Newly Mapped Koala Genome Unlocks Secrets of Marsupial’s Diet, Susceptibility to Chlamydia

The cuddly creatures can survive on a diet of high-toxin eucalyptus leaves thanks to detoxifying genes

Koala populations are expected to drop by 50 percent over the next 20 years Flickr / Creative Commons

Koalas are some of the most beloved creatures in the animal kingdom—with their soft gray fur and cherubic faces, the marsupials exude enough charm to sustain a $1.1 billion tourism industry in their home country of Australia. But beyond these fuzzy exteriors, koalas hide an array of unusual characteristics, from a eucalyptus-based diet (the leaves are poisonous to most other mammals) to a deadly susceptibility to chlamydia.

Now, a consortium of 54 scientists from 29 institutions has assembled the first complete koala genome, unlocking some of the animal’s most enigmatic secrets. The team’s findings, published yesterday in Nature Genetics, map out all 26,000 genes in the koala genome. Comparatively, Matt McGrath notes for the BBC, humans have about 20,000 genes.

Rebecca Johnson, founder of the Australian Centre for Wildlife Genomics and lead author of the paper, tells the Los Angeles Times’ Deborah Netburn that scientists hope to use the genome to ensure the koala’s long-term survival.

“The ultimate goal is that we won’t have to use ‘emergency room conservation’ and rescue them from the brink of extinction,” Johnson says. “Now we have a really good understanding of the koala genome, and we are in a fantastic position to use that knowledge to help us manage them.”

Current estimates of Australia’s koala population range from 100,000 to 600,000, Johnson tells Popular Science’s Kat Eschner. That may sound like a lot, but the Australian Museum expects these numbers to decline by 50 percent in the next 20 years, Netburn reports.

Two of the major issues precipitating this decline are habitat destruction and an ongoing chlamydia epidemic. Because koalas survive on a diet of eucalyptus leaves, they require specific kinds of habitats—according to Science News’ Tina Hesman Saey, koalas will only eat about 20 of more than 600 species of eucalyptus.

Although the high level of toxins found in eucalyptus would prove fatal to most animals, the newly mapped genome reveals that koalas have extra copies of detoxifying genes. The critters’ picky eating tendencies also come down to genes: Eschner writes that koalas have a strong sense of smell and taste, which allows them to evaluate leaves based on their bitterness and water content, choosing the juiciest ones.

According to Netburn, the koala’s detoxification genes also mean it metabolizes medications such as anti-chlamydia antibiotics faster than most animals, which helps to explain why the disease has been so hard to treat in koalas. Whereas humans might benefit from a single dose of medicine, koalas would require a daily dose for 30 to 45 days. There are additional problems associated with antibiotics, National Geographic’s Alejandra Borunda reports—in some cases, the medicines have reduced koalas’ ability to break down eucalyptus leaves, thereby rendering them unable to digest their main food source.

Chlamydia, a bacterial disease that has ravaged koala populations in Queensland and New South Wales, produces a number of devastating effects. McGrath writes that victims can experience blindness, infertility and “dirty tail,” a painful urinary tract inflammation.

Adult koalas get chlamydia the same way that humans do, reports Mindy Weisberger at LiveScience: through sexual transmission. Immature koalas can become infected when they eat pap, a special kind of feces excreted by koala moms to nourish their joeys.

Although koalas appear to be plagued by a disproportionate number of environmental and genetic issues, the new genome offers hope to koala conservationists worldwide.

“All our efforts in the whole koala research community to develop a [chlamydia] vaccine ... [have] been limited by the fact that we don’t know enough about their immune system,” Willa Huston, a microbiologist at the University of Technology Sydney, tells Borunda. “Now that we have an understanding of the thousands of genes involved in the immune response, we can use evidence and science to craft a targeted vaccine.”

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