Reproductive behaviour of the ocean skater Halobates robustus (Hemiptera: Gerridae) in the Galapagos Islands.

Field observations on the ocean skater, Halobates robustus Barber showed that the flotillas of adults, unlike those of juveniles, occurred very close to the shore at specific sites from which they were not easily dislodged.The adult flotillas consisted of small all-male groups or aggregations of males and copulating pairs. The proportion of free males in copulating flotillas decreased with increasing group size. There was no correlation between the sizes of the paired males and females.Single adult females, which were not observed in the copulating flotillas, were usually teneral with undeveloped eggs. In contrast, the copulating females contained numerous well-developed eggs. The pairs remained in prolonged genital contact.The behaviour of free males in copulating flotillas was characterized by frequent, non-random encounters with copulating pairs. Experiments with marked individuals established that male take-overs can occur within flotillas.It is concluded that the copulating flotillas are initiated by the males and not only provide protection from predators, as previously shown, but also act as arenas for mate finding and selection. It is presumed that prolonged copulation reduces sperm competition between contending males.