Heritability of Development Time and Protandry in the Pitcher-Plant Mosquito,wyeomyia Smithii

Models of protandry (1) assume implicitly or explicitly that independent evolution of male and female preadult development times is possible and (2) assume or assert that protandry should increase in populations that are univoltine or at least composed of discrete, nonoverlapping generations. Herein we examine these assumptions in the pitcher-plant mosquito, Wyeomyia smithii. Heritability and additive genetic variance of development time are higher in female than in male W. smithii. Protandry is higher in lines selected for slow development than in lines selected for fast development or in unselected control lines. Protandry is therefore capable of evolving. Contrary to predictions based on sexual selection, southern populations with multiple, overlapping generations are just as protandrous as northern bi- and univoltine populations with discrete generations. Voltinism and developmental synchrony of the population do not appear to have been major selective factors in the evolution of protandry in W. smithii. We propose that protandry can be maintained by natural selection in multivoltine populations with overlapping generations as a consequence of sexually dimorphic fitness criteria. Selection should minimize development time in males but maximize growth rate in females. In W. smithii, females achieve higher growth rate than males but also harbor greater genetic variation for development time, indicating that selection has, indeed, minimized development time to a greater extent in males than in females. We conclude that if both natural and sexual selection are involved in the maintenance of protandry in populations of W. smithii, then their relative importance changes with the degree of generation overlap.