Koala genes could help scientists save these furry animals | Science News for Students

Koala genes could help scientists save these furry animals

Details show why koalas are picky eaters and why their numbers are dropping
Aug 13, 2018 — 6:45 am EST
a young koala rides piggyback on an adult koala hanging on a tree

Scientists have mapped koalas’ genetic code. They hope its lessons will save these animals.

Robyn Cox/Flickr (CC BY-SA 2.0)

What’s the news? Researchers have now pieced together the genetic instruction books of koalas. The furry marsupials [mar-SOOP-ee-uhls] join a growing collection of creatures with fully sequenced genomes. Marsupials are mammals with pouches and include kangaroos, wombats and opossums. Marsupial mothers feed their tiny babies in those pouches after they’re born. The large group of researchers published their koala findings online July 2 in Nature Genetics.

Why do we care? Lots of people love koalas. Many people travel to Australia each year to see them. Those visitors bring in $1.1 billion (in Australian dollars) every year, according to the government of New South Wales, a state in Australia. But fewer koalas are surviving in the wild. What is in their genome could give scientists ideas about how to save them.

Already, scientists knew that koalas in some groups have more similar genes than koalas in other groups. (Animal groups with more gene differences are usually healthier.) Hills, rivers and other barriers can keep groups of animals apart. Animals that can’t mix often with others often have more similar genes.

Scientists also already knew that Australia’s Brisbane Valley and the Clarence River separated koala groups. The new work shows that the Hunter Valley is a barrier, too. Knowing which groups can’t mix as easily will help biologists. They can design new ways to keep koala genomes diverse.

How many genes does a koala have? 26,558. That’s almost twice as many as researchers had counted before. New techniques allowed scientists find more genes.

Is that a lot? Yes, especially for an animal. It’s 5,000 more genes than are found in humans. But plants often have thousands more genes than animals do.

The koala’s genome also has more DNA than the human genome. DNA is made from chemical building blocks called base pairs. Humans have about 6.4 billion DNA base pairs, but koalas have about 7 billion base pairs.

a small koala sleeps while leaning on tree branches
Koalas spend more than half of their day sleeping. On average they travel just a few minutes each day.
Rebecca Johnson

What else does the study reveal? Koalas eat eucalyptus [YOU-kuh-lip-tuss]. These plants make toxic chemicals called terpenes [TUR-peens]. Eating eucalyptus would kill most other animals. But koalas can break down these chemicals. They use extra copies of special CYP2C genes. These extra genes make proteins that break down chemicals in koala livers. These proteins can chop terpenes into smaller pieces that dissolve in water. Then the koalas flush the chemicals out in their pee.

But those genes may have a downside, too. They may make it harder to treat a disease in koalas. This disease called chlamydia [kluh-MID-ee-uh] is caused by microbes. Scientists have medicines to treat the disease. But the proteins that help koalas break down terpenes can also tear apart the chemicals in the medicines. That keeps them from killing the microbes.

Scientists are also learning why koalas are such picky eaters. Even though there are more than 600 species of eucalyptus, koalas dine on only about 20. Koalas have more genes connected with detecting bitter tastes (a total of 24) than other Australian marsupials. That’s useful for avoiding terpenes and other toxic chemicals. Koalas also have a souped-up sense of smell. They have six times as many genes involved in sniffing as other marsupials do. Together, the smell and taste genes may help koalas choose a healthy diet. They need a balance of nutrients and fewer toxic chemicals.

Koalas also have two copies of a gene called aquaporin 5. That gene helps them seek out the juiciest plant leaves. That’s important because koalas don’t drink much. They get most of their water from eating leaves.

Fun facts: On average, koalas sleep more than 14 hours each day. They also rest up to eight hours while awake. Koalas spend most of their active time eating, from four to seven hours. They only travel, on average, four minutes each day.

Koala mothers’ milk may help protect the babies in their pouches. The milk has proteins that fight diseases caused by microbes and fungi.

Power Words

(for more about Power Words, click here)

base pairs     (in genetics) Sets of nucleotides that match up with each other on DNA or RNA. For DNA, adenine (A) matches up with thymine (T), and cytosine (C) matches up with guanine (G).

biology     The study of living things. The scientists who study them are known as biologists.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chlamydia     A sexually transmitted infection that is caused by the bacterium Chlamydia trachomatis. It can be spread through genital or oral sex, and often has no symptoms. If left untreated, however, it can cause infertility in women.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

dissolve     To turn a solid into a liquid and disperse it into that starting liquid. (For instance, sugar or salt crystals, which are solids, will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.)

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

eucalyptus     Several species of tall and aromatic trees found naturally only in Australia. Their wood is valued for timber. The oil found in the leaves has been used in medicine. And these trees are perhaps best known as the only thing adult koalas will eat.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genome     The complete set of genes or genetic material in a cell or an organism. The study of this genetic inheritance housed within cells is known as genomics.

liver     An organ of the body of animals with backbones that performs a number of important functions. It can store fat and sugar as energy, break down harmful substances for excretion by the body, and secrete bile, a greenish fluid released into the gut, where it helps digest fats and neutralize acids.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

marsupial     A type of mammal that carries its young for a period after birth in external pouches. There the developing babies have access to their mother’s nipples — and milk. Most of these species evolved in Australian and have especially long hind-legs. Examples of marsupials include kangaroos, opossums and koalas.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

taste     One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).

toxic     Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

Citation

Journal: R.N. Johnson et al. Adaptation and conservation insights from the koala genome. Nature Genetics. Published online July 2, 2018. doi:10.1038/s41588-018-0153-5.