Evolutionary trade-offs between thermal tolerance and locomotor and developmental performance in drosophilid flies

Cold-tolerant ectothermal animals are generally absent from warmer regions, suggesting that the acquisition of cold tolerance is associated with the loss of adaptation to warmer environments. In the present study, we compared thermal tolerance, walking speed (WS) and pupal development (PD) for 28 drosophilid species from cool-temperate, warm-temperate, and subtropical regions by the phylogenetically-based method and the conventional regression to understand trade-offs between these traits. A significant negative relationship was observed between cold tolerance and the rate of PD in both sexes and between cold tolerance and WS in the male in the phylogenetically-based analysis. Similar results were obtained in the conventional regression analysis, although the level of significance somewhat differed. Thus, cold tolerant species are assumed to have lost abilities to develop and walk fast. Subsequently, they may become more vulnerable to predators, parasitoids or infectious microorganisms and may have become extinct in warmer regions through enemy-mediated interactions and/or resource competition with cold susceptible species with faster development and quicker locomotion. In the present study, no significant relationship was observed between heat tolerance and WS or the rate of PD in the phylogenetically-based analysis, although heat tolerance was significantly related with the rate of PD in the conventional regression analysis. Thus, trade-offs associated with heat tolerance were not apparent.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 375–380.