Look out for a surprise! This week’s column ventures into territory likely unknown to most readers. There is the animal, first: the bush hog. Anyone who has ever heard of this cousin of the wild boar and the warthog, raise your finger! In Africa, this suidae is nevertheless extremely common. Bushmeat lovers love its tasty flesh. The peasants appreciate him much less, who curse his raids on crops. In Madagascar, it occupies an even more important place. Since the disappearance of large terrestrial lemurs and pygmy hippos centuries ago, it has held the title of largest mammal on the island. But its arrival in this territory of the Indian Ocean has always been a mystery, on a par with another mystery, that of the landing of humans.
Curiously, Madagascar is the island-continent (resulting from a tectonic detachment, as opposed to volcanic islands) most recently colonized. While it is only separated from Africa by the 400 kilometers of the Mozambique Channel, it was only inhabited by humans “the day before yesterday”, researchers like to say. In other words, a few thousand years ago: eleven thousand years, say the most daring, from supposed traces of butchery on bird bones; only two thousand to four thousand years, according to most scientists. In any case, we are far, very far from the sixty thousand years of human colonization documented in Australia, for example.
An article, published Wednesday January 3 in the journal Nature Communications, sheds light on these two mysteries. The international team, led by Rasmus Heller, from the University of Copenhagen, first wanted to understand the evolutionary history of the bush pig. Or rather bush pigs. Because, since 1993, the species has been split into two, with Potamochoerus porcus in the west and center, characterized by its red color; to the south and east, Potamochoerus larvatus, grayer, stockier.
“Speciation is not complete.”
The researchers analyzed the genomes of sixty-seven specimens from ten countries. It appears that the two populations began to diverge around three hundred thousand years ago, at the same time as other large animals (buffalo, lion, elephant, baboon). Started, but not really finished. “Genetic differentiation remains modest,” insists Rasmus Heller. And we see gene flow between the two populations. » Recent observations, in western Uganda, seem to attest that between P. porcus and P. larvatus we don’t just look each other in the eye. Thus, for Rasmus Heller, “speciation is not complete”.
The other big piece of information came from the twenty-six genomes of Madagascar bushpigs. When and how did their ancestors land on the island? Alone, enjoying drifting “rafts”? Or in humans’ luggage? “Our analysis makes the first hypothesis very unlikely,” explains Jordi Salmona, researcher at the Research Institute for Development (Toulouse), who focused on the Malagasy part of the project. A demographic bottleneck dating back one thousand to five thousand years has been revealed. “We interpret it as a founder effect of this population,” specifies the geneticist. Bush hogs would therefore have set foot on the island at the same time as the first humans or just after.
Not just any ones, anyway. Researchers rather favored an arrival in the luggage of Austronesian navigators, coming from South Asia via the Horn of Africa. However, the analysis is clear: it is not to their cousins in Tanzania that the bush pigs of Madagascar appear to be closest, but to those of Zimbabwe and South Africa. Everything therefore suggests that they were introduced by the Bantu populations, the other major demographic source of Madagascar.
To those who still doubted it, migration is a human constant. She left her traces everywhere. Even in the genome of bush pigs.