Cuckoos are nest parasites, meaning they lay their eggs in other birds' nests. The female cuckoo has to lay eggs that mimic the color, size, and shape of the eggs of the host bird. Using a massive data set, including data from museum eggs that are over 100 years old, researchers from the Norwegian University of Science and Technology (NTNU)an colleagues have determined how the ability to lay blue eggs is inherited in cuckoos. For roughly a century, researchers have been trying to figure out how different female cuckoos manage to lay such a variety of different egg colors to match different host birds. The short answer is that "the female bird decides everything," says researcher Frode Fossøy. Fossøy is part of the cuckoo research group at the Department of Biology at NTNU. The results of the group's work were published on Jabuary 12, 2016 in an open-access article in Nature Communications. "We've been able to show for the first time that the blue egg color is inherited via the female cuckoo only. The father has no effect on the color of his daughter's eggs," says Fossøy. Researchers have investigated a wide variety of samples from Europe and Asia. They found a clear relation between blue eggs and genetic material that only comes from the mother (mitochondrial DNA), and no relation between egg color and genetic material that comes from both parents (nuclear DNA).Cuckoos (Cuculus canorus) are parasitic. Female cuckoos lay their eggs in the nests of other bird species, as is well known. The young cuckoo then usually throws the other chicks out of the nest, getting rid of any competition for the parents' attention.Potential host birds develop traits to prevent being tricked by the parasites—they get rid of eggs that don't look like their own.
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