Koalas are known for their unusual lifestyles. Now their genome has been sequenced for the first time, a breakthrough that is finally shedding some light on their strange way of life.
Koalas sleep for 22 hours per day and socialise very little. Their babies are born after spending just five weeks in the womb. And they live on an exclusive diet of eucalyptus leaves, which are toxic to most other mammals.
To find out how they do this, a team led by at the Australian Museum Research Institute in Sydney sequenced the complete koala genome, using DNA samples from three animals.
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The genome has already provided several insights into koala biology. For example, it has revealed special detoxification genes that allow the animals to feed on eucalyptus leaves without getting sick, as well as sophisticated taste and smell genes that help them to pick the most nutritious leaves. 鈥淭hat explains why you see koalas sniffing leaves before they eat them,鈥� says Johnson.
New clues about koalas from their genome:
- They have detoxification genes that allow them to eat poisonous eucalyptus leaves
- They have taste and smell genes that help them select the most nutritious leaves to eat
- Koala mothers鈥� milk contains antibacterial substances for preventing infections in babies
- Male koala semen induces ovulation in females to improve impregnation chances
The researchers also discovered genes that produce antibacterial substances in koala mothers鈥� milk. These may prevent infections in their tiny babies, which are born before they have developed immune systems.
In addition, the team identified genes that allow male koala semen to trigger ovulation in females. Since koalas don鈥檛 have much time for sex between naps, this trait may help to maximise their conception chances, says Johnson.
Saving the species
The researchers are now planning to use the koala genome to assist conservation efforts. This is crucial because koalas have been devastated by habitat loss and disease, especially the spread of chlamydia, says Johnson.
For example, the genome will help researchers to design better chlamydia vaccines, says Johnson. 鈥淲e鈥檝e been able to characterise koalas鈥� immune genes really well, so now we can see how they respond to different vaccines and see which one is most effective,鈥� she says.
The genome will also help to identify koala populations at risk of in-breeding, says Johnson. This is already known to be a problem in koalas in southern Australia, which have developed testicular abnormalities as a result of in-breeding. 鈥淣ow we can look at genes in different populations to see which ones we can cross-breed them with to increase genetic diversity,鈥� Johnson says.
Now that the koala genome is complete, Johnson and her team are embarking on a plan to sequence the genomes of all Australian mammals. This will show how they are related and assist efforts to protect endangered species.
The initiative will be part of a larger global push to decode the genomes of all animals and plants on Earth. To date, only a few hundred animals on Earth have had their genomes sequenced, including pandas, snow leopards and crocodiles. However, a global collaboration called the Earth BioGenome Project 鈥� a follow-up to the Human Genome Project 鈥� is aiming to sequence all of them in the next 10 years.
Journal reference: Nature Genetics, DOI: 10.1038/s41588-018-0153-5
