Diet quality impairs male and female reproductive performance and affects the opportunity for selection in an insect model

Environmental factors can have profound effects on the strength and
direction of selection and recent studies suggest that such
environment-dependent selection can be sex-specific. Sexual selection
theory predicts that male fitness is more condition dependent compared to
female fitness, suggesting that male fitness is more sensitive to
environmental stress. However, our knowledge about the effect of
environmental factors on sex-specific reproductive performance and on sex
differences in the opportunity for selection is still very limited. In the
present study, we investigated the sex-specific effects of diet quality
(yeast deprivation and flour type) in the red flour beetle Tribolium
castaneum. Specifically, we manipulated yeast supplementation in wheat and
whole-wheat flour in competition assays allowing to test for sex-specific
effects of food quality (i) on reproductive success and (ii) on the
opportunity for selection. Our data show that yeast deprivation in wheat
flour had significantly negative effects on body mass and reproductive
success of both sexes, while high quality flour (whole-wheat flour) was
able to buffer the negative impact to a large extent. Importantly, our
data suggest no sex-specific effect of dietary stress on reproductive
success because the magnitude of the negative effect of yeast deprivation
was similar for males and females. Moreover, our study demonstrates that
low food quality inflated the opportunity for selection and did not differ
between sexes neither under benign nor stressful dietary conditions. We
discuss the implications of our findings for the adaptation to stressful
environments.