Sunday, April 5, 2009

The Wolves of Isle Royale - The Implications of the Transitional Vertebrae Findings

The canine genetics lists and Terrierman are all a twitter about the finding of transitional vertebrae in the inbred population of wolves that live on the Isle Royale in Lake Superior. Terrierman blogs in his typical sensationalistic style that Inbred Wolves Live with Pain (April 4, 2009). Oh, the horror of inbreeding! Once again Terrierman speaks from an uninformed and unresearched position.

Background Information:

Approximately 24 wolves (up by one from last year) and approximately 520 moose (down by 650 from last year) live on the Isle Royale that is situated in Lake Superior. The Isle Royale is just 50 miles long and 8 miles wide.

The moose population originated with moose that are believed to have swam to the island in the 1900's. The wolf population is believed to have stemmed from wolves that crossed the ice from Minnesota or Ontario around the year 1950.

The population of moose and wolves fluctuate from year to year. The moose peaked at 2,445 in 1995. The 2007 moose survey of 385 has been the lowest numbers recorded. The number of wolves has ranged from a low just 11 in 1993 (following the introduction of parvovirus by a dog) to a high of 50 in 1980. The approximately 24 wolves currently on the island are divided into three packs.

Moose kills comprise 90% of the wolves diets. They hunt and kill moose in packs of about 6 or 7 wolves. Bringing down a moose is no easy task even for 6 to 7 wolves, it requires expending considerable energy, and the wolves are frequently injured. Most have suffered broken ribs from being kicked by moose. The body of one wolf that was retrieved by researchers was found to have broken ribs, and bruising and bleeding in the lung area, sustained most likely from being kicked by a moose that it was attacking.

The main causes of death for the wolves of Isle Royale include: (1) lack of food, and (2) being killed by other wolves in conflict over food.

The Isle Royale moose can live to 17 years of age, but most die before 9 years of age. They are plagued by winter ticks which feed on their blood and cause hair loss and just make life miserable for the moose.

Isle Royale wolf pups that manage to survive to 6 or 7 months of age, tend to live on average to 3 or 4 years of age. Some years none of the pups survive. An alpha wolf may survive to 9 or 10 years of age.

The wolves of Isle Royale walk approximately 30 miles a day.

Researchers who track the populations of moose and wolves on Isle Royale are concerned about the arthritic spines (spondylosis?) and transitional vertebrae that have been found in 58% of the skeletal remains of wolves found on the island since 1993.

Read here about a witnessed moose kill involving seven wolves

Now I ask you, after reading this, did you get a picture of crippled up wolves in agony?

Of course not!

And there is good reason to believe that the transitional vertebrae findings in the wolves of Isle Royale are not causing pain or mobility issues.

Why do I say that?

Because transitional vertebrae and spondylosis are usually an incidental finding in dogs for the most part and typically do not present with clinical signs requiring treatment.

Why would it be any different for wolves, especially considering their short life span (3 to 4 years) in the wild?

Quick facts about spondylosis:

  • Found in 70% of dogs
  • Occurs in mixed bred and purebred dogs
  • Typically an incidental finding when xraying for some other reason
  • Rarely produces clinical signs
  • OFA does not see as a reason to remove a dog from a breeding program
  • Also occurs in cats (68%)

    • Quick facts about transitional vertebrae:
      • Typically an incidental finding when xraying for some other reason
      • Rarely produces clinical signs
      • OFA does not see as a reason to remove a dog from a breeding program
      • Can be associated with hip dysplasia
      • Frequent in cats and rarely presents with clinical signs

      What do veterinary radiologists have to say about transitional vertebrae and spondylosis?

      From Small Animal Radiology and Ultrasonography: A Diagnostic Atlas and Text by Ronald L. Burk, Daniel A. Feeney, Norman Ackerman (2003):

      "Spondylosis deformans is the most common degenerative disease that affects the spinal column. This produces a partial or complete bony bridge between the caudal aspect on one vertebral body and the cranial aspect of the adjacent vertebral body. The body proliferation, although frequently present on the ventral and lateral surfaces of the vertebral bodies, rarely is present on the dorsal portion and therefore rarely encroaches upon the spinal cord or on the nerve root. Thus spondylosis almost never has clinical ramifications except for pain in "nearly" bridged vertebrae. In rare cases the amount of spondylosis may become extensive. Bridging spondylosis involving fore or more contiguous vertebrae has been termed diffuse spinal idiopathic hyperostosis (DISH). Close scrutiny of these animals will reveal stiffness in some individuals. Spondylosis may be seen at necropsy in dogs as young as 6 months of age but is usually a disease of older large breed dogs. The ossification may start from one vertebrae and grow toward the other, may start on both and meet in the middle, may start in teh middle and progress in both directions, or may have any combination of these variations. Spondylosis may result in complete spinal fusion. Some mechanical interference with normal activity may results, but in most cases the bony lesion doesn not produce clinical signs. Narrowing of the intervertebral disc space maby occur secondary to spondylosis, but in most cases the disc is not prolapsed. Spondylosis may also occur secondary to chronic disc prolapse. The distinction between these two conditions usually is based on the amount of spondylosis that is present. If only one disc space is affected and there is no evidence of spondylosis at other sites, then the lesion most likely is primary disc degeneration with secondary spondylosis. If there is extensive spondylosis with only one narrowed disc space, then the lesion most likely is primary spondylosis deformans with secondary disc degeneration. If clinical signs are present. a myelogram is needed to document or rule out disc prolapse."

      From Exercises in veterinary radiology: spinal disease by Joe P. Morgan, Cleta Sue Bailey (2000):

      "Many of the dogs with a transitional vertebrae have concurrent hip dysplasia. If the pelvic attachment in these dogs caused angulation and/or pelvic rotation, an assymetrical arthrosis results. The resulting degree of femoral head subluxation and secondary osteoarthrosis is greater in the hip in which the dorsal acetabular coverage is decreased."

      "Transitional vertebrae in the cat are frequent and have a similar appearance to what is seen in the dog, however, they are rarely associated with a clinical problem. This may be a result of the cat's smaller size or may relate to their physical activities."

      What does the Orthopedic Foundation for Animals (OFA) say about transitional vertebrae and spondyosis?

      "Transitional vertebra is an incidental radiographic finding noted during the evaluation process. Transitional vertebrae are a congenital malformation of the spine that occurs at the junctions of major divisions of the spine (usually between the thoracic and lumbar vertebral junction and the lumbar and sacral vertebral junction). Transitional vertebrae take on anatomic characteristics of both divisions of the spine it occurs between. The most common type of transitional vertebrae reported by the OFA is in the lumbar-sacral area where the last lumbar vertebral body takes on anatomic characteristics of the sacrum. Transitional vertebrae are usually not associated with clinical signs and the dog can be used in a breeding program. The OFA recommends breeding the dog to a dog with a clear family history for transitional vertebrae."

      "Spondylosis is another incidental radiographic finding where smooth new bone production is visualized between vertebral bodies at the intervertebral disc spaces. The new bone production can vary in extent from formation of small bone spurs to complete bridging of adjacent vertebral bodes. Spondylosis may occur secondary to spinal instability but often it is of unknown cause and clinically insignificant. A familial basis for its development has been reported. Like transitional vertebrae, dogs with spondylosis can be used in breeding programs. It is recommended however, that they not be bred to others with the same condition."

      Many, many dogs are living normal lives and exhibiting no clinical signs despite showing radiographic evidence of spondylosis and transitional vertebrae. The OFA does not see either of these conditions as reasons to remove a dog from a breeding program.

      My suggestion for the researchers of the Isle Royale wolves would be to take a "wait and see" approach. Clearly, the wolves are well able to bring down bull moose to feed on. They are not hampered in their long treks of 30 miles per day. Most never live long enough for the spondylosis to be able to progress (if it does) to the point of severely hampering mobility and survival. Wolves of advanced age (8 to 10 years) have been found on the island.

      The predator - prey balance on the Isle Royale is tenuous at best. Introducing wolves is a risky prospect. Wolves are well known for killing strange wolves so the introduced wolves may not survive their "introduction". The moose are being severely impacted by the winter tick infestation (maybe something should be done about that?). Bringing in more wolves could result in a devastation of the moose population by (1) "potentially" fitter wolves (without spondylosis and transitional vertebrae *if* these conditions are truly impacting on the fitness of Isle Royale wolf) and (2) potentially increased wolf population (if the introduced wolves are able to establish themselves). Natural selection will over time select for the fittest wolves and it may be that the spinal abnormalities found in the skeletal remains of the Isle Royale wolves have not reached the threshold at which point fittness is impacted, and in fact due to natural selection may never reach that point of threshold.

      So my position remains one of "wait and see".

      If the wolves of Isle Royale go extinct or reach dangerously low levels then outside wolves can easily be introduced at any point if desired.

      But until there is solid evidence that the wolves can no longer fend for themselves and/or are manifesting signs of distress, then they should, in my opinion, be left alone.

      With dogs, breeders can xray spines and make appropriate breeding decisions. But how could such an approach be used with the wolves of Isle Royale? Even if they could be sedated and xrayed, how would one go about controlling mate selection? Use AI's sure, but once they are released they would just go mate with a related wolf that likely also has spondylosis and transitional vertebrae.

      At this point in time the spinal abnormalities are not producing evidence that the wolves fittness is affected. Bodies found by researchers, as reported on the The Wolves and Moose of Isle Royale site died due to one being killed by an alpha male, another from falling through the ice and presumably drowning, and another from injuries sustained during a moose attack. There is some suggestion that the wolf injured by the moose may have not been nimble enough to avoid being kicked. Reading the account of the bull moose attack where the wolves were hanging by their teeth from the rump of the moose and sustaining kicks, it's pretty clear that the most pristine spine would not enable a wolf to avoid getting kicked while hanging on to the rear end of a powerful kicking moose!

      These wolves have survived on the Isle Royale for 51 years now; if inbreeding was going to lead to their demise, it would have done so by now. Both the moose and the wolves have been highly inbred since the 1900's and 1950's respectively, yet according to John Vucetich, Michigan Tech scientist and now the lead scientist in the 51-year-old study of moose and wolves on the island: “Wolves right now are surprisingly holding their own. And moose are fairly steady as well, maybe down some’’. Vucetich also noted "it’s not clear if the deformities are hurting the overall wolf population or just individual animals. So far, wolf numbers have not crashed from the problem" (from Isle Royale wolves suffering from inbreeding: Scientists uncertain whether population needs “genetic rescue’

      The research team studying the Isle Royale wolves is looking for public opinion on whether they should intervene or not. Why not add you own opinion?

      Do Isle Royale Wolves Need Genetic Rescuing?

      What do you think?


      Morgan, J.P. & Cleta, S. B. (2000). Exercises in veterinary radiology: spinal disease. Wiley-Blackwell.

      Burke, R.L., Feeney, D.A., & Ackerman, N. (2003). Small animal radiology and ultrasonography: a diagnostic atlas and text (3rd edition). Elsevier Health Sciences.


      Unknown said...

      The problem with either side of this is that you and Terrierman are both ignoring the most salient part: SELECTION.

      Mother Nature can only use what is there, so if she has no normal spines to use, she will do her best with what is available. If these wolves die out, it is due to an unhealthy, closed population to begin with, not "inbreeding" per se.

      Terrierman seems to assume that Breeders aimlessly inbreed simply to produce puppies and that there is little to no selection used. This is where he is wrong. In the case of Isle Royale, it is artificial selection that would have prevented OR will turnaround the effects of the defective genes.

      Terrierman, like many of his ilk, believe that constant out-crossing is the answer to all that ails domestic animals. This "method" of basically random breeding will only assist in spreading defective recessives further throughout the population. What then? Out-cross with another SPECIES?

      It may in the end simply be a case of an island that was never capable of supporting a large predator and a large prey animal for any length of time. It is not analogous with humans using inbreeding with domestic animals. Is he suggesting that we go back to the hunter/gather type society? Because without humans making educated breeding choices for animals, we would have no domestic animals.

      A dog breed is already inbred. Does he believe that he can out-cross his terriers to any dog that will chase rodents and still have a workable terrier? Of course not.

      I believe that Terrierman and others like him believe that inbreeding is just fine as long as it is done for their ends. These are the type of people that still believe that PETA will leave them alone because they have "working" dogs. I am here to tell them that PETA is more concerned with those cute mice and fluffy sheep and pretty birds than they are with those folks "working" dogs.

      But hey, the AKC is a much easier target, right?

      Blog for Show Dogs said...

      There may be clear spines and wolves free of transitional vertebrae that natural selection will favour if the wolves actually are or become debilitated by these abnormalities. Only 58% of skeletal remains are showing these abnormalities, which leaves a possible 42% possibly clear wolves for nature to favour over time. It may well be the island can't support the population but it has defyed expectations for some time now, I for one would like to see the results to the end, if there is an end. I really appreciate what you said with regard to continuous outcrossing not being the answer and getting backed into corners with no where to go. So many proponents of genetic diversity and low COI's just don't get that. There is a place for the knowledgeable application of every breeding method (inbreeding/ linebreeding/ outcrossing), in the right hands of course.

      Anonymous said...

      I know this is an old post, but I have a two year old with a transitional vertebra that has caused enough problems to retire her from agility (she's 2!!!) And at least once a month she is in pain from the transitional vertebra. It's making her more prone to soft-tissue injuries along her spine.

      A quiet, housepet may not be affected by this. But working dogs, active dogs, and competitive dogs can be. Is it worth it? No. I have a highly intelligent, highly driven dog whose body is failing her just as she's getting started.