title: Extra-pair copulation and sperm competition in the zebra finch.
abstract: Most birds are monogamous, but recent studies have shown that extra-pair copulations (EPCs) occur frequently despite a range of paternity guards, including mate-guarding and frequent copulation. Although EPCs are known to result in extra-pair paternity, there are no previous quantitative estimates of the success of EPCs in fertilizing eggs. We present here estimates of the likelihood of success of extra-pair copulations in a monogamous passerine, the zebra finch Poephila guttata. We show that (1) EPCs occurring under semi-natural conditions in captivity result in extra-pair paternity, (2) sperm from the last male to mate has precedence over previous matings: a single EPC occurring last is disproportionately successful in fertilizing eggs, but EPCs followed by further pair copulations have a low probability of success. These results have important implications for sexual selection theory.
authors.affiliation: Department of Animal Biology, The University, Sheffield, UK.
authors.forename: T R
authors.initials: TR
authors.lastname: Birkhead
authors.forename: J
authors.initials: J
authors.lastname: Pellatt
authors.forename: F M
authors.initials: FM
authors.lastname: Hunter
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D003163:Competitive Behavior; D003307:Copulation / Q000502:physiology*; D005260:Female; D008297:Male; D010334:Paternity; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology*