EVOLUTION AND DEVELOPMENT OF BODY-SIZE AND CELL-SIZE IN DROSOPHILA-MELANOGASTER IN RESPONSE TO TEMPERATURE

We examined the evolutionary and developmental responses of body size to temperature in Drosophila melanogaster, using replicated lines of f lies that had been allowed to evolve for 5 yr at 25 degrees C or at 16 .5 degrees C. Development and evolution at the lower temperature both resulted in higher thorax length and wing area. The evolutionary effec t of temperature on wing area was entirely a consequence of an increas e in cell area. The developmental response was mainly attributable to an increase in cell area, with a small effect on cell number in males. Given its similarity to the evolutionary response, the increase in bo dy size and cell size resulting from development at low temperature ma y be a case of adaptive phenotypic plasticity. The pattern of plastici ty did not evolve in response to temperature for any of the traits. Th e selective advantage of the evolutionary and developmental responses to temperature is obscure and remains a major challenge for future wor k.