Koalas, Phascolarctos cinereus, are a marsupial native to Australia. They are habitat specialists, feeding almost solely on eucalyptus leaves. Observations over recent years have shown that koala populations are diminishing at an alarming rate. Many factors endanger the continued existence of the koala, such as habitat loss, climate change, and hunting. Koalas have an extra burden to bear in that they are extremely susceptible to disease, in particular chlamydia. Once infected, a chlamydia carrying koala may develop blindness, infertility, and other disorders that are a barrier to successful reproduction.
Research suggests that the high chlamydia susceptibility seen among koalas is due to a particular virus, which is transmitted at birth and possibly during mating or fighting. This virus acts to lower a koala's immune system.
Recent research using mRNA comparisons confirm that current koala populations have an extremely low genetic diversity. Koalas populations were drastically reduced in the mid 1800s, when European settlers generated a demand for their fur. While it would seem reasonable to assume that current genetic diversity is a remnant of this hunting period, researchers now believe that koalas are still feeling the effects of some event during the pleistocene, when the only other species of koala went extinct.
http://www.sciencedaily.com/releases/2012/10/121023204636.htm
http://www.nytimes.com/2012/02/21/science/queensland-koalas-hit-by-chlamydia-infections.html?_r=0
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