Sex-specific genetic matrix (Gfm) and its between-sex genetic matrix (B): From evolutionary physiology in flies to empirical evidence and simulations on the B matrix asymmetry

Event Details

November 6, 2023
12:00 pm
RW432 and Livestream


Guest speaker: Mathieu Videlier, Postdoc – Sztepanacz lab
Host: J. Sztepanacz


Sexual dimorphism is widespread throughout the animal kingdom. One of the classic evolutionary scenarios for the emergence of sexual dimorphism is the presence of antagonistic selection between females and males, due to distinct phenotypic and fitness optimum. While this opposite selection between sexes can produce distinct distribution of traits between sexes, the genetic architecture underlying traits may act as a constraint and limit the sexual dimorphism evolution, leading to intralocus sexual conflict. To better understand this genetic limitation, researchers have focused their attention on the sex-specific genetic matrix (Gfm) to highlight distinct genetic (co)variances among traits within each sex (Gf and Gm), as well as the genetic covariances between sexes and traits residing in the between-sex genetic matrix (B).  

To better understand the emergence and evolution of sexual dimorphism, I decided to investigate the genetic constraints between sexes residing within the Gfm and more specifically in the B matrix in animal physiology (body mass, standard metabolic rate (SMR) and energetic demanding behavior as daily locomotor activity), under the assumption that sex specific fitness optimums should be supported by distinct energetic demands and budgets between sexes. I addressed this question in a Drosophila melanogaster laboratory population using paternal half-sib breeding design as well as a state-of-art high flow-through respirometry system. There were detectable additive genetic variances for all traits in both sexes, suggesting that physiological traits were heritable. Sexual differences in Gfm were largely driven by difference in genetic variance in locomotor activity between sexes. Overall, genetic variance was mostly shared between sexes with positive cross-sex genetic correlations within the B matrix, suggesting the existence of genetic constraints between sexes in physiological traits. Interestingly, the B matrix asymmetry was not significant due to a lack of power, but point estimates suggested that cross-sex cross-traits genetic correlations might differ within the B matrix.

This result led me to further investigate how the B matrix asymmetry affects the response to selection and emergence of sexual dimorphism. Surprisingly, while the cross-sex genetic correlations are often studied for a single or multiple traits, the B asymmetry is rarely explored, mainly due to the large uncertainty surrounding the cross-sex cross-traits genetic correlations. By compiling various Gfm and B matrices available from the literature, I decide to investigate whether the B asymmetry affects the response to selection, and in which sex the effect of Basymmetry is more predominant. 

Using simulation of different evolutionary scenarios (concordance and antagonistic directional selection between sexes), as well as different metrics to assess effect on evolution (L ratio or angle between response to selection with and without asymmetry), I found that the B asymmetry plays a role in altering the response to selection, with a tendency to affect females more than males in the case of antagonistic selection. These preliminary results can lead to a better understanding of the genetic constraint due to the B matrix that limits the evolution of sexual dimorphism.