Mate feeding, offspring investment, and sexual differences in katydids (Orthoptera: Tettigoniidae)

Abstract

Food stress in the katydid Requena veriicalis (Orthoptera: Tettigoniidae) decreases the relative availability of males able to supply nutritious spermatophores to females and increases the value of the male courtship meal (i.e., relative male parental investment). These changes cause female sexual competition in katydid populations. Here we examine the effect of food stress on male and female investment in single offspring and test the prediction that male-derived nutrients in eggs increase relative to nutrients from the female's reserves. We varied the diet of female R. veriicalis and determined the fate of nutrients from male and female sources using I4C and 3H radiolabeled amino acids. Low-diet females retained more nutrients from male and female sources in somatic tissues and invested less in reproduction both because they produced fewer eggs and because they invested less per offspring (egg) than females maintained on a high-quality diet. Moreover, opposite to our prediction, relative male investment in individual eggs decreased in foodstressed females; females retained more nutrients in somatic tissues from the male source than the female source. Food-stressed females may retain nutrient reserves, particularly those from the male, as an adaptive trategy for immediate survival needs and future reproduction. Such a female strategy is unlikely to compromise male reproductive success; first-male sperm precedence means that males mating with virgin females are likely to father most eggs laid, even in future reproductive bouts. The decrease in male investment in eggs of low-diet females does not conflict with the contention that relative parental investment controls male intrasexual competition because, in mate-feeding species, male investment influencing this competition includes more than investment in current offspring; females should compete for males if courtship gifts aid survival and later reproduction.