Why some cuckoos have blue eggs

Cuckoo eggs come in a wide variety of colors and patterns, but why?

Date:January 21, 2016

Source:Norwegian University of Science and Technology

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. Now, a group of researchers at the Norwegian University of Science and Technology (NTNU) has come up with an answer to this puzzle, in cooperation with researchers from all over Europe and Asia.

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 have just been published 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.

Read on ...

Unscrambling the Genetics of the Chicken's 'Blue' Egg

Aug. 20, 2013 — Researchers at The University of Nottingham have unscrambled the genetic mutation that gives the distinctive blue eggs laid by some breeds of chickens.

They are the latest foodie fashion and look set to become big business in the baking aisles of all the major supermarkets -- the blue egg produced by some chickens is prettier and some say tastier and cleaner-breaking than the traditional brown one -- and now, thanks to scientists from The University of Nottingham, we know what caused the eggs in some breeds to turn this unusual colour.

In a four-year research project just published in the journal, PLOS ONE, the team from the School of Biology, has identified the genetic mutation which first produced the blue egg in native South American chicken, the Mapuche fowl, and their European descendants, Araucana between 200 and 500 years ago. The results could inform future research into agricultural breeding techniques if demand for the blue egg continues to grow.

The scientists used the unique genetic resources conserved by heritage or 'fancy' poultry breeders to identify at fine resolution the exact location of the mutation in the genome in blue egg laying chicken. This work was followed by further genomic study which revealed the genetic cause of the blue coloured egg shell -- surprisingly -- an ancient harmless retrovirus in the domestic chicken.

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