Food Quality Controls Sexual Selection in Mormon Crickets by Altering Male Mating Investment

Abstract

Populations of several katydid species (Orthoptera: Tettigoniidae) show large differences in mating system; in some species males compete and females choose mates, whereas in others these courtship roles are reversed. Male katydids feed their mates during mating with a large, nutritious spermatophore. I hypothesized that courtship role reversal and increased sexual selection on females was a result of limitation in nutritious food items causing a decrease in the number of males available for mating (and thus in the spermatophore meals available). This hypothesis was tested by varying diet in field cages of Mormon crickets, Anabrus simplex. Results showed that, in contrast to a diet supplemented with proteinaceous food items, a poor diet resulted in: (1) a decrease in the number of sexually active males, (2) an increase in sexual selection for female body size, and (3) a reversal in the typical courtship roles. The experiment ruled out alternative explanations for variation in the mating system of this species,such as differences in population density and age. The conclusion from this study is that increased sexual selection on females due to such a change in diet is a result of an increase in the relative importance of male parental investment.