Koala genetics show how species can bounce back from bottlenecks
March 5, 2026
2 min reading
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Koalas show how species can bounce back from genetic bottlenecks
Scientists have discovered a potential route out of devastating genetic bottlenecks that could help these Australian animals, as well as many other vulnerable and threatened species.
Without interrupting their busy sleep schedule, Australia’s cute but temperamental koalas have overturned a genetic truism.
In short, the proliferation of some koala populations shows how bottlenecks, which occur when a species’ numbers suddenly decline, thereby reducing genetic diversity, do not necessarily condemn an animal to inbreeding and, ultimately, extinction. Species previously facing bottlenecks can bounce back, recovering a surprising amount of diversity.
“The hypothesis that a bottleneck would lead to eventual extinction is not set in stone,” says Rachel O’Neill, a genome biologist at the University of Connecticut, who was not involved in the new research.
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For the study, published March 5 in Science, The researchers searched the entire genome of 418 koalas from different populations to understand how the effective population size of different groups had changed over time. While the size of a population corresponds to the number of animals in a group, a effective Population size measures how the genetic diversity of these animals is distributed among individuals through sexual reproduction.
Researchers have discovered a trend they didn’t expect among koala populations in the Australian state of Victoria, where the animals have high rates of inbreeding and genetic deformation. Their effective population size exploded in the late 1800s due to the fur trade, creating an expected bottleneck. But surprisingly, scientists found that the effective size of koala populations in Victoria has increased over the past 40 generations, while those of koala populations in Queensland and New South Wales – which conservationists generally consider to be genetically healthier – have shown a marked decline.
“It still seems like they’re in bad shape, but if you dig deeper we see there’s a healing of the bottleneck,” says Collin Ahrens, study co-author and evolutionary biologist at independent research firm Cesar Australia.
This genetic recovery has occurred thanks to explosive population growth: in Victoria, koalas are now so numerous that their management involves trying to limit their numbers rather than increase them, notes Ahrens. What’s happening is that these populations have increased so dramatically that there have been many opportunities for mutations and even clustering of the limited genes retained during the bottleneck in different ways.
“Recombination reshuffles genetic variation,” explains Ahrens. “That’s really important and something that’s been very difficult to measure.”
What happened with Victorian koalas presents an interesting parallel to invasive species. Scientists have long known that invasive organisms can proliferate rapidly after just a few individuals are introduced into a new ecosystem they like. Instead of being haunted by inbreeding, they sometimes thrive genetically, to the detriment of the species around them.
The implications of this new research could extend far beyond koalas, given the number of species threatened by climate change and other anthropogenic pressures. “Right now we’re seeing a lot of anthropogenic declines, and I think their findings give hope to these populations,” says Caitlin Curry, a population geneticist at the San Diego Zoo Wildlife Alliance, who was not involved in the new research. “If we give them the right resources and tools to have some kind of rapid expansion, maybe that can also restore their evolutionary potential.” »
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