Sex‐specific selection under environmental stress in seed beetles

Abstract

Sexual selection can increase rates of adaptation by imposing strong selection in males, thereby allowing efficient purging of the mutation load on population fitness at a low demographic cost. Indeed, sexual selection tends to be male-biased throughout the animal kingdom, but little empirical work has explored the ecological sensitivity of this sex difference. In this study, we generated theoretical predictions of sex-specific strengths of selection, environmental sensitivities and genotype-by-environment interactions and tested them in seed beetles by manipulating either larval host plant or rearing temperature. Using fourteen isofemale lines, we measured sex-specific reductions in fitness components, genotype-by-environment interactions and the strength of selection (variance in fitness) in the juvenile and adult stage. As predicted, variance in fitness increased with stress, was consistently greater in males than females for adult reproductive success (implying strong sexual selection), but was similar in the sexes in terms of juvenile survival across all levels of stress. Although genetic variance in fitness increased in magnitude under severe stress, heritability decreased and particularly so in males. Moreover, genotype-by-environment interactions for fitness were common but specific to the type of stress, sex and life stage, suggesting that new environments may change the relative alignment and strength of selection in males and females. Our study thus exemplifies how environmental stress can influence the relative forces of natural and sexual selection, as well as concomitant changes in genetic variance in fitness, which are predicted to have consequences for rates of adaptation in sexual populations.

Dietary stress increases the total opportunity for sexual selection and modifies selection on condition‐dependent traits

“…Our findings that several pre‐ and postcopulatory sexually selected traits exhibit marked reductions in mean trait expression following diet restriction accord with a number of previous studies on guppies (Devigili et al ; Gasparini et al ) and other species (David et al ; Cotton et al ; Fox et al ). Numerous studies have reported that individuals whose condition is experimentally manipulated exhibit reduced mean trait expression and reproductive success, leading to an overall increase in the opportunity for sexual selection (Zikovitz & Agrawal ; Martinossi‐Allibert et al ). However, when the whole population experiences a reduction in the resources available for reproduction, whether the opportunity for selection increases will largely depend on the effect of resources on the variance in the expression of sexually selected traits, rather than on their mean (Arbuthnott & Whitlock ; Fox et al ).…”

The consequences of sexual selection in well-adapted and maladapted populations of bean beetles†

“…; Martinossi‐Allibert et al. ). Sterilized females are able to compete with the focal females over egg laying substrate (i.e., seeds) and potential mating opportunities (personal observations).…”

The ecology of sexual conflict: Temperature variation in the social environment can drastically modulate male harm to females

“…Sexual conflict unfolds via two fundamentally distinct processes: intra‐locus sexual conflict (IASC), when the trait/s under sexually antagonistic selection share the same underlying loci (e.g., different optima for the same trait in males and females), or inter‐locus sexual conflict (IRSC), when sexually antagonistic selection targets different loci in both sexes (e.g., male adaptations involving one trait and female counter‐adaptations involving a different trait). Recent work has emphasized that both IASC and IRSC must be understood in its ecological setting (Gomez‐Llano, Bensch, & Svensson, ; De Lisle, Goedert, Reedy, & Svensson, ; Martinossi‐Allibert, Arnqvist, & Berger, ; Perry, Garroway, & Rowe, ; Perry & Rowe, ). On the one hand, several studies over the last few years have shown that IASC can be strongly modulated by the environment so that inter‐sexual correlations in fitness can change significantly across environments (Berger et al, ; Long, Agrawal, & Rowe, ; Punzalan, Delcourt, & Rundle, , but see Delcourt, Blows, & Rundle, ; Martinossi‐Allibert, Savkovic et al, ; Punzalan et al, ).…”