MATE FEEDING, OFFSPRING INVESTMENT, AND SEXUAL DIFFERENCES IN KATYDIDS (ORTHOPTERA, TETTIGONIIDAE)

Food stress in the katydid Requena verticalis (Orthoptera: Tettigoniid ae) decreases the relative availability of males able to supply nutrit ious spermatophores to females and increases the value of the male cou rtship meal (i.e., relative male parental investment). These changes c ause female sexual competition in katydid populations. Here we examine the effect of food stress on male and female investment in single off spring and test the prediction that male-derived nutrients in eggs inc rease relative to nutrients from the female's reserves. We varied the diet of female R. verticalis and determined the fate of nutrients from male and female sources using C-14 and H-3 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 t o our prediction, relative male investment in individual eggs decrease d in food-stressed females; females retained more nutrients in somatic tissues from the male source than the female source. Food-stressed fe males may retain nutrient reserves, particularly those from the male, as an adaptive strategy for immediate survival needs and future reprod uction. Such a female strategy is unlikely to compromise male reproduc tive success; first-male sperm precedence means that males mating with virgin females are likely to father most eggs laid, even in future re productive bouts. The decrease in male investment in eggs of low-diet females does not conflict with the contention that relative parental i nvestment controls male intrasexual competition because, in mate-feedi ng species, male investment influencing this competition includes more than investment in current offspring; females should compete for male s if courtshifts aid survival and later reproduction.