Unravelling mate choice evolution through indirect genetic effects

Attractiveness is not solely determined by a single sexual trait but rather by a combination of traits. Because the response of the chooser is based on the combination of sexual traits in the courter, variation in the chooser’s responses that are attributable to the opposite-sex courter genotypes (i.e., the indirect genetic effects (IGEs) on chooser response) can reflect genetic variation in overall attractiveness. This genetic variation can be associated with the genetic basis of other traits in both the chooser and the courter. Investigating this complex genetic architecture, including IGEs, can enhance our understanding of the evolution of mate choice. In the present study on the field cricket Gryllus bimaculatus, we estimated (1) genetic variation in overall attractiveness and (2) genetic correlations between overall attractiveness and other pre- and post-copulatory traits (e.g., male latency to sing, female latency to mount, male guarding intensity, male and female body mass, male mandible size and testis size) within and between sexes. We revealed a genetic basis for attractiveness in both males and females. Furthermore, a genetic variance associated with female attractiveness was correlated with a genetic variance underlying larger male testes. Our findings imply that males that mate with attractive females can produce offspring that are successful in terms of pre-copulatory sexual selection (daughters who are attractive) and post-copulatory sexual selection (sons with an advantage in sperm competition), potentially leading to runaway sexual selection. Our study exemplifies how the incorporation of the IGE-framework provides novel insights into the evolution of mate choice.