Data from: Does sexual dimorphism reflect sexual antagonism? Covariation of female fitness with brothers’ sexual traits and their female homologues in neriid flies

Alleles favoured by sexual selection in males can reduce fitness when
expressed in females, resulting in intralocus sexual conflict. It remains
unclear whether such conflict is fully resolved by the evolution of sexual
dimorphism. If conflict persists, then female reproductive performance
might covary negatively with the expression of secondary sexual traits in
male relatives, and potentially with the expression of homologous traits
in females themselves. However, because secondary sexual traits often
exhibit strong condition dependence, a resource-poor developmental
environment could weaken the covariance between female fitness and the
expression of such traits. We tested these predictions using a split-brood
experiment in which neriid flies (Telostylinus angusticollis) were reared
on nutrient-rich or nutrient-poor larval diets, resulting in high (rich
diet) and low (poor diet) adult sexual dimorphism. Consistent with
predictions, in families reared on the rich larval diet, we found that
females whose brothers exhibited relatively large secondary sexual traits
produced fewer viable offspring. Moreover, rich-diet females with
relatively large homologues of male sexual traits exhibited increased
latency to oviposition. By contrast, in families reared on the poor larval
diet, we found no evidence of negative covariation between male secondary
sexual trait expression and female performance, and females with
relatively large male trait homologues exhibited reduced latency to
oviposition and increased fecundity. Our results confirm that sexually
dimorphic morphology can reflect sexually antagonistic fitness variation,
and suggest that intralocus sexual conflict remains unresolved in this
species. Our results also suggest that the nutritional environment can
modulate the signal of sexual antagonism.