The developmental environment modulates mating-induced aggression and fighting success in adult female Drosophila

Competition over access to resources early in life can influence development, and, in turn, affect competitive phenotypes in reproductive adults. Theory predicts that competition between adult females should be especially context‐dependent, because of constraints imposed by high costs of reproduction. However, the potential impact of developmental environments on competition in adult females remains little understood.
In Drosophila melanogaster, the developmental environment can strongly influence adult condition, and prime adult competitive behaviour. In this species, female–female aggression is dependent on reproductive state and increases after mating due to the receipt of sperm and seminal fluid components. However, the effects of the developmental environment on adult female aggression, and any potential interactions with mating status, are unknown.
To address this problem, we first raised flies at low and high larval density, which altered competition over limited resources, produced large and small adult females, respectively, and potentially primed them for differing levels of adult competition. We then fought the resulting adult females, either as virgins, or after receiving aggression‐stimulating ejaculates at mating, to test for interacting effects.
We found, as expected, that mating elevated contest duration. However, this mating‐induced boost in aggression was strongly exacerbated for high density (small) females. Low density (large) females won more contests overall, but were not more successful in fights after mating. In contrast, mating increased the fighting success in females raised in high density environments.
Our results suggest that individuals who experience competitive, resource‐limited, rearing conditions are more sensitive to the aggression‐stimulating effects of the male ejaculate. This finding highlights the importance of the developmental environment in mediating adult social interactions and provides support for the theory that female–female aggression should be highly context‐dependent.