Adaptations to temperature in geographic races of the Queensland fruit fly Dacus (Strumenta) tryoni

Abstract

Four populations of Dacus tryoni collected from widely separated regions on the east coast of Australia (Cairns, Brisbane, Sydney, and East Gippsland) were compared in the laboratory to determine how they differed in their adaptations to temperature, and what adaptations have enabled the species to spread into colder areas. The main criteria used for the comparisons were the innate capacity for increase (rm) and its components : speed of development, survival rate, and fecundity. The races were compared at three different temperatures and in two successive years. Differences between the races from Cairns, Brisbane, and Sydney were often large and consistent, and in general they correlated well with differences in the climates of the respective geographic areas. At the lowest temperature the Sydney strain had the highest (rm), while the Cairns strain had the lowest. At the intermediate temperature there were no significant differences between the strains. At the highest temperature the Cairns strain had the highest (rm), while the Sydney strain had the lowest. The strain from East Gippsland behaved in an unpredictable way in most of the experiments, and rarely fitted into the trends set by the other three strains. The major differences appear to have been due primarily to adaptations affecting fecundity. There were also significant differences in the longevity of adults and the survival rates of immature stages, but not in speeds of development. The differences in fecundity may have been related to differences in the proportions of females fertilized in the experimental cages.