1. ¹Aarhus Centre for Environmental Stress Research (ACES), Department of Ecology and Genetics, University of Aarhus, Ny Munkegade, Buildg. 540, DK-8000 Aarhus C, Denmark
2. ²Department of Ecology, Faculty of Biology, Sofia University, St Kliment Ochvidski 8, Dragan Tznkov, Sofia 1164, Bulgaria
3. ³School of Rural Science and Agriculture, University of New England, Armidale, NSW 2351, Australia

Correspondence: P Sarup, Aarhus Centre for Environmental Stress Research (ACES), Department of Ecology and Genetics, University of Aarhus, Ny Munkegade, Buildg. 540, DK-8000 Aarhus C, Denmark. E-mail: pernille.sarup@biology.au.dk

Received 20 July 2005; Accepted 6 March 2006; Published online 12 April 2006.

Abstract

Variation in 19 traits possibly relevant for thermal adaptation was studied in 11 populations of Drosophila buzzatii collected in southeast Australia. Using stepwise multiple regression, the variation was compared to variation in geographic coordinates and to a set of climatic variables estimated for each collection site. For 13 of the traits, a significant part of the variation was explained by climatic variables and/or geographic coordinates, suggesting directional selection for adaptation to the environment in the majority of traits studied. In 10 of the traits, both geographic coordinates and climatic variables explained significant proportions of the variation, with R² ranging from 0.075 to 0.58. Although larvae, pupae and adults of D. buzzatii share a common habitat, the measured traits were not correlated across life stages and gender. Also, there seemed to be special conditions in marginal populations near species borders, giving rise to nonlinear relations with latitude. Climate apparently does influence the adaptive evolution of the traits studied, but they also are affected by other factors that vary with latitude, longitude and distance to coast. These results highlight the complex challenges imposed by the environment on the adaptive process.