Condition-dependent success of resource-based reproductive tactics across both sexes in Drosophila prolongata.

UNLABELLED: Because reproductive tactics vary in their energetic and fitness costs, individuals may increase their reproductive success by aligning their tactics with their physical condition. In resource-based mating systems, monopolizing valuable patches is energetically costly, yet potentially highly rewarding for males. In females, mating near resources may reduce the cost of mate search and assessment. However, the balance of costs and benefits associated with a given tactic may shift with an individual's condition. Here we studied this in the fruit fly Drosophila prolongata. In arenas containing resource-dense areas (RDAs) typically used as territories, we tracked the individual positions and behaviors of flies in groups using machine-learning-based pose estimation and behavioral classification. We found that large, high-condition males achieved elevated mating success through territoriality and courtship, whilst small males obtained copulations through high mobility, consistent with a scramble competition tactic. Female behavior was also condition dependent: large females spent more time in RDAs, mated sooner at those sites, and thus reinforced territory-based sexual selection, whereas small females mated later and more frequently outside RDAs, potentially avoiding harassment costs. In addition, we detected size-disassortative pairings, suggesting that the complex cost-benefit interactions encountered by females of varying condition can lead to counter-intuitive associations. However, given the limited duration of our observations and the high remating rate in this species, the prevalence of this disassortative mating pattern over longer time scales warrants further investigation. Our findings reveal how resource distribution and individual condition may interact to maintain multiple reproductive tactics in both sexes.

SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1007/s00265-026-03739-z.