Genetic variance of sexually selected traits in waxmoths: Maintenance by genotype x environment interaction

When traits experience directional selection, such as that imposed by sexua l selection, their genetic variance is expected to diminish. Nonetheless, t heory and findings from sexual selection predict and demonstrate that male traits favored by female choice retain substantial amounts of additive gene tic variance. We explored this dilemma through an ecological genetic approa ch and focused on the potential contributions of genotype X environment int eraction (GEI) to maintenance of additive generic variance for male signal characters in the lesser waxmoth, Achroia grisella (Lepidoptera: Pyralidae) . We artificially selected genetic variants for two male signal characters, signal rate (SR) and peak amplitude (PA), that influence female attraction and then examined the phenotypic plasticity of these variants (high- and l ow-SR and high- and low-PA lines) under a range of environmental conditions expected in natural populations. Our split-family breeding experiments indicated that two signal characters, SR and PA, and several developmental characters in both high- and low-SR a nd high- and low-PA lines displayed considerable phenotypic plasticity amon g the environments tested. Moreover, strong GEIs leading to crossover betwe en high- and low-SR lines were found for SR and developmental period. There fore, neither high- nor low-SR genetic variants would achieve maximum attra ctiveness and fitness in every environment, and those variants producing un attractive signals with low SRs under normal conditions may remain in popul ations provided that gene flow across environments or generation overlap ar e sufficiently high. We speculate that the phenotypic plasticity for SR and developmental period is adaptive in A. grisella populations experiencing a range of temperature and density conditions. Females mating with attractive (high-SR) males may be assured of obtaining good genes because these males sire offspring that develop more rapidly and a crossover for developmental period may parallel that for SR. Such parall el crossovers may be expected wherever good-genes sexual selection mechanis ms operate.