Conclusions and final thoughts

Research on genotype-by-environment interactions (GEIs) and sexual selection is still in its infancy and while GEIs in this context have been studied in a few systems, it is far too early to know how general it is to find GEIs for sexual traits. More importantly, we have little empirical information on what the impacts of GEIs are for the operation of sexual selection. Do GEIs for sexually selected traits alter the relative fitness of genotypes across environments? Are female mating preferences also subject to GEIs, and how do GEIs influence the covariance between male trait and female preference? Theory shows that GEIs can greatly complicate the relatively simplistic scenarios envisaged by much of our current thinking about how sexual selection operates (Chapters 1-4). Sexual selection is about relative sexual competitiveness, and therefore, other individuals will always be important in determining this outcome. Nonetheless, sexual selection researchers have tended to think of male genetic quality as being fixed, so that a high quality male now, remains a high quality male over time and across environments. This is the essence of good genes sexual selection (Chapter 1). However, when GEIs exist, male genetic quality is dependent on the environment. While many examples exist in the sexual selection literature showing that male sexual trait expression, female preference, and even fitness can differ across environments (e.g., guppies across predator regimes) the field as a whole has not fully appreciated the consequences of GEIs for sexual selection (Chapter 1).