Limited genetic variation for male mating success reveals low evolutionary potential for thermal plasticity in Drosophila melanogaster

Populations respond to novel environmental challenges either through genetic changes, through adaptive phenotypic plasticity for the traits in question, or by a combination of these factors. Here, we investigated the evolutionary potential of phenotypic plasticity for male mating success, locomotory ability, and heating rate (a physiological performance trait) in the fruitfly Drosophila melanogaster, using isogenic male lines from the Drosophila Reference Genome Panel (DGRP) and hemi-clonal males. We quantified thermal reaction norms of how male mating success changed in relation to a temperate gradient, ranging from cold (18 °C) via optimal (24 °C) to hot and stressful environments (either 30 °C or 36 °C). We found significant differences in male mating success and locomotory performance between different lines, as well as significant main effects of temperature, but no significant genotype-by-environment interactions (GEI:s). A statistical power analysis revealed that the variance explained by GEI:s for thermal plasticity using this sample size is likely to be modest or very small, and represent only 4% of the total variation in male mating success. The lack of strong GEI:s for these two behavioral traits contrast with the presence of significant GEI:s for male heating rate, as measured by thermal imaging (infrared camera technology). These results suggest that sexual selection through male mating success is not likely to be efficient in mediating evolutionary rescue through changed plasticity in response to changing temperatures.