Abstract
BackgroundWhile many studies have investigated the occurrence of extra-pair paternity in wild populations of birds, we still know surprisingly little about whether individual females differ intrinsically in their principal readiness to copulate, and to what extent this readiness is affected by male attractiveness.Methodology/FindingsTo address this question I used captive zebra finches (Taeniopygia guttata) as a model system. I first measured female readiness to copulate when courted by a male for the first time in life. Second, I conducted choice-chamber experiments to assess the mating preferences of individual females prior to pair formation. I then paired females socially with a non-desired mate and once they had formed a stable pair bond, I observed the inclination of these females to engage in extra-pair copulations with various males. Females showing a high readiness to copulate when courted by a male for the first time in life were much more likely to engage in extra-pair copulations later in life than others. Male attractiveness, as measured in choice tests, was a useful predictor of whether females engaged in extra-pair copulations with these males, but, surprisingly, the attractiveness of a female's social partner had no effect on her fidelity. However, it remained unclear what made some males more attractive than others. Contrary to a widespread but rarely tested hypothesis, females did not preferentially copulate with males having a redder beak or singing at a higher rate. Rather it seemed that song rate was a confounding factor in choice-chamber experiments: song attracted the female's attention but did not increase the male's attractiveness as a copulation partner.Conclusions/SignificanceIntrinsic variation in female readiness to copulate as well as variation in the attractiveness of the extra-pair male but not the social partner decided the outcome of extra-pair encounters.
Highlights
The discovery that extra-pair paternity is both frequent and widespread among socially monogamous birds [1,2,3,4] had a great impact on our understanding of avian mating systems [5,6]
A few studies that have tested whether fidelity of individual females is repeatable across different mating situations, but they did not find significant differences between females [9,10]
Of the 40 females that were unfaithful to their first social partner at least once, only 16 (40%) were unfaithful to their second social partner, and of the 27 females that were never unfaithful to their first partner, nine (33%) were unfaithful to their second partner (Fisher’s exact test: Chi2 (1) = 0.3, P = 0.62). These analyses suggest that, in extra-pair trials, female responsiveness was partly consistent within individual females and partly influenced by male attractiveness
Summary
The discovery that extra-pair paternity is both frequent and widespread among socially monogamous birds [1,2,3,4] had a great impact on our understanding of avian mating systems [5,6]. Despite fairly large sample sizes, field studies might often lack the statistical power required to detect individual differences in female promiscuity This is primarily because field conditions normally do not allow us to observe the readiness of females to engage in extra-pair copulations, but rather limit us to drawing conclusions about female behaviour from patterns of paternity. As measured in choice tests, was a useful predictor of whether females engaged in extra-pair copulations with these males, but, surprisingly, the attractiveness of a female’s social partner had no effect on her fidelity. Contrary to a widespread but rarely tested hypothesis, females did not preferentially copulate with males having a redder beak or singing at a higher rate Rather it seemed that song rate was a confounding factor in choice-chamber experiments: song attracted the female’s attention but did not increase the male’s attractiveness as a copulation partner. Intrinsic variation in female readiness to copulate as well as variation in the attractiveness of the extra-pair male but not the social partner decided the outcome of extra-pair encounters
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