Ejaculate size varies with remating interval in the grasshopper Chorthippus parallelus erythropus (Caelifera: Acrididae)

The number of sperm a male ejaculates is influenced, among other factors, by male age, time since last copulation and possibly a combination of both. Males of Chorthippus parallelus erythropus were subjected to three successive matings in which males had a remating interval of either one or three days. The first ejaculate was very variable. It contained a mean of 433,000 sperm. If there was a one-day interval between matings, the second and third ejaculate comprised 16-19% of the number of sperm in the first ejaculate, respectively. Its sister taxon, the subspecies Chorthippus p. parallelus showed a similar second ejaculate size but the third ejaculate further declined to 8-10% compared to the first. If there were three days between matings, second and third ejaculates comprised 148.3% and 63.1% of the number of sperm in the first ejaculate in Chorthippus p. erythropus. This was markedly different to two individuals of Chorthippus p. parallelus where second and third ejaculates comprised 597% and 416% of the first. It is speculated that this indicates an overall higher sperm production because testis size was also larger in Chorthippus p. parallelus than Chorthippus p. erythropus. The results also show that theoretical models on sperm allocation may underestimate the rate and age-dependency of sperm replenishment.