Genetic variation in all-or-none life-history traits of the lacewing Chrysoperla carnea

Abstract

Aestival reproduction varies qualitatively within many western North American populations of the Chrysoperla carnea species complex; during the summer, individuals either reproduce or enter reproductive diapause. The expression of this all-or-none phenotypic trait is determined by two ecophysiological response patterns: response to photoperiod and response to prey. These response patterns also vary qualitatively. Artificial selection on the reproductive phenotype significantly altered both the pattern of reproduction and the ecophysiological responses that control reproduction. In populations from western North America, the propensity for aestival reproduction is polygenically inherited, and the trait has considerable genetic variability. This variation occurs in two forms: (i) some is expressed currently and is immediately subject to natural selection (actual variation), and (ii) some is expressed in later generations and therefore is subject to natural selection only after recombination (hidden variation). Both forms of variation are important in the evolution of polymorphic seasonal cycles and seasonally diversified geographical populations.