If the females of the house fence king go alien, they get more sons.
Read aloud If the female of the house fence king dares an affair, it is more likely than average male offspring. Thus, the female ensures that as many positive characteristics of the attractive second man in the male line of her offspring are included. An international research team led by Scott Johnson from the University of Towson (USA) has found this out. The researchers thus confirm the assumption that the birds use an infidelity to increase the evolutionary fitness of their offspring. The house fence kings are usually monogamous animals. In about one third of the nests, however, the females raise one or two offspring from a side jump. During the six breeding seasons between 1991 and 1993 and between 2004 and 2006, the researchers examined 2, 345 young birds in a few hundred nest boxes. They took blood samples and certain paternity as well as the sex of the chicks from the juveniles and the presumed fathers. 350 young birds must come from an infidelity of the mother, the researchers found out. Unusually, however, was that among the offspring from the infidel were about eight percent more male than female chicks. On the other hand, the descendants of the breeding pair kept both sexes in balance.

The researchers suspect that the Hauszaunkönig females use the occasional infidelity to secure their offspring high chances of survival. This is especially an advantage if you can transfer as many positive traits of another male as possible to the male descendants through the infidelity. This pays off, say the researchers, as the house fence kings often argue with each other for the limited nesting sites.

Scott Johnson (University of Towson) et al .: Proceedings of the Royal Society B, online pre-release, doi: 10.1098 / rspb.2009.0283 ddp / wissenschaft.de? Martin Schäfer

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