Natural Selection and Life History Variation: Theory plus Lessons from a Mosquito

Abstract

In theory, life history patterns and polygenic variation in fitness characters provide the selection regimes and essential raw material for microevolution. Over the geographical range of a species, fixed, genetic differences in life history patterns are the result of past microevolution. In any local population of a species, the dynamic interrelations of genetic variation, life history phenomena and natural selection may be observable. For longer-term geographical patterns to continuously or recurrently change, there must persist local genetic variability for at least some of the fitness characters, and there is now considerable evidence that this type of genetic variation, either expressed or potential, is common in natural populations (Istock 1981). Geographical differentiation within a species implies past directional selection, while the conservation of genetic variability in local populations implies the predominance of some form of stabilizing selection. In this paper I will present theoretical and empirical results from studies with the pitcher-plant mosquito, Wyeomyia smithii, which expose both geographical and local genetic variation and something of the dynamic processes of stabilizing selection occurring at the local level.