Scientists deep-freeze koala eggs and sperm to protect species from extinction

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Scientists in Australia are deep-freezing koala eggs and sperm as a "genetic backup" to save the wild population from future extinction.

The backup could be used to create healthy koala embryos through artificial insemination and in vitro fertilization (IVF), the researchers said in a statement . When koalas ( Phascolarctos cinereus ) die, unique traits and diverse genes that may help them adapt to changing environments are lost, but the new project offers a way to store this valuable material, the team said.

"Losing genetic diversity can weaken future generations and decreases the ability of the species to adapt to challenges," Andres Gambini , a reproductive biologist at the University of Queensland who is involved in the project, said in the statement. "This project will create a safe and systematic way to rescue and preserve koala spermatozoa and eggs to support future conservation programs."

Australia is facing a paradox with its koalas. In some regions of Queensland and New South Wales, koala populations have crashed by as much as 80% since the late 1990s due to deforestation, bushfires, drought and disease. This prompted the Australian government to change koalas' conservation status in their eastern range from "vulnerable" to "endangered" in 2022.

Meanwhile, in parts of southern Australia, koalas are overabundant. However, the places where koalas are currently thriving may not be able to support a booming population much longer, because the animals are overbrowsing and killing the trees they need to survive, recent research suggests.

To protect against koalas' decline, the scientists will freeze koala reproductive cells in liquid nitrogen (LN2), which has a boiling point of minus 321 degrees Fahrenheit (minus 196 degrees Celsius). This method would enable the team to cryopreserve the cells for several decades until they are needed, said Vincent Lynch , an evolutionary developmental biologist and associate professor of biological sciences at the University at Buffalo in New York.

Every year, many koalas are admitted to wildlife hospitals because of illness or injury and sadly, not all of them survive.

Andres Gambini, reproductive biologist at the University of Queensland

"I've successfully woken cells up that were frozen in LN2 a couple of decades ago," Lynch, who is not involved in the koala project, told Live Science in an email.

The sperm and eggs will be supplied by wildlife hospitals that will harvest sex cells from dead koalas or koalas that can no longer breed due to disease or trauma, according to the statement.

"Every year, many koalas are admitted to wildlife hospitals because of illness or injury and sadly, not all of them survive," Gambini said.

The researchers will then test the cells for Chlamydia pecorum , a highly contagious and deadly form of chlamydia . In koalas, this infection causes painful urinary tract infections, gastrointestinal issues, and conjunctivitis, which can lead to blindness. It can also cause infertility in females. C. pecorum is one of the main contributors to koalas' decline in recent years, with infertility driving a sharp reduction in the number of koala joeys being born. In the worst-affected populations, situated mostly in Queensland and New South Wales, almost 90% of koalas are infected with chlamydia .

If the reproductive cells contain C. pecorum , "we have the technology now to remove the infection from the samples," Steve Johnston , an associate professor of animal reproduction and captive husbandry at the University of Queensland who works on the koala project, said in the statement.

Andres Gambini and doctoral student Patricio Dandy Palacios, who participated in the project, want to preserve koala sex cells in liquid nitrogen. (Image credit: The University of Queensland) In 1998, Johnston was part of a research team at the University of Queensland that created the world's first koala joey born through artificial insemination . The new project also builds on a 2025 study , led by Gambini, that produced the first-ever IVF kangaroo embryos. (These did not result in live births; at the time, the scientists said that would take another decade.)

It's unclear how many sperm and egg cells the researchers plan on freezing, and it's hard to say how many cells they would need to ensure the survival of healthy koala populations, as the number of cells required is probably increasing with time, Lynch said. As koala populations shrink, genetic material is being lost at an accelerating pace, so the team will have to get more samples as time goes on to obtain the same amount of diversity.

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The project does not replace more traditional conservation approaches — such as habitat protection, disease management and population monitoring — but researchers cannot afford to wait until populations are smaller and genetic diversity is harder to recover, Gambini said.

Although conservationists are concerned about the fast rate of koalas' decline, "there is a chance" that scientists can save the species through cryopreservation, Lynch said.

"I support multipronged approaches like this," he said. "By preserving the environment with traditional conservation we allow re-introductions because the species have somewhere to live."