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Laura Klappenbach

'Cassinova Gene' Drives Female Birds to Cheat

By June 17, 2011

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Scientists once thought birds were the hallmark of fidelity, that most species form devoted pair bonds in which males and females are faithful to one another and cooperate to raise their young. But now, scientists from the Max Planck Institute for Ornithology have discovered that birds aren't as faithful as they had previously thought.

Dr. Wolfgang Forstmeire and his collegaues have found evidence for what is being dubbed as a 'Casanova gene' in birds. The gene is thought to influence how faithful birds are to their mates. In particular, the Casanova gene may drive female birds to cheat, even if such behavior exposes them to a variety of other risks.

Cheating in otherwise monogomous species is complicated. For males, the benefits are more straightforward that for females. When males mate outside their pair, they are able to father more offspring than they would if they had remained faithful. But for females, the benefits are fewer. Cheating females are at risk of contracting sexually transmitted diseases and their mates may withdraw parental care if they suspect cheating has occurred.

Forstmeire and his team conducted an eight-year study of more than 1500 zebra finches to find out more about why female birds cheat. They found that felmales whose fathers cheated, were themselves more likely to cheat too. This means that mating behavior in males is genetically linked to mating behavior in females. Since it's advantageous for males to cheat, females followed suit, even though there are added risks for females. The risks to females are trumped by the benefits to males.


Forstmeier, W., Martin, K., Bolund, E., Schielzeth, H., & Kempenaers, B. (2011) Female extrapair mating behavior can evolve via indirect selection on males. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1103195108

Photo © MPI for Ornithology.

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