Socially plastic responses in females are robust to evolutionary manipulations of adult sex ratio and adult nutrition

Abstract

AbstractBackgroundSocially plastic behaviours are widespread among animals and can have a significant impact on fitness. Here we investigated whether the socially plastic responses of femaleDrosophila melanogastercan evolve in predictable ways following long term manipulation of adult sex ratio and adult nutrient availability. Previous reports show that femaleD. melanogasterrespond plastically to their immediate same-sex social environment by altering their fecundity, laying fewer eggs after they mate if previously exposed to other females, Fecundity is also highly sensitive to a female’s immediate nutritional status, being significantly reduced when dietary protein in particular is scarce. On this basis, we predicted that an evolutionary history of exposure to variation in adult sex ratio and adult nutritional environment would select strongly upon a female’s plastic fecundity responses.ResultsWe used females that had been drawn from replicated lines that had experienced an evolutionary history of male biased, female biased or equal adult sex ratios and either standard or low-quality adult nutrition. We tested the specific predictions that a history of elevated competition among females (in female-biased regimes) would select for increasingly sensitive plastic fecundity responses to the presence of conspecifics, and that these would be magnified under poor nutritional resource regimes. In contrast to the expectations, we found that the plastic responses in females were strikingly robust to perturbations of both sexual competition and nutrient availability and did not differ significantly across any of the evolutionary regimes. The lack of response is not explained by an insufficient strength of selection. For example, among females held in isolation prior to mating, we did observe significant evolutionary responses in virgin egg according to nutritional regime and in virgin egg retention to sex ratio regime.ConclusionThe lack of variation in the existence and magnitude of predicted plasticity is consistent with the idea that the costs of maintaining fecundity plasticity in females are low, benefits high, and that plasticity itself can be hard wired.