ÃÈÃÃÉçÇø

Since the late 1800s, koala numbers have declined dramatically, but it is not only their numbers that are disappearing. A recent analysis has shown that the variation of genes within koalas has also decreased, with some traits present in historical specimens that are now absent in today's koala populations.

Researchers compared 25 modern koala genomes with those from 37 historical specimens to see how genetic diversity has changed in the marsupials over time.

Ancient DNA was extracted from the older specimens, some of which are cared for at the Natural History Museum in London, and were collected before the most recent species decline began towards the end of the nineteenth century.

Professor Ian Barnes, who studies ancient DNA at the Natural History Museum and was involved in the study, says, "It is important to compare modern DNA with historical data because if you only looked at modern data, you might notice a group has very low genetic diversity and presume that's really bad. But what we have found in some species is that you can go back thousands of years, and they've always had low genetic diversity."

"But if you look at museum specimens and can see that genetic diversity was high 100 years ago and is now really low, and that's not a good sign. The group is not accustomed to having that low genetic diversity, and it also might be because of inbreeding due to the population size getting smaller."

The results of the analysis have been in the journal Molecular Biology and Evolution.

Why is loss of genetic diversity bad for a species?

Genetic diversity is the variation that occurs within the genes of a species.

DNA exists within structures called chromosomes. For mammals, chromosomes typically come in pairs, with one half of the pair inherited from each parent. If the parents are genetically unrelated, there is a higher chance that they will have a different version of a gene at a particular location on the chromosome.

This is known as heterozygosity. If an individual has a high heterozygosity, they have a lot of genetic variability.

In contrast, homozygosity is where an individual has two identical versions of the same gene. The closer an individual's parents are genetically, the more homozygosity they will have and the more inbred the offspring will be.

This means that as populations get smaller and inbreeding increases, it causes a decrease in genetic diversity and can make a species less resilient to environmental disturbance.

"Having low genetic diversity is often associated with an inability to deal with environmental change," says Ian. "So if you've got two different copies of a gene, one from each parent, it gives you some degree of adaptability."

"For instance, if you need to be able to cope with increased temperature, you might find that the one copy of a gene that you got from your dad is good at dealing with lower temperature. The other one from your mom is better at dealing with high temperature. So it just gives you more tools in your toolkit to help you adapt to a changing environment or the introduction of new diseases."

A recent study found that loss of genetic diversity is becoming a real problem for species across the world. This is such a significant issue that maintaining genetic diversity formed a key component of one of the goals agreed upon at the biodiversity conference COP15 in 2022.

How can we increase the genetic diversity of koalas?

Koala populations declined dramatically from the 1890s into the early 1900s due to a surge in hunting for their pelts to supply the local and international fur trade, with reports showing tens of thousands of pelts arriving at the docks of London every year. At its peak, in 1924 an estimated 2 million koalas may have been killed in Queensland alone.

Although the fur trade was stopped in the 1930s, many koala populations had already been driven to extinction.

The loss of their habitat threatened the marsupials throughout the twentieth century and remains one of the most significant pressures on the species today. Disease, vehicle collisions and record-breaking numbers of bushfires have also contributed to their decline in more recent times.

As climate change and habitat loss continue to fragment surviving koala populations, active conservation management will likely become even more necessary.

Understanding more about the loss of genetic diversity can play a part in helping to focus conservation efforts. If done correctly, translocations could be a means to help prevent inbreeding and preserve their diversity.

"Our study recognizes four genetically separate populations of koala," says Ian. "These populations don't interbreed heavily, and are likely to be adapted to the area they live in."

"We therefore can't treat all koalas as being from a single population and do large-scale translocations. For instance, the populations in Queensland might have genes that make them better at dealing with a different environment to those further south in Victoria."

With this better understanding of koala genetics, the scientists hope that it will help conservationists to create a more resilient plan to help save the iconic marsupials from slipping into extinction.

This story is republished courtesy of Natural History Museum. Read the original story .