The Evolution of Dispersal Dimorphism and Other Life History Traits in Water Striders (Hemiptera : Gerridae)

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Dispersal dimorphism is a conspicuous adaptation in water striders (Hemiptera : Gerridae) where the flightless adult morph is easily recognized by its distinctly reduced wings. Populations may be either winged, wing dimorphic, or flightless (winged morph rare or missing). In this study, patterns of wing morphism and habitat use are integrated with reconstructed phylogenies (cladograms) for selected genera and species of Gerridae. Ancestral state of wing morphism, number of changes between morphism states, and associations between different traits are traced using the methods of phylogenetic inference. The results of the phylogenetic analyses are discussed in the light of various hypotheses on the evolution of dispersal dimorphism and other life history traits in insects. Ancestral gerrids probably occupied relatively stable, aquatic habitats (lotic or lentic) where the selective balance between wing morphs favoured the flightless morph. The ability to produce winged individuals, however, was only lost completely in species colonizing the extremely stable marine environment. When available habitats became less stable, the selective balance shifted towards the winged morph and the species became permanent dimorphic or monomorphic winged. In temperate regions, many species became seasonally dimorphic with a high frequency of short-winged adults in the direct breeding, summer generation.
2000-03-25