Females of the grasshopper Chorthippus parallelus (Zett.) do not remate for fresh sperm

Abstract

The evolution of female multiple mating is still a largely debated ¢eld. Among the bene¢ts that have been proposed to explain this risky behaviour is the replenishment of sperm reserves. Apart from an increase in total sperm number, it can be an expression of post-copulatory mate choice or can be directed towards the uptake of fresh sperm. Using fresh sperm for fertilization instead of sperm aged by storage in the female genital tract may avoid a lowered fertilization capacity, an increase in deleterious e¡ects or a skewed o¡spring sex ratio. We investigated the in£uence of sperm age on female ¢tness in the grasshopper Chorthippus parallelus, a species where females mate multiply. After copulation, females store sperm over the course of weeks until fertilization. An average ejaculate of 250 000 spermatozoa exponentially declined with time within the female's spermatheca. The number of days since copulation better explained the variation in actual sperm number than the number of pods or eggs laid. We investigated di¡erences in female ¢tness parameters in two treatments. In the ¢rst, females were mated only once, while in the second, females always had freshly ejaculated sperm available. Although in our experiment, multiply mated females had heavier o¡spring than singly mated females, egg number per pod, hatching and fertilization success, their composite e¡ects and o¡spring sex ratio did not vary with respect to season or sperm age. We therefore reject the hypothesis that the reason for remating in females of this species is the uptake of fresh sperm.

Sperm numbers vary between inter- and intra-population matings of the grasshopper Chorthippus parallelus

“…This was not tested in the present paper but it was found that matings reduced sperm numbers in future matings for at least 1 day (i.e. approximately 5% of a male's lifetime): in three populations of C. parallelus (including E and P), ejaculate sizes declined from 100 to less than 10% with one recovery day between copulations but did not decline if there were 4 days in between (K. Reinhardt 1999Reinhardt & 2002.…”

“…I used an established sperm count protocol (Reinhardt et al 1999;Reinhardt 2001) to measure ejaculate size. Potential manipulations of sperm by females did not affect the results because the entire spermathecal tract was removed from the female within 30 min of copulation.…”

Effects of parental age at mating on the fecundity and progeny sex ratio of Campoletis chlorideae, an endolarval parasitoid of the pod borer, Helicoverpa armigera

“…The quantity and quality of stored sperms are constraints acting on female fecundity. Arguments summarized by Reinhardt et al (1999), advocate that a decrease in sperm quality and quantity occurs with sperm age, resulting in a decrease in probabilities of fertilization and hence in female fitness. The increase in progeny sex ratio with increasing age of parents may result from several factors operating at a time.…”

Comparison of the mating behaviour of a bush cricket in the laboratory and the field: Calling activity and mating frequency of a long-winged species, Phaneroptera falcata (Ensifera: Tettigoniidae)

“…One female collected from the field, was mated three weeks later and examined in the laboratory one week after she mated. Sperm counts were done using a modified version of the method used by Reinhardt et al (1999). Briefly, the female was dissected and her spermatheca removed, placed in 0.2 ml of locust saline and slightly ruptured.…”