Wednesday, 6 January 2016

The devil's away

Sarcophilus harrisii is about as cute as your average dog or cat [and R] but has had a bad press in Tasmania, especially in livestock country, where it goes by the common name Tasmanian Devil.  Since Thylacinus cynocephalus the Thylacine shot to extinction 80 years ago, Sarcophilus harrisii has been the world's largest carnivorous marsupial, which is to say not very large. But it has the distinction of having the most powerful jaw muscles of any extant mammal, which it uses to crush bone and rend sinew. When you look at them in captivity being hand-fed by the staff, you can't really understand why anyone would take against them.  But I guess Australian farmers would give you a different story of dead lambs. The 'Harris' who first described and named the species, was George P.R. Harris a short-lived and perhaps dissolute government surveyor who picked the site on which Hobart was built.

Sarcophilus used to be the Australian Devil because fossil evidence indicates that it was distributed all over continental Australia in the Pleistocene. But, with the coming of man and dingos, the smaller carnivore has been in retreat and has been confined to Tasmania for the last 3000 years. Note: current taxonomy lumps dingos, domestic dogs and wolves into the same species Canis lupus.  It seems that Sarcophilus is not long for this world and, in this instance, humans are only partly to blame. It's true that they attracted a bounty for hunters in the 19thC but they have been protected by law since 1941. Some believe that Sarcophilus has been instrumental in limiting the extent to which European red foxes Vulpes vulpes have invaded Tasmania. Foxes are a decided pest elsewhere in Australia; so that's a good reason for wanting to Save the Tasmanian Devil; t-shirts; mugs.

The main threat to Sarcophilus over the last 20 years is a foul transmissible cancer called DFTD - devil facial tumour disease [picture for the well 'ard].  This is presumably some sort of virus but is associated with abnormal chromosome count. It was first observed 20 years ago and can spread from animal to animal by contact.  The tumours blurf up in and around the mouth as weeping sores that interfere with feeding, and presumably make the wee things feel real crappy and so soon enough kill the poor creatures. Estimates of the effect this is having on numbers vary wildly between 20% and 80% mortality and there are some regions of Tasmania where the disease has not yet been observed.  Anyway, between DFTD, roadkill and trigger-happy farmers the population of the species has declined 60% in the last 10 years.  Sarcophilus does not breed well in captivity but DNA sequencing has allowed scientists to sequester 98% of the genetic variablity in zoos; with the intention of returning the species to the wild after the virus has played itself out. Keeping this one species on the planet is estimated to have an interventionist price-tag of US$11million. Not as cute a pandas Ailuropoda melanoleuca? or Orang utans Pongo abelii? there are 5000 species of mammal we can't save them all.

Now IFLS reports that a second transmissible tumour has been isolated from Sarcophilus which also causes facial tumours but appears to be genetically distinct.  That's weird because transmissible cancers are really rare in any species and to have two infecting one small marsupial carnivore makes you think that there may be a defect in their immune system. "To have one tumour may be regarded as a misfortune; to have two tumours sounds like carelessness."

Ah go on then: list ye well tae The De'il's Awa' Wi' The Exciseman by Ewan MacColl

No comments:

Post a Comment