Tuesday, January 11, 2011

Eucalyptus kybeanensis--Kybean Mallee Ash

This is one of my favorite trees at the UC Botanical Garden. I love the way the trunks twist and the bark shreds and hangs. So melodramatic! I can almost hear the organs...

An Australian marsupial, the koala, has a very close relationship with eucalyptus. In fact, they eat very little else. It is a difficult diet, because it is low in protein, mostly indigestible, and contains many toxins. I can't imagine eating eucalyptus. Too strong!

Any diet has its pros and cons. For the koala, it has little competition for the eucalyptus, no other animals eat it. So it is easy to find enough food without having to fight for it. But they have to put so much energy into dealing with the toxic leaves, they don't have much left over to develop any brain power. Almost half of the skull is filled with cerebrospinal fluid. No other mammals have such a reduced brain.

The digestive tract of the koala is has adapted to handle the strange diet. The hind gut is enlarges and harbors special bacteria to ferment the leaves. The mother passes these bacteria to her offspring when she excretes pap for them to eat. The pap is soft, runny droppings that the mother produces. It is one of the first things koala babies eat when they are being weaned. In fact, they lick it from her anus while they are leaning out of the downward-facing pouch. It seem disgusting, but if they didn't ingest the bacteria from their mom, they wouldn't survive.

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