In 1871 a farmer abandoned five cows to their fate on a remote island. Against all odds, they colonized the island

A Frenchman goes and releases five cows on a small island where Christ lost his lighter. It sounds like a joke, but it’s true: it happened in 1871, the Frenchman was a farmer on the island of Réunion and the destination island is called Amsterdam, it is only 55 square kilometers and is in the southern Indian Ocean. What happened next will surprise you because, well, it also left the scientific community in awe, as demonstrated by the quintet’s different studies.

Introducing an exotic species into new habitats is a box of surprises that usually ends up regular: ask the crabs that were native when the American crab arrived, the fish that were in the Ebro before the catfish or the mythical Pitiusas lizard, which has found in the invasive snakes that you may encounter swimming a new and ferocious predator in the waters of the Balearic Islands. But hey, there are only five cows and the island is very small, right?

Well yes: biology maintains that for a foreign population to establish itself successfully it is necessary that there be a sufficient number of initial individuals to guarantee genetic diversity and avoid extinction due to inbreeding. But there are also exceptions: genetic invasion paradoxwhere tiny populations manage to prosper in a surprising way. This is the case of our beef quintet.

Once upon a time there were five cows abandoned to their fate.. In reality, the farmer came to the island with other people with the idea of ​​staying, but in the end it didn’t work out and five cows is not the lightest carry-on luggage in the world, so they stayed there. The subantarctic conditions were harsh and genetically there was a bottleneck, but the animals not only survived but reproduced successfully and happily.

In fact, the population grew exponentially over the decades, reaching historical peaks of up to 2,000 individuals: yes, Amsterdam Island became the island of cows and is also one of the few cases recorded worldwide of completely feral cows.

Why is it important. Because it challenges one of the central principles of conservation biology: the minimum viable population sizewhich establishes that below a threshold a population has a high probability of becoming extinct due to genetic drift, inbreeding and accumulation of mutations (the figure depends on the species and the model, but classical models point to hundreds or even thousands of individuals). Understanding these processes provides theoretical tools to better manage invasive species and the conservation of genetic reservoirs.

That five cows founded a viable population for more than a century is, in that context, an anomaly that science could not ignore. In addition, it offers a valuable perspective on the speed at which evolutionary and behavioral changes can occur in a mammal when the bond of domestication is broken.

Context. Amsterdam Island is part of the French Southern and Antarctic Lands. We are talking about an isolated island ecosystem where there were neither large predators nor other large competing herbivores, so what is a bit of cold and wind. This initial condition made it possible for livestock to spread, although in the long run overpopulation ended up causing serious damage to the native flora and threatening endemic birds.

Under the microscope, the samples analyzed revealed that there was a mixed ancestry: a combination of mainly European bullfighting cattle, but also Indian Ocean zebu. After analyzing the climate, they found that the conditions were not too different from other known scenarios in old Europe, such as Brittany, so the cows were not starting from scratch: your preadaptation to the climate cushioned the impact to the new habitat.

What really happened. Some initial research they pointed to the fact that the cattle suffered from accelerated “island dwarfism” to adapt to the scarcity of resources, although genomic analyzes ruled it out: if these island cows were small it was simply due to direct inheritance from their ancestors, the also relatively small zebus of Madagascar and Jersey breed.

The real change occurred in his behavior: the study identified that the genes that evolved the fastest were related to the nervous system, which the authors interpret as the genomic signature of feralization: the ability to organize in herds, reactivate alert responses and survive without human intervention.

Yes, but. What this quintet of cows achieved was a feat of survival, but at what price: the genetic analysis showed a moderate reduction in their genetic diversity and a slight accumulation of potentially harmful variants, something to be expected after such a severe bottleneck, although without reaching the critical levels associated with populations at risk of extinction.

Furthermore, the story had a sad and controversial ending: considering the damage they caused to the island’s environment, the authorities decided to sacrifice all the cows in 2010 and this unique experiment and its extraordinary and particular genetic lineage came to an end.

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Cover | Copernicus Sentinel 2021 via Wikimedia and Iga Palacz