Sperm storage mediated by cryptic female choice for nuptial gifts

Abstract

Polyandrous females are expected to discriminate among males through postcopulatory cryptic mate choice. Yet, there is surprisingly little unequivocal evidence for female-mediated cryptic sperm choice. In species in which nuptial gifts facilitate mating, females may gain indirect benefits through preferential storage of sperm from gift-giving males if the gift signals male quality. We tested this hypothesis in the spider Pisaura mirabilis by quantifying the number of sperm stored in response to copulation with males with or without a nuptial gift, while experimentally controlling copulation duration. We further assessed the effect of gift presence and copulation duration on egg-hatching success in matings with uninterrupted copulations with gift-giving males. We show that females mated to gift-giving males stored more sperm and experienced 17% higher egg-hatching success, compared with those mated to no-gift males, despite matched copulation durations. Uninterrupted copulations resulted in both increased sperm storage and egg-hatching success. Our study confirms the prediction that the nuptial gift as a male signal is under positive sexual selection by females through cryptic sperm storage. In addition, the gift facilitates longer copulations and increased sperm transfer providing two different types of advantage to gift-giving in males.

Figure 1.

(a) Number of sperm in the female sperm storage organs and (b) hatching success, in NG (short copulations without gift), GT (short copulations with gift) and G matings (long copulations with gift). Asterisk (*) indicates significant differences (p < 0.05).

Figure 2.

(a) The number of sperm stored in female sperm storage organs as a function of copulation duration in NG (short copulations without gift) and G (long copulations with gift); and (b) proportion of hatched eggs as a function of copulation duration in the NG and G groups. Statistics were performed using GLM with Poisson (sperm number) and binominal function (hatching success) and log link (see text). Filled circles, G group; open circles, NG group.