Experimental adaptation to larval malnutrition maintains male post-copulatory sexual success despite reduced investment in accessory glands.

We report the consequences of >330 generations of experimental evolution under larval undernutrition for male postcopulatory success and traits thought to mediate it in Drosophila melanogaster, comparing them to phenotypically plastic responses. Males from populations evolved on standard diet showed a >30% plastic reduction in the size of accessory glands (AG) when raised on a nutrient-poor larval diet. Experimental evolution on the poor diet led to a further reduction that was more pronounced in smaller individuals, changing the allometric slope between AG and wing size. Rather than the expected reduction in seminal fluid protein expression, we observed a plastic increase on poor diet in investment in Acp36DE and Acp62F at the expense of Acp26Aa and SP, and an evolutionary shift in the time course towards lower virgin and higher post-mating SFP expression. Surprisingly, neither the plastic nor evolved reduction in AG was associated with impaired performance in reproductive output from matings with excess females, the ability to induce female oviposition or performance in sperm competition ("sperm defense"), except when poor diet-adapted males were raised on standard diet. Thus, larval nutrient shortage favors reduced investment in AG development, but this is compensated for by other mechanisms, minimizing consequences for postcopulatory success.