Twenty years ago, things seemed great for the Tasmanian devil.
The species had rebounded from several decades of intense persecution. It was originally believed that Tasmanian devils were a major threat to sheep, and from about 1830 to 1936, they were relentlessly hunted, trapped, and poisoned. Bounty systems were implemented, and their number did drop during that time period.
In 1936, Tasmania offered full protection to the Thylacine, which had become quite scarce in the wild. Because the devil was also quite uncommon, protection was offered to that species in 1941.
From 1941 until the 1960’s, the devils were allowed to exist without any sort of hunting pressure. And the numbers began to increase again. Occasionally, poisoning permits were issues to control devils in sheep production zones, but the animals were still officially protected.
By the 1970’s, there were concerns that the devils were overpopulated. In 1975, the population crashed, but it then rebounded. It continued to grow until 1987, when another crash happened. These sorts of boom and bust growth cycles exist in virtually all wildlife species, and it was assumed that the devils were developing along healthy lines.
Tasmania allowed permits to cull devils until the early 90’s.
Then in 1996, all hell broke loose for the devils. A contagious form of cancer was discovered. Called devil facial tumour [tumor] disease, it was originally believed to be caused virus. It is now founded to the result of a clone of malignant cells. It is transmitted with the devils fight over carcasses, which they are so famous for doing.
The devils are highly susceptible to this cancer. Since 1996, the devil population has crashed by 80 percent. Almost all of the loss is attributed to this disease. It is estimated that if the disease continues as it is now, the Tasmanian devil will be extinct in 25 years.
Why would the devils be so susceptible to this unusual cancer?
Well. It was always noted that devils were unusually susceptible to other forms of cancer. Cancer has always been a major cause of death in the populations that have rebounded since the devil was protected in 1941.
The reason for this susceptibility to cancer and to this particular form of cancer is really quite simple. Diversity in the genes in the MHC class I and II in Tasmanian devils is very low.
Devils have very low genetic diversity. There are certain reasons for this low diversity. One of these is that the Tasmanian devil in Tasmania is relict population. The animals were once found throughout Australia, but it is now represented only by population that became isolated on an island.
And this population experienced an extreme genetic bottleneck 10,000 years ago. The founding population that survived that bottleneck could have been as few as 500 individuals. This bottleneck has been exacerbated through intense persecution since Europeans arrived on the island, and because the MHC diversity was always compromised, the devils were often experiencing epidemics. It is thought that two population crashes that occurred in the first half of the twentieth century were the result of epidemics that rapidly spread through the genetically depauperate devils.
We are no longer talking about devils being overpopulated as they possibly were in the 1970’s and 80’s. We are now talking about possible extinction.
And it’s all because of inbreeding– inbreeding caused by natural causes 10,000 years ago and more recent inbreeding that has occurred because of intense persecution and habitat fragmentation.
This story should be a cautionary tale.
Just because a species has appeared to recover in numbers does not mean that all is well.
We have to pay attention to diversity within the MHC.
Many endangered species are in exactly the same position as the Tasmanian devil. Cheetahs are famously inbred, but thus far, no major disease has popped up that will kill them all. That does not mean that it won’t. It just means that it could easily happen.
And even our success stories might not be so successful.
In the US, we like to congratulate ourselves about the successful recovery of the northern elephant seal. In the early twentieth century, there could have been as few as 100 northern elephant seals left. The Mexican government protected the only surviving colony, and the US soon followed suit. Eventually, their numbers reached over 100,000 individuals. These are harem breeders, which means that only a few males produce offspring every generation. They suffer a definite popular sire effect, which wouldn’t be so bad if they weren’t already so inbred.
No bad diseases have popped up in these animals yet. However, one easily could.
As the devils have taught us, just because a species is particularly numerous does not mean it is not vulnerable. We have to pay attention to genetic diversity, especially in the MHC genes.
Unfortunately, many success stories in conserving wildlife species are likely to be similar to that of the Tasmanian devil. Genetic bottlenecks create small founder populations that may be able to recover in very large numbers, but because these populations have low genetic diversity, they are unable to survive epidemics.
This is why conservationist are so concerned with genetic diversity in all sorts of wild populations and within the zoo breeding programs. Genetic diversity is essential for endangered species to fully recover. Otherwise, they will always be vulnerable.
And if they are that vulnerable, how can we say that they have fully recovered? If one contagious disease can do this to the Tasmanian devil, what can another one do to the California condor, the Florida panther, or the giant panda?
Natural History 
Interesting that you should mention the Florida panther, which was ‘saved’ from inbreeding problems by crossing it with Texas populations. However, the population is still so small that it will need continual infusions of new blood to keep going. The devils and the panthers may have declined to the point of no return.
What would have been bad is some genetic study found that the Florida panther was so genetically distinct that it represents a unique species.
Then the Texas import thing would have been harder to justify.
One of the bad things about some of this genetic research is it gives taxonomists license to split.
And although there are cases of allowing some crossbreeding between species, it is generally verboten to species survival plans.
Right now, in Eastern North Carolina, the Fish and Wildlife Service is doing everything it can to keep coyotes from breeding with red wolves. They are trapping every coyote in that range they can find,
So it’s not much of a “recovered” species, if we have spend all of this time and energy trapping coyotes out of their range, just to keep them “pure.”
And they aren’t pure anyway. The ones that remain have all interbred with coyotes. They may even be a hybrid between the wolf and the coyote.
Here’s an interesting case: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009703
If that taxonomic status holds, that rhino might as well be considered extinct right now. There are only like 8 of them left that are “purebred.”
The Southern white rhino may MHC issues and may not be the success it appears.
It is actually hazard that I see coming from this desire to split up species.
Of course, if we decide a subspecies is a full species– like changing the the subpopulation of Indian pallipes wolves into Canis indica— then it is easier to get people to want to conserve them.
It can be a blessing or a curse.
Like dogs, it may come down to a choice: save the animal by crossing and making it genetically different, or lose the animal entirely.
I know the choice I’d make. But I’m not one to cling to ideals when they become completely impractical.
From what I’ve read of the Florida Panther efforts, the “crossbreeding” with the Texas females was quite successful, and the offspring have been much healthier and more vigorous. But that is really the least of their problems(although I think it was a good idea to do so)–their main problem is no habitat except for a very few animals, and no safe place for the young transients to disperse and set up their own territories–they usually just get hit on highways trying. One very large, vigorous male(positively identified as a “Florida Panther”–NOT an escaped or released captive, in other words) made it all the way to central Georgia before it was shot by a hunter, alas. Just a little further, and it would have reached the lower part of the Appalachian chain, and it would have had a good chance of surviving a full life span. This is why I WISH they would just capture these young transients, and transport them safely to the Southern Appalachians! Too many convoluted white-man politics involved there, though! But “panthers” ARE coming down in the North from Canada in the East, coming west across the Mississippi, and some may(or might already have!) make it up from Florida, and mixed with any surviving escaped/released captives(often with South American genetics!), we WILL have an established, reproducing population of “Eastern Panthers” in the East again, at least throughout the Appalachians and other large stretches of forestland–PLENTY of deer for them now, that’s for sure! And what a vigorous, diverse, and healthy set of genetic backgrounds will make up this population!
And the whole Red Wolf project trying to prevent “pure” Red Wolves from crossbreeding with coyotes is pointless and doomed to failure–eventually I’m sure they will just give up on that. This was tried in the Great Smokies Park in the Appalachians–same “problem”, and was eventually cancelled and some radio-collared “pure” Red Wolves were recaptured and removed–however, lots of “hybrids” remained, meaning the “coyotes” in the area have a nice chunk of Red wolf DNA in their genetics!! The “Red Wolf” has been recreated in the Northeast, as well, where the “coyotes” or “brush wolves”, as they are often called, have been tested and proven to have Gray Wolf DNA, and what-do-you know, they are amazingly similar to the “pure” Red Wolves of the Southeast in appearance, size, and habits! And they are also spreading Southward, undoubtedly to eventually mix with the Coyote X Red Wolf hybrids in the South! And this natural recreation(other than the Red Wolf releases in the Smokies and the coast of N. C.) cost zero tax payer dollars! And the East will have a “Wolf” again, better suited to survive here, as the original Red Wolves were before the European invasion! Not being a purist at heart, I’m all for it–Nature WILL find a way!
and the same applies to tigers. Do you save “tigers” or do you let them all die so you can say you tried to save “Siberian tigers” seperate from “Bengal tigers”? We act as if diversification is this cut and dried thing — a “species” must be inviolate if we can identify it by unique DNA. No outbreeding then allowed. It’s stupid. If they came from a “most common recent ancestor”, then it is better to combine them again if the alternative is to let them die. For Tazie devils, there’s nothing there to breed them to, but it’s likely the Andean and California condors would be able to produce viable offspring. It’s likely the Indian and African lions can too. And Florida “panthers” can certainly have some of those currently living in California. At this point, virtually no tetrapod on the planet will survive without at least some human assistance in terms of setting aside areas to live and numbers for breeding. The only alternative to human management is reduction in human population, and I don’t see that happening any time soon.
Peggy Richter.
Couldn’t some judicious crossbreeding of the various Cheetah subspecies be done as well? Would that not help the diversity problems they have?
From what I read, the Cheetah are so inbred that only an outcross and breed back program could save them. Possibly with the serval IF that could be done. But it would take, money, time, and habitat to do it in wild populations, and a person with a strong indepenent streak to do it in a zoo.
All five subspecies are really that closely related to each other?
Yeah.
Those subspecies might be only two: one in Africa and one in Iran.
The only way to increase genetic diversity would be to do an outcross with another species– the cougar, not the serval.
I don’t know if this is technically possible and a lot of the offspring– if any are born– would fertility issues.