Sexual selection and extrapair fertilization in a socially monogamous passerine, the zebra finch (Taeniopygia gullata)

We investigated paternal exclusion rate (the percentage of youngreared by a male that were not his genetic offspring), and behavioraland reproductive variables influencing this rate, in a freelybreeding laboratory population of zebra finches (Tae-niopygiaguttala castanotis), a socially monogamous grassfinch. Priorto the experiment, each male founder was fitted with eithertwo red bands (creating a phenotype previously demonstratedto be attractive to females) or two green bands (unattractiveto females) as part of a unique combination of four leg bands.The overall paternal exclusion rate was 28%, as determined bymultilocus, minisatellite DNA fingerprinting of 278 offspringreared by 26 males and their mates. Mean exclusion rates were16% and 40% for red- and green-banded males, respectively. Exclusionrates were directly proportional to rates of female participationin unforced extrapair copulations (UEPCs) with red-banded malesthat occurred when females were fertile. Rates of fertile, forcedextrapair copulations (FEPCs) and fertile UEPCs involving green-bandedmales either failed to influence exclusion rate or varied inverselywith exclusion rate, indicating that extrapair fertilization(EPF) is under female control. Effort devoted by males to seekingEPFs increased exclusion rate. Results suggest that males placegreater effort into seeking fertile versus infertile EPCs andthat unattractive males accrue fitness gains through high parentalinvestment (PI), whereas attractive males benefit through decreasedPI and increased allocation to EPF.