Female resource limitation does not make the opportunity for selection more female biased

Abstract

AbstractEnvironmental and physiological conditions affect how individual variation is expressed and translated into variance in fitness, the opportunity for natural selection. Competition for limiting resources can magnify variance in fitness and therefore selection, while abundance of resources should reduce it. But even in a common environment the strength of selection can be expected to differ across the sexes, as their fitness is often limited by different resources. Indeed most taxa show a greater opportunity for selection in males than in females, a bias often ascribed to intense competition among males for access to mating partners. This sex-bias could reverberate on many aspects of evolution, from speed of adaptation to genome evolution. It is unclear however, whether the sex-bias in opportunity for selection is robust to variations in environment or physiological condition that limit sex-specific resources. Here we test this in the model speciesC. maculatusby comparing female and male variance in relative fitness (opportunity for selection) under mate competition (i) with and without limitation of quality oviposition sites, and (ii) under delayed age at oviposition. Decreasing the abundance of the resource key to females or increasing their reproductive age was indeed challenging as shown by a reduction in mean fitness, however variance in fitness remained male-biased across the three treatments, with even an increased male-bias when females were limited by oviposition sites. This suggests that males remain the more variable sex independent of context, and that the opportunity for selection through males is indirectly affected by female-specific resource limitation.