Copulation patterns and mate guarding in the sex-role reversed, polyandrous spotted sandpiper, Actitis macularia

Abstract

Abstract. Females in polyandrous mating systems have many opportunities for extra-pair copulations. Males, however, are primary caretakers of eggs and chicks in most polyandrous systems, and this sex-role reversed pattern of caretaking is unlikely to evolve unless males have high certainty of paternity. Thus, well-developed behaviour patterns for ensuring within-pair paternity in sex-role reversed species are expected. Paternity assurance was examined in the polyandrous, sex-role reversed spotted sandpiper, Actitis macularia , to determine whether copulation pattern and timing favoured paired males in sperm competition, and whether males were closer to their mates during egg laying. Female behaviour during extra-pair copulation attempts was also examined. Within-pair copulation rates changed significantly across the nest cycle, peaking the day before the first egg was laid. Within-pair copulation rate also was higher when female absence from the territory was high. Observed copulation rates were higher for a female's first mate than for subsequent mates. In 1990, 81% of the copulations occurred within 1 min of either mate's return from off territory; in 1976-1977, 30% bad this timing. Males did not spend more time close to their mates during egg-laying, but usually females rejected, or were neutral to, extra-pair copulation attempts. Observed patterns of copulation rate and timing should increase a paired male's advantage in sperm competition. These results suggest that both sexes exhibit patterns of paternity assurance, although it is less stringent and more selective in females.