The Cuckoo-weaver is a charming little passerine bird with a bright yellow belly, endemic to southern Africa. It is also a parasite of other species of no less charming birds, the modest Prinia, with its white belly and brown wings, and the red-faced Cisticola.
The female Cuckoo-weaver has developed an extraordinary gift for mimicking the pattern and color of her host’s eggs. It is all the more interesting that the latter, if he discovers the deception, will hasten to pierce the shell of the intruder with his beak before getting rid of it. The Cisticola has thus become particularly adept at spotting a “false”.
But if the cuckoo-weaver’s maneuver pays off, its offspring will have a big advantage, because its chick is hatched a day or two before its competitors. Significantly larger than the latter, it will then capture most of the beak provided by the host parents, convinced to feed their young, and guarantee the legitimate chicks death by starvation.
Everything therefore rests on the ability of the female cuckoo to imitate as perfectly as possible the appearance of the egg of its host. A British geneticist, Reginald Punnett, hypothesized in 1933 that this gift was genetically inherited through the mother.
The team led by the South African evolutionary biologist Claire Spottiswoode, professor at the University of Cambridge (United Kingdom) and that of Cape Town (South Africa), finally brings the proof, in a study published this week. in the Proceedings of the American Academy of Sciences (PNAS).
With the help of young Zambians, she studied the genetic heritage of Cuckoo-weaver populations and their hosts. The female of the parasitic bird transmits to her offspring the ability to lay eggs often resembling those of her host species. That is, to the species in whose nest it itself was born.
This association between a species and its parasite is so close that about two million years ago, the Cuckoo-weaver evolved into two branches: one associating with the Red-faced Cisticola and the other with the Prinia. modest.
The latter lays white eggs pulling more or less towards blue or towards red. The cuckoo has followed this evolution, but can only lay eggs of one color, and relies on luck to match that of its host’s eggs.
The female inherits and transmits alone the ability to produce eggs of a very particular color. A specialization that has become a handicap. Because the Prinia uses the genetic heritage of both parents to lay eggs with ever more diverse patterns and colors.
It thus began to lay eggs of a pretty olive green, a combination using in particular red and blue pigments, which the cuckoo, specialized in only one of the two pigments, cannot imitate. A form of genetic rebellion.
However, if the cuckoo still passes the detection test for its egg, its offspring is certain once and for all to be welcomed. The hosts seem completely silly and raise a cub that looks nothing like their offspring.