N.TOUR CHOICE, as quoted in Charles Darwin ‘s masterpiece, “On the Origin of Species”, explains how organisms grow and adapt to their conditions. Surprisingly, though, it’s a bit hazy on the very subject of the title, which is how parenting sex comes from a new girl’s gender. Darwin recognized that diverse ecological richness encourages profitability (although he did not use those terms that have not yet been established). But he did not question how incompetent girl species were prevented from being remixed before they parted properly.
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Somehow, barriers against miscegenation need to be lifted. They can be geographical – fish in different lochs, for example. Or they could be ecological, such as a shift in food choices causing previously insectivorous insects of the same species to feed in different tree species. But species sometimes form in situations where such barriers are not visible. That’s weird.
One rule-based difference is that separation profiteering must be interbreeding. This is a common source of new plant species, but is rarer for animals. It is thought, however, to describe several groups of brightly colored animals, including the cichlid fish of the Great Lakes of Africa, the heliconid butterflies of South and Central America, and the aquatic- southern capuchino, a family of songbirds that also live in the tropics of the New World. . Now, Sheela Turbek of the University of Colorado, in Boulder, has taken matters a step further, by showing that a process called sexual selection plays a part in what is going on.
Picky, picky
Sexual selection, a phenomenon first scientifically described by Darwin, occurs when one sex (usually the female) chooses another (usually the male) on the basis of a particular genetic trait. The classic example is a peacock tail. But sexual selection could also separate species into a one-step process that is more or less the same, with the sudden appearance of such a character. And that, as she explains in a paper in Science, that is what Ms. Turbek thinks happened in the case of Iberá waters and an earring.
These two birds live, among other places, in the San Nicolás Sanctuary, Argentina. They feed on the same grasses, breed at the same time, and have breeding grounds that can be as close as 50 meters from one in which the other species lives. They are also similar enough to successfully interfaith in captivity. But, as far as is known, they never do that in the country.
Genetic sequences show just how similar these species are. Only 12 of their genes differ – less than 0.1% of their genomes. Interestingly, one of the 12 is part of one of the sex chromosomes, influencing a role for sexual selection. Three others play a role in coloring male feathers, which is also useful. For, although the species are of the same size and shapes, adult seedeaters have orange-brown chests, as the name implies, and Iberá male seedeaters have black necks and sand-colored bodies. Their songs are special too. They use the same frequency range, but different syllables.
First, Ms. Turbeck and her colleagues established that women of both sexes regularly chose the right partners. Proposed pairs were thus observed, and juvenile genetic testing did not find (required by the fact that more than half of the females studied were breeding with males in addition to the participants). their long-term) either. Thus, they looked at male abilities to differentiate obvious competitors from heterospecific nons. In the breeding season in 2019 they set up decoy males in 40 areas of male bell seaweeds and 36 male Iberian sea urchins. They would then monitor the residents’ responses when a woman was around (see photo).
They used four decoys. One of them was falling and singing Iberá’s male otter. One thing was like a male bell-ringing seedeater. The other two had the appearance of one species and the song of the other.
If a resident man viewed a decoy as a competition it would be aggressive, by flying at him and grabbing it. And of course the men could tell the difference. They were very aggressive towards decoys that were similar to their own genre, much so towards decoys that combined features of both, and at least towards those which was similar to the other species. As these were not real birds, it must have been the color and the song.
The differences between songs may be of a cultural nature, and have occurred after their separation. But the differences in plums are clearly genetic. Moreover, they are so small that they may have occurred once as a result of unintentional crossbreeding, as similar genetic differences are found in different compounds across southern capuchino seawater. Also, what happened once seems to have happened often. So it seems clear that Ms. Turbeck has discovered the center of the machine with which this group has become so diverse. If so, she has helped write another page in that unpublished book, “The Real Origin of Species”. ■
This article appeared in the Science & Technology section of the print edition under the heading “Choice and determination”