Nonparallel Geographic Patterns for Tolerance to Cold and Desiccation in Drosophila-Melanogaster and Drosophila-Simulans

Abstract

D. melanogaster populations from the fluctuating temperate climate of Melbourne (38°S) and in the tropics at Townsville (19°S) were investigated for differentiation in cold tolerance and desiccation tolerance, and were found to differ as predicted a priori from climatic considerations. Flies from the former locality were more tolerant to both of these environmental stresses. In comparable D. simulans populations, there was no significant differentiation between populations for cold tolerance or desiccation tolerance. In both species, there was genetic variation within each population. It is hypothesised that the non-parallel patterns in these sibling species may be due to different genetic strategies in temporal variation for tolerance to the stresses associated with climatic extremes. For D. melanogaster and D. simulans, there was no strong association between cold tolerance and desiccation tolerance in either the Melbourne and Townsville populations. Correlations between the stresses over the 15 strains were calculated for the sexes, generations, localities and species separately and were all non-significant. Cold tolerance and desiccation tolerance thus involve different physiological mechanisms.