Evolution in heterogeneous environments: genetic variability within and across different grains in Tribolium castaneum.

The course of adaptation to heterogeneous environments is influenced by the magnitude of genetic variation for ecologically important characters within each environment and the extent of genotype x environment interaction. Using the genetic correlation between the expression of characters in different environments as a measure of genotype x environment interaction is particularly useful for evolutionary interpretation. In this study, we estimated patterns of genetic variability and cross-environment genetic correlations for pupal weight and development time in two strains of the flour beetle Tribolium castaneum in five flours (wheat with brewer's yeast, wheat, rice, corn and oat). Wheat plus yeast is the standard medium in which the strains have been reared for hundreds of generations; other flours are novel environments. The results indicated moderate levels of genetic variation within the various flours for pupal weight but not for development time. Performance varied considerably across flours, with the highest performance for both strains found in the standard medium and the poorest in oat flour. The genetic correlations of pupal weight across flours in both strains were generally not significantly different from + 1. This suggests that evolution of body size in different flours cannot proceed independently, and that improved performance in the novel flours may produce declines in fitness in the standard environment.