Individual condition mediates the costs of sexual conflict through both male harm and female resistance

Sexual conflict arises when the reproductive interests of males and females diverge, leading to decreased female fitness due to male-induced harm. Theory predicts that individuals in good condition invest more in costly traits associated with male harm and female resistance. Moreover, local adaptation should increase the costs of sexual conflict by improving individual condition. Here, I test these predictions by manipulating individual condition in males and females of the red flour beetle (Tribolium castaneum) and quantifying female fecundity under high and low sexual conflict. I show that the individual condition mediates the costs of sexual conflict, and this effect is driven by both condition-dependent male harm and female resistance. Furthermore, using populations selected in a poor-resource environment, I show that although female condition shows evidence of local adaptation, male condition does not, limiting the increase of the costs of sexual conflict. I propose that sex-differences in local adaptation, being faster in females than in males, are responsible for these results. Together, my findings demonstrate clear evidence of individual condition modulating the costs of sexual conflict due to its effect in both male harm and female resistance. Further research studying sex-differences in local adaptation and the mechanistic underpinnings of male harm and female resistance would be needed to better understand the evolution of condition-dependent sexual conflict.