Although many studies have revealed differences in patterns of extrapair paternity between species and between populations of the same species, possible differences in female extrapair behavior within populations have received far less attention. Here, we propose and test the hypothesis that females of the highly polygynous Red Bishop (Euplectes orix) follow two different extrapair strategies, with benefits of extrapair copulations depending on the quality of their social mate (”conditional-extrapair-strategy hypothesis”). In particular, we propose that females mated to low-quality males enhance the genetic quality of their offspring by performing extrapair copulations with males of higher quality than their social mate (in accordance with the good-genes hypothesis), whereas females mated to high-quality males perform extrapair copulations as insurance against temporary infertility of their social mate caused by sperm depletion due to frequent copulations (in accordance with the fertility-insurance hypothesis). Several predictions derived from our hypothesis, regarding differences in frequency and distribution of both unhatched eggs and extrapair young between high-quality and low-quality males, are tested and shown to be supported. Most importantly, hatching failures occurred more often in territories of high-quality males than in those of low-quality males, and the proportion of unhatched eggs within the territory was positively correlated to breeding synchrony for high-quality males only. Those results suggest that sperm depletion is a risk for females mated to high-quality males with many mating opportunities. The fact that broods of high-quality males without unhatched eggs had a significantly higher proportion of extrapair young than broods of high-quality males with unhatched eggs is consistent with the hypothesis that females mated to high-quality males were successful in performing EPCs as insurance against temporary infertility of their social mates. Furthermore, genetic fathers of extrapair young hatched in territories of low-quality males were found to be of higher quality than the corresponding social fathers, whereas no difference in quality was found between genetic and social fathers of extrapair young hatched in territories of high-quality males. Although we cannot exclude the possibility that the observed pattern was a result of females mating randomly from within the available pool of extrapair males, it is in accordance with our prediction that females mated to low-quality males perform extrapair copulations with males of higher quality than their social mate to enhance offspring fitness. Overall, the data presented here suggest that females within our study colony adjusted their extrapair behavior to the quality of their social mate, even if we cannot entirely rule out alternative explanations for some of the results obtained. Thus, the study provides support for the conditional-extrapair-strategy hypothesis, which states that within populations, females may follow different extrapair strategies to gain different benefits.

Fertilizaciones Extra-pareja en Euplectes orix: ¿Siguen las Hembras Estrategias Extra-pareja Condicionales?