Paternity assurance through frequent copulations in a wild passerine with intense sperm competition
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Frequent copulation is assumed to be an important male reproductive strategy for paternity assurance in species with female sexual promiscuity. However, the empirical evidence supporting this hypothesis is limited. We examined copulation behaviour in relation to within-pair paternity in the socially monogamous tree swallow, Tachycineta bicolor, a passerine bird species with frequent copulation, a lack of mate guarding and high levels of extrapair paternity. We found that the frequency of within-pair copulation attempts increased and peaked just before the appearance of the first egg. A marked drop in the frequency of copulation attempts was observed once the first egg was laid. Furthermore, the frequency of successful within-pair copulations was highly repeatable for particular pairs within the 3 days prior to appearance of the first egg. Finally, males that obtained a higher number of successful within-pair copulations during this time also sired a larger proportion of the offspring in their own brood. Our findings suggest that frequent copulations just before the start of egg laying is an adaptation to decrease the risk of being cuckolded in the presence of sperm competition, and thus provide empirical support for the paternity assurance hypothesis. Crown Copyright 2008.
