation resistance is a key determinant of insect survival in terrestrial environments. While desiccation resistance often differs between the sexes, its sex-specific quantitative genetic architecture remains incompletely understood. Prior work, either explicitly or as a function of experimental design, tend to focus on females, and quantitative genetic studies, using individual-based measures, are rare. Using a pedigreed population of Drosophila melanogaster, I took many individual measurements of desiccation resistance (survival under extreme desiccation stress) alongside three traits that may underlie variation in this – metabolic rate, locomotory activity, and dry body mass. This allowed sex-specific additive genetic (co)variances for these traits to be estimated using quantitative genetic animal models, as well as phenotypic selection gradients. All traits were heritable in both sexes, with evidence for sex differences in additive genetic variance and covariance structure. Genetic correlations among traits differed in magnitude and sometimes in sign between males and females, but the uncertainty around individual estimates were too large to infer statistical significance. Cross-sex within-trait genetic correlations were generally close to one, except for locomotor activity, suggesting some potential for independent evolutionary responses in males and females. Using survival time under desiccation as a proxy for fitness, I found pronounced sex differences in viability selection. Selection differed significantly between the sexes overall, driven primarily by differences in selection on metabolic rate and body mass. In both sexes, survival under desiccation stress was associated with lower activity and larger body mass. In males, survival under desiccation was also associated with lower metabolic rate, while there was no evidence of selection on metabolic rate in females. Correlational selection also differed between sexes, with males exhibiting a more complex fitness surface. These results show that desiccation resistance is a multivariate trait shaped by sex-specific genetic architecture and sex-specific selection, emphasizing the importance of incorporating sex and individual-level variation when studying desiccation resistance and its evolution.