Direct and correlated responses to artificial selection for high and low knockdown resistance to high temperature in Drosophila buzzatii

Knockdown resistance to high temperature (KRHT) is a genetically variable trait for thermal adaptation in insects. Selection for KRHT may affect a number of fitness components as well as resistance to several forms of environmental stress. To test for heritable (co)-variation in KRHT, we examined direct and correlated responses to bi-directional selection on this trait in Drosophila buzzatii. Replicated lines were artificially selected for decreased and increased KRHT. After 12 generations of artificial selection, lines diverged significantly for high KRHT only. Starvation resistance increased in two lines that strongly responded to selection for high KRHT, and these two lines also showed relatively longer chill-coma recovery time. Developmental time and body size showed no correlated responses to KRHT-selection. These results suggest that KRHT is a heritable trait that can evolve towards increased thermotolerance with no genetic trade-offs associated to starvation resistance, developmental time and body size.