PATERNITY OF OFFSPRING IN MULTIPLY-MATED FEMALE CRICKETS - THE EFFECTOF NUPTIAL FOOD GIFTS AND THE ADVANTAGE OF MATING FIRST

The spermatophore transferred by male decorated crickets (Gryllodes si gillatus) includes a large gelatinous mass, the spermatophylax, that i s consumed by the female after mating. This nuptial gift preoccupies t he female while sperm are discharged from the remaining portion of the spermatophore, the sperm ampulla, into her reproductive tract. There is considerable variation in the mass of the spermatophylax, and about half of all males produce spermatophylaxes that are too small to ensu re complete sperm transfer. We tested two hypotheses concerning the ma intenance of this variation: (i) males trade-off investment in spermat ophylaxes against copulation frequency; and (ii) males synthesize the largest spermatophylaxes of which they are physiologically capable. Ma les synthesizing large and small food gifts were permitted multiple ma ting opportunities viith the same females, and allozyme markers were u sed to establish the paternity of offspring. There was a significant a dvantage to those males that mated first irrespective of gift size. Th is advantage probably arose, in part, because the sperm of first males would have had exclusive access to females' eggs during the first 24 hours of oviposition, and underscores the benefits of matings with vir gin females. The paternity of 'small-gift' males increased with gift m ass, but there was no such increase in 'large-gift' males. This differ ence probably stems from the relationship between gift mass and sperm transfer: most of the gifts of the large-gift males would have been ab ove the threshold needed to achieve complete inseminations, whereas th ose of small-gift males would have been below the threshold. Within ma ting-order positions, there was no significant difference in the pater nity of large-gift and small-gift males, a result seemingly consistent with the 'trade-off' hypothesis. However, there was no correlation be tween spermatophylax mass and male mating frequency so that the mechan ism by which small-gift males offset their fertilization disadvantage remains unknown.