American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Sex-specific among-individual covariation in locomotor activity and resting metabolic rate in Drosophila melanogaster

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Mathieu Videlier, Howard D. Rundle, and Vincent Careau (Dec 2019)

Read the Article (Just Accepted)

Sex differences in the metabolism-activity link imply males and females manage their energy budgets differently

<i>Drosophila melanogaster</i> in activity chambers. <br />(Credit: Vincent Careau)
Drosophila melanogaster in activity chambers.
(Credit: Vincent Careau)

According to a new study by a research team at the University of Ottawa, there are strong differences in how male vs. female flies manage their energy expenditures. Individuals expend energy (calories) for all bodily functions, from movement to breathing to digestion and reproduction. Two important components of the energy budget are those spent on bodily maintenance and activity, because both are fundamental to surviving and reproducing. How the two components co-vary among individuals is unclear, however. In their paper appearing in The American Naturalist, a team led by PhD student Mathieu Videlier gathered repeated measurements of maintenance energy expenditure and activity on several hundred Drosophila melanogaster. Surprisingly, the relationship between maintenance energy expenditure and activity was fundamentally different in males vs. females. In males, there was a strong and positive correlation between these, such that the individuals that spent more energy on maintenance were also more active. In contrast, the relationship was negative in females, such that the individuals that spent more energy on maintenance were also less active. These differences in the relationship between maintenance energy expenditure and activity between the sexes imply that male and female flies manage their energy budget very differently, perhaps arising from the different life histories of the sexes.


Abstract

A key endeavor in evolutionary physiology is to identify sources of among- and within-individual variation in resting metabolic rate (RMR). Although males and females often differ in whole-organism RMR due to sexual size dimorphism, sex differences in RMR sometimes persist after conditioning on body mass, suggesting phenotypic differences between males and females in energy-expensive activities contributing to RMR. One potential difference is locomotor activity, yet its relationship with RMR is unclear and different energy budget models predict different associations. We quantified locomotor activity (walking) over 24h and RMR (overnight) on 232 males and 245 females Drosophila melanogaster that were either mated or maintained as virgins between two sets of measurements. Accounting for body mass, sex, and reproductive status, RMR and activity were significantly and moderately repeatable (RMR: R=0.33±0.06; activity: R=0.58±0.03). RMR and activity were positively correlated among (rind=0.26±0.09) but not within (re=0.05±0.06) individuals. Moreover, activity varied throughout the day and between the sexes. Partitioning our analysis by sex and activity by time of day revealed that all among-individual correlations were positive and significant in males, but non-significant or even significantly negative in females. Such differences in the RMR-activity covariance suggests fundamental differences in how the sexes manage their energy budget.