Genetic evidence for mixed broods and extra-pair matings in a socially monogamous biparental cichlid fish

Mobile young under parental care have a high potential for intermixing with other broods, which potentially increases the costs to the foster parents. Here, we examined for the first time the genetic composition of wild-caught broods of the convict cichlid (Amatitlania siquia), a socially monogamous biparental fish, for evidence of brood mixing and adoption. Our microsatellite genotyping data revealed that 79% of broods contained adopted young. Moreover, 25% of broods contained adopted sibsets likely arising from extra-pair matings, a phenomenon hitherto not documented for this species. Overall, adopted foreign fry and host fry in mixed broods were generally different in body length, as would be expected if they have different parents. However, fry from possible extra-pair matings were similar in body length to host fry, suggesting that they are of similar age. Our results are important because they reveal a very high prevalence and degree of brood mixing, and indicate that social monogamy does not necessarily lead to genetic monogamy in the convict cichlid in nature. These findings raise questions about potential brood-mixing mechanisms and the reproductive ecology (especially opportunities for polygamy in nature) of this important model species in the study of animal behaviour.