Cuckoos lose the race of coevolution

This is a 90-year-old hypothesis that has just been confirmed by the team led by Professor Claire Spottiswood from the Department of Zoology in Cambridge (UK), Michael Sorenson from Boston University (US) and the Institute of Ornithology in Cape Town (South Africa). In 1933, the British geneticist, Reginald Bonet, known for developing a tool for finding offspring’s ancestors, put forward the hypothesis that parasitism developed by certain bird species is transmitted through the mother. By analyzing the genomes of 196 parasite anomalies (Anomalospiza imberbis) captured in 141 nests of grasshopper birds, which are small beavers that were strongly affected by the intruder, the researchers were able to confirm this hypothesis in this species from South Africa. Their results have just been published in PNAS.

The relationships between the different species of parasitic birds and the hosts forced to raise their offspring date back at least two million years. It is a well-known and well-studied example of the co-borrowing of co-evolution from the Red Queen Theory, a term borrowed from Alice in Wonderland by Lewis Carroll. When a species develops a mutation that allows it to gain an advantage, the species with which it evolves will develop a defense that restores balance. This is what happens to Alice when she runs while the scene moves at her same speed: she has the impression that she is standing still. For parasitic birds, it is essential to maintain this ability to mimic the eggshell of parasitic species, otherwise they will be spotted by their victims and chased from the nest. So there is no doubt that the genes responsible for this ability would be lost if one of the parents was bred by a different host than the mother’s host, which is a huge risk because these parasitic species do not form faithful pairs. Researchers have demonstrated that aberrant aberrations transmit this ability through the female’s W chromosome similar to the male’s Y chromosome in humans. Thanks to this transmission, like Alice, parasites run at the same speed as the landscape.

An arms race that turns in favor of the victims

But this could change. “While this maternal heritage has enabled anomalies to exploit a large number of species, the ability to develop a counter-adaptation is likely to be lost if their host opposes new defences.”explains Claire Spottiswood at the University of Cambridge website. Thus the parasites seem to have a daunting problem because some of the infected species have developed an astonishing array of egg colors that help them distinguish the parasite’s eggs from their own.”

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