The effect of predation risk on post-copulatory sexual selection in the Japanese pygmy squid

Abstract

Conspicuous male sexual traits (e.g. weapons for male-male competition and displays for courting females) may attract predators. Under conditions of high predation risk females typically become less choosy with respect to mates to reduce the time spent on mate selection. However, post-copulatory sexual traits, such as sperm ejaculation for sperm competition and sperm removal for cryptic female choice (CFC), may increase with predation risk because they are more inconspicuous to predators. To examine this hypothesis, we observed the reproductive behaviour in the Japanese pygmy squid, Idiosepius paradoxus, in which the male attaches ejaculated spermatangia to the female's body and the female removes the spermatangia after copulation. Squid from two populations (Ohmura and Oki), with low and high predation levels respectively, were copulated in tanks under controlled presence/absence of predator conditions. Among the Ohmura individuals spermatangia removal was suppressed in the presence of a predator. Females may not be able to remove spermatangia effectively when facing a predator because they feel threatened by the predator; as a result, more spermatangia were retained during trials in which they were exposed to predators. In contrast for squid from the Oki (high predation) population, which is exposed to a higher predation risk, were not strongly affected by the predator presence. While the males ejaculated more spermatangia, the females removed more of them. The effect of sexual conflict may be greater than that of the predation risk in the pygmy squid. This suggests adaptive differences in post-copulatory sexual selection traits linked to predation.

Immediate predation risk alters the relationship between potential and realised selection on male traits in the Trinidad guppyPoecilia reticulata

“…For example, female water striders perceiving a risk of predation are more likely to accept matings they would otherwise avoid, particularly with large males [13,14]. Similarly, females of pygmy squid Idiosepius paradoxus remove fewer forcibly inserted spermatangia in the presence of predator cues [15], with possible effects on sperm competition.…”

Imminent risk of predation reduces the relative strength of postcopulatory sexual selection in the guppy

“…Indeed, IPR can affect female sexual responsiveness [36] and choosiness [37,38]. Postcopulatory sexual traits are generally inconspicuous to predators [39], and probably, for this reason, the effect of IPR on postcopulatory sexual selection has received relatively less attention. However, sperm competition is mediated by female polyandry [40], which is likely to vary under IPR ( [41], but see [42]), possibly weakening the strength of sperm competition.…”

Immediate predation risk alters the relationship between potential and realised selection on male traits in the Trinidad guppy Poecilia reticulata

“…For example, female water striders perceiving a risk of predation are more likely to accept matings they would otherwise avoid, particularly with large males (14, 15). Similarly, females of pygmy squid Idiosepius paradoxus remove fewer forcibly-inserted spermatangia in the presence of predator cues (16), with possible effects for sperm competition.…”