Is variation in female aggressiveness across Drosophila species associated with reproductive potential?

Aggression is a key determinant of fitness in many species, mediating access to mates, food, and breeding sites. Variation in intrasexual aggression across species is likely driven by variation in resource availability and distribution. To date, most studies have focused on male aggression, but female aggression is common and has fitness consequences. While males primarily compete over access to mates, females are likely to compete over resources to maximize offspring quantity and/or quality, such as food or breeding sites. To investigate why reproduction and aggression are often linked, we tested predictions about resource valuation, life-history, and physiological correlates of reproduction. We used machine learning classifiers developed for D. melanogaster to identify and quantify aggressive behaviors displayed in the presence of yeast for mated and unmated females of eight Drosophila species. We found that female aggression was linked to ovariole number across species, suggesting that females that lay more eggs are more aggressive. A need for resources for egg production or oviposition sites or similar physiological mechanisms regulating aggression and reproduction may therefore be drivers of female aggression.