Habitat Persistence and the Evolution of Wing Dimorphism in Insects

Abstract

Wing dimorphism occurs commonly among many species of insects. This dimorphism is hypothesized to be maintained by a trade-off between the costs of being macropterous (winged, flight capable) and the long-term benefits of migration in a heterogeneous environment. In this article this hypothesis is investigated with a simulation model consisting of an environment composed of discrete patches that persist for a fixed period and a generalized life-history pattern. The analysis shows that a dominant brachyptery (rudimentary wings, flight incapable) allele can readily spread in a monomorphically macropterous population and that at equilibrium genetic variability is maintained. The invasion of the brachyptery allele depresses population size but enables the population to spread into regions in which the monomorphically macropterous population cannot persist. Further analysis of the model shows that patch persistence time (T), the cost of being macropterous (c), the proportion of migrants (m), and the probability of locating another patch (s) are all important in determining the frequency of macroptery but that T and c are the most important. The model predictions are compared with data on planthoppers: an excellent fit is obtained. This fit is robust to parameter values for persistence times greater than five generations. The implications of this model with respect to the evolution of migration and dimorphisms are discussed.