Evolution and plasticity of body size of Drosophila in response to temperature
Ectotherm body size is positively correlated with latitude, giving rise to body size clines, found in different continents. Ectotherm body size also shows a developmental response to temperature, increasing at lower developmental temperatures. To investigate the effects of temperature in the evolution and plasticity of body size dines, I used two species of the genus Drosophila as model organisms. To investigate the cellular mechanism underlying the evolution of wing size clines the two newly established D. subobscura wing size clines in the Americas were compared with the ancestral European dine. Clinal differences in Europe and South America were due to changes in cell number, whereas clinal differences in North America are due to changes in cell area. These results suggest that the cellular mechanism underlying the establishment of wing size clines is contingent and not predictable. The genetic control of body size in the D. melanogaster South American body size cline was investigated by means of QTL mapping. The results found in South America were consistent with those previously found in Australia, and in both continents the inversion In(3R)P was associated QTL controlling wing area. Genes of the insulin signalling pathway, known to affect size, were characterized in their effects under different temperature and larval crowding regimes. The evolution of plasticity of body size traits was analysed using different thermal selection regimes. The phenotypic plasticity of wing size and its cellular components was examined by rearing flies, selected under fixed or variable thermal environments, at two different experimental temperatures. Plasticity of wing size did not vary among the different selection lines, however, plasticity of both cellular components of body size did. Costs and benefits of adaptation to cyclical thermal environments were assessed with larval competition assays and by assessing size when all lines were reared under cyclic thermal conditions.