Reeve, Michael William; (2002) Temperature, Body Size and Life History in Drosophila melanogaster. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Body size in Drosophila melanogaster results from the combination of evolutionary genetic and developmental effects, both of which are affected by the thermal environment. Evolution or development at lower environmental temperatures results in increased body size in fruitflies, however, the reasons for these adaptations remain elusive. To investigate whether larger size is favoured at lower temperature through natural selection on adult males, life-span and age-specific-fertility of males from lines artificially selected for increased and decreased body size were examined at two different temperatures. Larger males were found to be fitter than controls at both temperatures, but the difference in fitness was much greater at the lower experimental temperature. Smaller males did not perform significantly differently from controls at either experimental temperature. These findings suggest that thermal selection for larger adult males is at least in part responsible for evolution of larger body size at lower temperatures in this species. An investigation into the evolution of plasticity of body size traits was performed. The phenotypic plasticity of body size and its components; cell size and cell number, were examined by rearing populations of flies that had evolved in constant and variable thermal environments at two different experimental temperatures. Plasticity of body size was comparable among all of the populations examined, however, plasticity of both cellular components of body size was significantly greater in flies adapted to variable thermal environments. The lifespan and fecundity of eight replicated populations of continually mated flies from a cline along the Eastern coast of Australia, when maintained at two different temperatures in the laboratory, was also examined, and no latitudinal trend in either longevity or lifetime fecundity was observed. However, there were some differences in the pattern of fecundity over the lifetime of individuals along the cline.

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