Some cichlids are secretly monogamous

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Monogamy is something that some cichlids like to keep a secret, according to a paper to be published in a forthcoming issue of the journal Biology Letters.

Tetsumi Takahashi and colleagues discovered that the Lake Tanganyikan cichlid Xenotilapia rotundiventralis remains socially monogamous even without spending considerable time in close proximity to each other.

Xenotilapia rotundiventralis is a relatively small cichlid (only about 5cm/2" long) that lives and breeds in vast schools consisting of thousands of individuals. This species mouthbroods, with females observed to transfer young from their mouths to males (presumably the fathers) in the same school.

However, their propensity to congregate and general lack of markings (making it difficult to distinguish one individual from another) makes it difficult to ascertain if the males (to which the young are transferred) are indeed the biological fathers.

Takahashi and his coauthors have confirmed by conducting a parentage analysis using ten microsatellite markers of the young and the two fish involved in the transfer, that the males are indeed the biological fathers.

The results suggest that each female broods offspring that she has laid and that each male receives the young that he has fertilised from his mate.  Therefore, the mating pairs most likely maintain the pair bonds at least until the female-to-male shift of young occurs.  

The authors consider this to be the first study identifying pair bonds in animals in which physical proximity of the pair members has not been observed.

For more information, see the paper: Takahashi, T, H Ochi, M Kohda and M Hori (2011) Invisible pair bonds detected by molecular analyses. Biology Letters doi:10.1098/rsbl.2011.1006

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