Experimental analyses of costs and benefits of wing length polymorphism in grasshoppers.

摘要

Ecological and evolutionary aspects of wing length polymorphism are tested using grasshopper species. The primary cost associated with reduced wing lengths is assumed to be decreased flight capability. The correlated benefit is increased allocation of resources to reproduction. The objective of my research was to examine each of these assumptions in laboratory and field experiments. I focused the research on Phoetaliotes nebrascensis (Thomas), a wing dimorphic species, and included observations on other, resident species exhibiting continuous wing length variation, Ageneotettix deorum (Scudder), Amphitornus coloradus (Thomas), and Spharagemon collare (Scudder).;Both high population densities and low quality food (% total nitrogen) are necessary to stimulate development of long-winged individuals in the laboratory. Evidence from selected lines indicated that there was a heritable component to the wing length trait; wing length frequencies among long- and short-winged lineages diverged significantly after one generation. Detailed observations of life history characteristics in these lineages and field caught individuals established two findings: (a) short-winged individuals experience a reproductive benefit and (b) reproductive capabilities, in the laboratory and field, are strongly divergent, extrapolations should be made with caution.;Mark-and-recapture studies addressed costs of reduced wing lengths relative to dispersal capability. Evidence from group releases and individual marking experiments showed no relationship between wing length and distance moved; they provide little support for the assumption of a cost in movement ability. In general, grasshoppers move short distances during their lifetimes and there is no apparent benefit to increased wing lengths relative to displacement.;Finally, I suggest conceptual hypotheses addressing potential areas for future analyses in the dynamics of wing-length polymorphism at the population level; grasshopper developmental sequences, host plant phenology, abiotic influences, etc., are linked within a common, schematic framework. When environmental factors deteriorate, populations across large geographic areas can be adversely affected. Comparisons suggest that different community compositions are important and indicate that generalizations aimed toward "generic" grasshoppers and locusts are misleading.