Birds: Beautiful sons thanks to the mother

Offspring from first eggs of a Legesequenz thrive particularly well

Zebra finch male with characteristic breast and cheek jewelery. © University of Zurich
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Not the good genes of the father, but the initial investment of the mother in their eggs makes zebra finch males particularly beautiful. This has now been found out by a Swiss-Australian research team. According to previous assumptions, it does not play a big role who is the father of the offspring. Rather, the time is decisive, to lay the eggs: The first eggs gedeien particularly well.

Like most birds, Australian zebra finches also attract their young as a couple. But the social father is not always the producer: the females mate with other males when the opportunity presents itself. Interestingly, the offspring of the different fathers differ. Evolutionary ecologists from the University of Zurich, together with biologists from Macquarie University in Sydney, found that sons born to males outside of mating relationships are more beautiful: their colored plumage is more pronounced than that of the genetics of the mated male.

One-time sexual partners are not attractive

So far, it was assumed that such qualitative differences in the offspring stems because the females additionally mate with particularly attractive and thus genetically particularly valuable males outside of the mating relationship. Now Barbara Tschirren, Professor of Evolutionary Ecology at the University of Zurich, and her team refute the theory of the especially good sires and the attractive "superman". As the scientists in the article published in the "Proceedings of the Royal Society B" show, the mated male and the unique sexual partner do not differ in their color splendor. The unique sexual partner is neither more beautiful nor genetically more valuable than the male from the couple relationship.

First laid eggs are preferred

The beautiful sons have their origin not as previously suspected in the good genes of the father, but in the maternal initial investment in the eggs. As Tschirren can show, the maternal investment per egg decreases steadily within the laying sequence. In the first eggs of the mother still a lot of nutrients and hormones are stored - these eggs are also larger than those of the remaining Geleges. This preference for the first laid eggs or first hatched juveniles by the female makes sense, as these offspring have a much higher chance of survival than later hatched.

"Males compete with each other to be able to fertilize the first eggs in the laying sequence of a female, so as to exploit the additional investment of the female in these eggs for their own offspring, " Tschirren explains the new findings. She suspects that ultimately it is a pure sperm competition. Males with the fastest sperm fertilize the best-equipped eggs. (Proceedings of the Royal Society B, 2011, DOI: 10.1098 / rspb.2011.1543) Display

(University of Zurich, 30.09.2011 - NPO)