The number of koalas in most parts of Australia has declined precipitously over the past few decades , as the eucalyptus forests they inhabit have been shaved down to make way for development and devastating diseases spread. Rebecca Johnson , a conservation geneticist at the Australian Museum in Sydney and the lead author of the study published today in Nature Genetics , was constantly getting calls from state officials and development companies asking for her advice about how help preserve healthy, genetically diverse koala populations around the country.
So she rounded up a team of specialists from around the world who slowly assembled the pieces of the genetic puzzle. Cute, and also very strange. Koalas survive on stringy eucalyptus leaves, which are filled with toxic molecules that render the plant inedible to basically every other living thing. Koalas, though, evolved the ability to flush the toxins out quickly, so they can eat their way through pounds of leaves each day without getting sick.
The leaves contain so few calories, however, that they spend 22 hours of the day resting or sleeping. Johnson and her team found that the part of the koala genome that codes for detoxifying proteins is about twice as big as in other mammals or humans.
At some point in the deep past, the researchers hypothesize, that section must have accidentally duplicated itself. The team also learned something about how koalas pick their food. For years, researchers have watched koalas sniff at leaves and wondered why they chose to eat some but throw others away. They suspected that the koalas were able to somehow sense how toxic or nutritious each leaf was based its smell.
Koalas are really good at getting rid of poisonous plant molecules, but the system that flushes those out also clears many medicines out of their systems very, very quickly—many times faster than humans. And antibiotics used to treat some diseases mess with their gut microbiome , interfering with their ability to break down eucalyptus leaves, slowly causing them to starve.
Many researchers have spent years trying to develop a vaccine that could prevent koala chlamydia. Koalas also suffer from a retrovirus, similar to HIV, that weakens their immune systems and makes them even more susceptible to diseases like chlamydia or cancer.
Sometimes, those retroviruses slip themselves quietly into the genetic code. The researchers found that retroviruses had inserted themselves dozens of times over koalas' evolutionary history, but the sneak-attacks continue today. At this point, all of the koalas tested in Queensland have some version of the retrovirus. But some of the modern strains are more destructive than the ancient ones. In Australia there are over types of eucalypts, but Koalas will not eat a large proportion of these.
Within a particular area, as few as one, and generally no more than two or three species of eucalypt will be regularly browsed. Different species of eucalypts grow in different parts of Australia, so a Koala in Victoria would have a very different diet from one in Queensland.
Also, just think how boring it would be to eat the same thing every day. Koalas like a change, too, and sometimes they will eat from other trees such as wattle, tea tree or paperbark.
If you live in a koala area, find out what type of eucalyptus the koalas in your area like to eat. Some people think that koalas sleep a lot because they get drunk on the eucalyptus oil in gum leaves. Koalas sleep or rest for up to 22 hours each day because their bodies need a lot of energy to digest the gum leaves and when they are sleeping they save energy.
Very few animals can survive on a diet of gum leaves. They are very fibrous and low in nutrition, and this is why they take a lot of energy to digest. As well, to almost all other animals they are poisonous. However, koalas are especially adapted to eat this diet. They have a special part in their intestine, called a caecum pronounced see-kum , which goes off from their main intestine and has a blind end.
It is very long and broader than the rest of the intestine and contains millions of micro-organisms tiny organisms that break down the gumleaves so they are easier to absorb. There is water in the gumleaves, too, so that koalas rarely need to drink. Koala teeth are especially adapted for their gumleaf diet. Their sharp front teeth nip the leaves from the tree and their back teeth are shaped for cutting and grinding the leaves to extract the most nourishment.
An adult koala eats between to grams of leaves each day. They rely on a slow metabolism and conservation of energy through sleep and resting. Koalas generally feed for two to four hours every day, usually in the evening, or in drier climates, in the morning to collect moisture from the dew on leaves. Koalas generally show a preference for younger foliage, as it usually contains more nitrogen, moisture, and sugars than older, mature foliage.
The palatability of certain species depends a lot on the available nutrient in the soil, as trees growing in poor nutrient areas tend to produce compounds in their leaves that deter feeding as a protection for their foliage. Koalas are relatively sedentary and localised in their movement.
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