FOOD QUALITY CONTROLS SEXUAL SELECTION IN MORMON CRICKETS BY ALTERINGMALE MATING INVESTMENT

Populations of several katydid species (Orthoptera: Tettigoniidae) sho w large differences in mating system; in some species males compete an d females choose mates, whereas in others these courtship roles are re versed. Male katydids feed their mates during mating with a large, nut ritious spermatophore. I hypothesized that courtship role reversal and increased sexual selection on females was a result of limitation in n utritious food items causing a decrease in the number of males availab le for mating (and thus in the spermatophore meals available). This hy pothesis was tested by varying diet in field cages of Mormon crickets, Anabrus simplex. Results showed that, in contrast to a diet supplemen ted with proteinaceous food items, a poor diet resulted in: (1) a decr ease in the number of sexually active males, (2) an increase in sexual selection for female body size, and (3) a reversal in the typical cou rtship roles. The experiment ruled out alternative explanations for va riation in the mating system of this species, such as differences in p opulation density and age. The conclusion from this study is that incr eased sexual selection on females due to such a change in diet is a re sult of an increase in the relative importance of male parental invest ment.