Risky sex: male pipefishes mate at random in the presence of a predator

Abstract

Abstract. Whether the presence of a predator alters courtship behaviour and mating in male pipefish, Syngnathus typhle, was studied experimentally by first allowing a male to choose between a large and a small female in an enclosure. The females were subsequently released to establish with which the male mated. In the presence of an enclosed predator, males were not more active in front of or danced more with larger than smaller females, but in the absence of a predator the larger females received more activity and dancing. Moreover, control males (without a predator) copulated more often with large than with small females, whereas predator-exposed males copulated infrequently and indiscriminately. These differences are most likely to be due to a decrease in male choosiness when a predator is present, as treatment, size and time of the day did not influence the activity of enclosed females. Predator-exposed males courted and copulated less, but each copulation transferred more eggs, compared with the control males. There was no significant difference in total number of eggs transferred to the males' brood pouches between treatments. Thus, the presence of a predator made mating random and minimized conspicuous mating behaviour, thereby decreasing the potential for sexual selection to act under high predation regimes in this pipefish.