Evolution of red and grey colour polymorphism in cuckoos

A paper on the evolution and genetic architecture of a polymorphism restricted to cuckoo eggs has been published in the prestigious journal Science Advances. Several scientists from the University of Debrecen have been involved in the work since 2020.

The new study, co-authored by Miklós Bán, assistant professor at the Department of Evolutionary Zoology and Human Biology, Faculty of Science and Technology, and Attila Fülöp, research associate at the department, and former PhD student Attila Marton, published in the prestigious journal Science Advances, provides insights into the genetic basis of the dichromatism in cuckoo egg laying.

- The results of the study show that the feather dichromatism of Eurasian and Eastern cuckoos is linked to a specific genomic region, inherited only on the maternal line, which may have evolved in the common ancestor of both species about a million years ago. Furthermore, the spectroscopic properties of plumage colour are similar in both species, suggesting a common biochemical basis for dichromatism. The study represents a major step forward in unraveling the mysteries of colour polymorphism in cuckoo egg laying and contributes to a better understanding of the genetic basis of the ivarspecific traits in avian evolution," said Attila Marton, whose samples collected in Hungary served as the basis for the research.

The back and throat of the male Eurasian cuckoo, which also breeds in Hungary, and of some closely related species, are slate grey, with a black banded breast on a white background.

- In contrast, the colur of the layers can be either grey, like that of the males, or reddish. This duality has presumably evolved to increase the breeding success of the cuckoos. Cuckoos do not build their own nests, but smuggle their eggs into the nests of other bird species, thus completely delegating parental care. Plumage dichromatism may have been maintained by negative frequency-dependent selection, as host species protected their nests more effectively against more frequent colour variation, the biologist explained.

Genetic analysis of the samples will start in 2020, but the collection of the samples used will start much earlier. The results are mainly relevant for breeding parasitism specialists, but could also be useful for research on other sex-limited polymorphisms.