Dt. Gwynne et Wd. Brown, MATE FEEDING, OFFSPRING INVESTMENT, AND SEXUAL DIFFERENCES IN KATYDIDS (ORTHOPTERA, TETTIGONIIDAE), Behavioral ecology, 5(3), 1994, pp. 267-272
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.