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

Abstract

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. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13214/suppinfo is available for this article.

Keywords: Drosophila; early‐life effects; female–female competition; resources; seminal fluid; sex peptide; sexual selection; social selection.

Figure 1

Body mass and egg production. (a) Low density females were significantly heavier than females raised at high density. Sample sizes: HM = 59, HV = 66, LM = 66, LV = 57. (b) Low density females and mated females produced more eggs over 24 hr than high density and virgin females. Sample sizes (no. of females laying eggs): HM = 110, HV = 107, LM = 107, LV = 118

Figure 2

Feeding duration and attacks initiated by focal females. (a) Low density females initiate contests more than high density females, and all females attack more when their competitor is from high density. Competitor mating status is not shown as it was not significant in the model, while competitor larval density was. Sample sizes: HM vs. H: 28, HV vs. H: 18, LM vs. H: 27, LV vs. H: 35, HM vs. L: 35, HV vs. L: 28, LM vs. L: 18, LV vs. L: 33. (b) Mated females and high density females spent more time feeding, and females spent more time feeding when facing a high density competitor. Competitor mating status is not shown as it was not significant in the model, while competitor larval density was. Sample sizes: HM vs. H: 84, HV vs. H: 82, LM vs. H: 90, LV vs. H: 92, HM vs. L: 92, HV vs. L: 90, LM vs. L: 86, LV vs. L: 96

Figure 3

Proportion of encounters won by focal female treatment split by competitor female mating status and larval density treatment. Different shaded bars represent different focal treatments (i.e., combined mating status and larval density treatment). All combinations of focal and competitor are shown, so some treatments are the reciprocals of others; for example, high density mated focal vs. high density virgin competitor is the exact reciprocal of high density virgin focal vs. high density mated competitor. Sample sizes (no. of pairs of females): HMHM: 22, HVHM: 20, HVHV: 21, LMHM: 22, LMHV: 23, LMLM: 20, LVHM: 24, LVHV: 22, LVLM: 23, LVLV: 25

Figure 4

Contest duration by focal female treatment split by competitor female mating status and larval density treatment. Different shaded bars represent different focal treatments (i.e., combined mating status and larval density treatment). All combinations of focal and competitor are shown, so some treatments are the reciprocals of others; for example, high density mated focal versus high density virgin competitor is the exact reciprocal of high density virgin focal versus high density mated competitor. Sample sizes (no. of pairs of females): HMHM: 22, HVHM: 20, HVHV: 21, LMHM: 22, LMHV: 23, LMLM: 20, LVHM: 24, LVHV: 22, LVLM: 23, LVLV: 25