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Five cattle left on an isolated volcanic island gave rise to a large and resilient herd, in a story investigated by scientists for the relationship between genetics, rapid adaptation, and survival in an extreme environment in the southern Indian Ocean.
Five cattle left on Amsterdam Island, in the southern Indian Ocean, gave rise to a herd that reached about 2,000 animals after more than a century of isolation in a volcanic territory of only 55 km².
The trajectory was reconstructed through genetic analyses published in July 2024 in the scientific journal Molecular Biology and Evolution, which investigated how a population formed by few founders managed to sustain itself for so many generations.
Identified in the study by the acronym TAF, the population lived for more than 130 years without regular management, on a cold, humid island exposed to strong winds.
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According to the researchers, the group’s growth is associated with a combination of favorable genetic origin, environmental adaptation, and behavioral changes over the generations.
Origin of the herd on Amsterdam Island
The story began in 1871, when a French farmer attempted to establish a small colony on Amsterdam Island.
After the failure of the attempt, months later, part of the animals taken to the territory was left behind, among them five cattle that remained loose in the insular environment.
For decades, researchers debated whether other bulls and cows might have been introduced to the island later.
The question was relevant because a population with only five founders usually faces low genetic diversity, inbreeding, and a higher risk of disappearing in a few generations.
The genomic analysis helped reduce this uncertainty by identifying an extreme population bottleneck compatible with the historical records of 1871, about 22 generations before the collection of the samples evaluated.
According to the authors, the recent history of effective population size supports the hypothesis of a strong founder effect, reduced to five individuals at the end of the 19th century.
Based on these data, the case began to be treated by researchers as an example of successful colonization by a very small initial group.
Instead of disappearing, the herd grew, occupied part of the island, and maintained a large population for decades, even far from large continental masses and without the typical conditions of domestic breeding.
Bovine genetics explain survival
The study showed that the cattle on Amsterdam Island had an unusual genetic composition for a population formed by so few animals.
About 75% of the ancestry came from European taurine animals, close to the current Jersey breed, while the remaining 25% originated from zebus associated with the Indian Ocean.
This genetic mix is pointed out by researchers as one of the factors that help explain the survival of the animals in a considered hostile environment.
According to the study, the predominant European taurine ancestry may have functioned as a pre-adaptation to local conditions, as some of these cattle descended from populations accustomed to cold, humid, and windy climates.
The presence of zebu genes was also analyzed as a relevant element for the diversity inherited by the founders.
Although the initial group was small, the animals carried genetic variants from different lineages, which may have increased the capacity to respond to the pressures of isolation.
For the authors, the establishment of the TAF population can be explained, at least in part, by the pre-adaptation of the founders to the island’s climate.
The assessment does not eliminate the risks of such a restricted origin, but indicates that the genetic starting point of the herd gathered characteristics favorable to the environment found on Amsterdam Island.
Wild behavior emerged in a few generations
In addition to the genetic composition, scientists found signs of natural selection in regions associated with the nervous system and behavior.
These indications point to a process of feralization, when domestic animals begin to live and reproduce without human control, taking on characteristics more similar to those observed in wild populations.
Historical accounts cited in the study describe cattle as more aggressive, independent, and organized in complex social structures.
The organization included groups formed by females and young males, separate groupings of adult males, and seasonal gatherings related to the reproductive period.
According to Laurence Flori, a researcher at Inrae, the genomic results suggest that mutations already present in the founding animals played a role in the rapid adaptation of the herd to wild life.
The change would have occurred in a few generations, without relying on a long evolutionary scale, according to the interpretation presented by the study’s authors.
This point is highlighted in the research because it shows how a domesticated animal can quickly respond to an environment without fences, controlled feeding, or human protection.
On Amsterdam Island, natural pressure favored individuals with a greater ability to survive, move, compete, and reproduce in harsh environmental conditions.
Study challenges size reduction due to isolation
Another hypothesis analyzed by the authors involved the so-called insular dwarfism, a phenomenon in which large species can become smaller after long periods of isolation on islands.
This possibility was considered because the herd lived for more than a century in a limited area with restricted resources.
The investigation, however, found little evidence of significant selection for body size reduction.
According to the researchers, the cattle probably already descended from naturally smaller breeds, such as the Jersey and some zebus from the Indian Ocean, making the explanation by insular dwarfism unnecessary.
The conclusion alters the interpretation of the size of the animals in the TAF population.
In this scenario, the stature of the cattle would not necessarily be an adaptation acquired after arriving on the island, but a characteristic inherited from their ancestors.
With the genetic analysis, the authors sought to separate what may have been an effect of isolation from what was already part of the herd’s origin.
The result reinforces the importance of genomic data to evaluate changes in isolated populations, especially when historical records are limited or incomplete.
End of the Herd and Environmental Impact on the Island
Despite scientific interest, the cattle population was eliminated by 2010 due to environmental concerns recorded in conservation programs on the island.
The presence of cattle affected the vegetation and pressured important areas for native species, including the Amsterdam albatross, a threatened and endemic bird of the region.
The eradication was part of ecological restoration efforts in a territory marked by accumulated impacts since the arrival of humans and introduced species.
For local conservation, the removal of the cattle aimed to reduce habitat damage and allow the recovery of sensitive areas of the island.
Even with the elimination of the population, the study’s authors state that the herd represented a relevant scientific resource for understanding adaptation processes.
The TAF population gathered a history of colonization, survival, adaptation, and partial return to the wild from a minimum number of founders.
The case remains documented in genomic data and preserved samples, which allow the study of how domestic populations can carry genetic variants associated with rapid responses to new environments.
Even extinct, the herd of Amsterdam Island continues to be used as a scientific reference to investigate a unique episode of recent evolutionary history.
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