Metabolic Rate in Drosophila: Sexual Dimorphism, Natural Selection, and Genetic Covariances with Mass and Locomotor Activity
Creators: name: Videlier, Mathieu
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2021
Subjects: Variance
Energetics
Evolution
Insect

description: A key endeavour in evolutionary physiology is to understand the causes and consequences of individual variation in metabolic rate, including its genetic basis and the selection that acts on it. In diecious species, males and females often differ in their reproductive strategies and this can generate sex-specific selection and the possibility of an evolutionary conflict between the sexes. Males and females may therefore manage their energy budgets differently to achieve these different goals, generating sex-specific selection on metabolic rate and the potential for intralocus sexual conflict. Little attention, however, has been given to the potential for such metabolic conflict. In my thesis, I addressed this by focusing on standard metabolic rate (SMR), the energy invested in the somatic maintenance, which constitutes a major component of an individual’s energy budget. Most studies on the evolution of metabolic rate have focused on endotherms likely because metabolic measurements are easier in larger animals. I took advantage of a high-throughput flow-through respirometry system that allows individual-level measurements of a large number of small insects, to study the SMR in the little insect Drosophila melanogaster. I used this system first to estimate the repeatability of the resting metabolic rate, RMR (SMR required individuals to be non-reproductive, but some individual were intentionally mated to quantify the effect of this), and to identify factors contributing to its among-individual variation including body mass, sex, and reproductive status. I also demonstrated that the among-individual phenotypic correlation between RMR and locomotor activity varied depending on time of the day and sex, suggesting fundamental difference in how males and female manage their energy budget. Second, I examined the covariance between SMR and relative fitness to estimate the phenotypic selection on SMR in males and females, and I developed some novel multivariate approaches to better account for trait-specific covariates compared to past methods. There was some evidence that selection differed between males and females, although this occurred in a portion of phenotypic space that was non-overlapping between the sexes. Strong collinearity between SMR and body mass also hampered the ability to separate selection gradient on these two traits despite substantial sample sizes. Third, I used a quantitative genetic breeding design to provide insight into the genetic architecture of SMR, body mass and general locomotor activity and how it differed between sexes. I detected additive genetic variances for those traits in both sexes with substantial difference between males and females in their genetic architecture. The genetic architecture also revealed that much of the genetic variance was shared among sexes with positive and strong cross-sex genetic correlations, indicating the potential for sexual conflict in this population. Overall, my results provide further support to the possibility of sex-specific energy management that may lead to an intralocus sexual conflict in this population. Quantifying sex-specific selection at the genetic level will be an important next step in this work.