Basal cold but not heat tolerance constrains plasticity among Drosophila species (Diptera: Drosophilidae)
Thermal tolerance and its plasticity are important for understanding ectotherm responses to climate change. However, it is unclear whether plasticity is traded-off at the expense of basal thermal tolerance and whether plasticity is subject to phylogenetic constraints. Here, we investigated associations between basal thermal tolerance and acute plasticity thereof in laboratory-reared adult males of eighteen Drosophila species at low and high temperatures. We determined the high and low temperatures where 90% of flies are killed (ULT90 and LLT90, respectively) and also the magnitude of plasticity of acute thermal pretreatments (i.e. rapid cold- and heat-hardening) using a standardized, species-specific approach for the induction of hardening responses. Regression analyses of survival variation were conducted in ordinary and phylogenetically informed approaches. Low-temperature pretreatments significantly improved LLT90 in all species tested except for D. pseudoobscura, D. mojavensis and D. borealis. High-temperature pretreatment only significantly increased ULT90 in D. melanogaster, D. simulans, D. pseudoobscura and D. persimilis. LLT90 was negatively correlated with low-temperature plasticity even after phylogeny was accounted for. No correlations were found between ULT90 and LLT90 or between ULT90 and rapid heat-hardening (RHH) in ordinary regression approaches. However, after phylogenetic adjustment, there was a positive correlation between ULT90 and RHH. These results suggest a trade-off between basal low-temperature tolerance and acute low-temperature plasticity, but at high temperatures, increased basal tolerance was accompanied by increased plasticity. Furthermore, high- and low-temperature tolerances and their plasticity are clearly decoupled. These results are of broad significance to understanding how organisms respond to changes in habitat temperature and the degree to which they can adjust thermal sensitivity. © 2011 The Authors. Journal of Evolutionary Biology © 2011 European Society For Evolutionary Biology.