Kingdom: Animalia
Phlyum: Chordata
Class: Mammalia
Order: Dasyuromorphia
Family: Dasyuridae
This is the Tasmanian Devil or Sarcophilu harrisii. They are found on the island of Tasmania, however they used to roam all of Australia. They were hunted on Tasmania up until they became protected in the 1940's. They were seen as a threat to the livestock, despite the fact that they are mainly carrion eaters, and rarely hunt. They are the largest carnivorous marsupial since the extinction of the "Tasmanian wolf" or Thylacine in the late 1930's.
The current populations of Tasmanian devils has been upgraded from vulnerable to endangered just this year. The decline in devil numbers has been drastic, with a estimated drop in numbers from 150,000 to 50,000-20,000 individuals in just ten years. The cause is a particularly virulent cancer which causes facial tumors on the devils. Once contracted, they die within a year to a year and a half.
The cancer can be spread from one devil to the next by contact (mainly bites). As matings frequently involve biting, and feeding is highly social (devils will call others to a meal) the disease has spread very easily and rapidly. Researchers have been working hard to figure out this issue, and they have found that because the devil's numbers were so reduced, that their immune system is not very genetically diverse (esp. MHC genes). Because of this cancerous cells from an infected individual are not rejected by a healthy individual because they are not considered foreign cells by the healthy individual's immune system [1, 2].
In an interesting response to this decreased life expectancy, the devil population is undergoing a shift in sexual maturity. Devils used to reach sexual maturity at two years of age. Now a high proportion of the population is sexually maturing at one year of age. This shift gives them a better chance to mate and produce offspring before they die [3].
4 comments:
I wonder though what the shift in reproductive age does for survivability of the offspring?
It is a really nasty looking cancer. I hope they find a cure or a way of fighting it soon.
this is rather interesting.
Has there ever been a case of disease being the cause of an extinction?
Is there any indication that the cause of the cancer is man-made? Or is nature just done with the Tasmanian Devil?
This is interesting to me in that there seems to be two natural forces at work shaping the Tasmanian devil, and whichever one wins out will determine whether or not the devil survives as a species.
Is there any indication that less aggressive devils are being less successful in reproducing or that feeding has become less social?
Eric:
I don't think it affects survivability of the offspring too much because females are essentially becoming semelparous. Since they only have one brood, they may shift more resources into that brood (rather than holding back for growth or subsequent broods). Of course since most of the offspring die at 2 from the disease any long-term effects may be difficult to seperate out.
Kate:
For your first question, I don't know. I do know that introduced parasites and diseases have caused local extintions, but if this could happen in the population where the parasite arose I don't know.
For the second question, they don't know the cause of DFTD although they have ruled out chemical causes. They have tried to trace the lineage and think it may have come from a single individual who's cell mutated and speard from there. What is imporatant to note is that this disease would not be so devastating if the population had not gone through a genetic bottle neck caused by humans killing off a majority of the population.
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