lay his eggs in the nest of others and let them do the whole job, at the risk of losing his bonles. The parasitic life of the cuckoo has made a lot of ink flow, including in these columns. What we know less is that this way of life is not reserved for the favorite species of Swiss watchmakers. In the long evolutionary story of the birds, the “brood parasitism”, since this is its name, thus appeared independently by seven times: three times in different points of the cuculid family; in the indicators of Africa and Asia; Among America’s vachers; In black-headed heterontes, a very special species of South American ducks; And finally in the weavers of Africa.
For fifteen years, the South African ornithologist Claire Spottiswood, Professor in Cambridge, and his colleague Michael Sorenson, from the University of Boston, follow the facts and gestures of this little sparrow, a kind of large-beak pinson At the particularly pronounced sexual dimorphism. The males have a superb bright yellow set when the females conceal it with brown stripes. To lay in the nest of others, it is better to play it discreet.
But the true exploit of weavers is elsewhere: in the ability to imitate the appearance of the eggs of their hosts. The species is not content with a single target. Over time, she learned to copy the shape, size but especially the color and drawing of the shells of four different species, sometimes even several drawings within the same species. The stake is obviously essential: if it marks the intruder, the hostess drills the egg and the story stops. If the cunning succeeds, it will feed the little hacker until his flight, to the detriment of his own offspring.
on the trail of the chromosome w
For a century, this armament race poses a riddle to scientists: How does Lady Weave to convey the good drawing to his daughters? As everyone knows, the genetic characters of the little ones come from both parents. Would the female be able to choose a male with the same phenotype? In 1933, the British geneticist Reginald Punnett proposed an alternative hypothesis: and if the character was carried by the chromosome W, this female sexual chromosome equivalent in birds in our species, which, on the other hand, is masculine? So far, the demonstration had failed in other feather pests. But, in the Accounts from the Academy American Sciences (PNAS) April 11, the two scientists and their Zambian colleagues make justice to Punnett. Thanks to the DNA records carried out on 196 sparges passed by 141 nests, they could prove that the mother alone transmitted to his daughters the good “brushstroke”, and that it was no longer wrong.
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