RESOURCE INFLUENCED SEX ROLES OF ZAPROCHILINE TETTIGONIIDS (ORTHOPTERA: TETTIGONIIDAE).

Abstract

Male tettigoniids donate nutrients to females at mating in the form of a spermatophylax. Male-donated nutrients function as paternal investment leading to a reversal in the sex roles of males and females. Reversal in the behavioral sex roles of a zaphrochiline tettigoniid was found to be directly related to the current availability of food resources in the environment. When resource availability was low, females were less fecund and males had lower and more variable accessory gland weights (the spermatophylax producing gland) than when resource availability was high. When resources were scarce, larger individuals had a reproductive advantage having more eggs or heavier accessory glands. All individuals were equally fecund or had equal accessory gland weights when resources were plentiful. During low resource availability males that had a spermatophylax to offer were choosy of their mates, and females were competitive. When resources were plentiful, males were less discriminative and females showed signs of discrimination. There was evidence that female sexual motivation decreased when environmental resources were plentiful (as indicated by mating frequency) and that only females of low nutritional status continued to mate. When resources were scarce, females achieved fecundities equivalent to those achieved during high resource availability through spermatophylax consumption. These data support the hypothesis that females continue to mate to compensate for low resource availability and that male parental investment may be important only in poor quality habitats. When resources are plentiful females do not need to remate. Thus resource availability may directly influence the number of sexually active males and females (operational sex ratio) and the form of sexual selection.