Quantitative genetic variation for thermal performance curves within and among natural populations of Drosophila...

Thermal performance curves (TPCs) provide a powerful framework for studying the evolution of continuous reaction norms and for testing hypotheses of thermal adaptation. Although featured heavily in comparative studies, the framework has been comparatively underutilized for quantitative genetic tests of thermal adaptation. We assayed the distribution of genetic (co)variance for TPC (locomotor activity) within and among three natural populations of Drosophila serrata and performed replicated tests of two hypotheses of thermal adaptation--that 'hotter is better' and that a generalist-specialist trade-off underpins the evolution of thermal sensitivity. We detected significant genetic variance within, and divergence among, populations. The 'hotter is better' hypothesis was not supported as the genetic correlations between optimal temperature (T(opt)) and maximum performance (z(max)) were consistently negative. A pattern of variation consistent with a generalist-specialist trade-off was detected within populations and divergence among populations indicated that performance curves were narrower and had higher optimal temperatures in the warmer, but less variable tropical population.