To find a wolf skull is rare. To collect other parts of a wolf skeleton is especially rare. Wolf carcasses are small and their bones quickly scattered by foxes and ravens. Of the 250 or so wolves that have ever lived on Isle Royale, we have recovered partial or complete skeletons of just 36. We are lucky to find just one in a year. When we do collect a skeleton, it’s usually from a wolf that had been wearing a radio collar.
More about wolf skeletons...
More about the Isle Royale malformities...
Patterns of malformation...
The consequences of malformed vertrebrae...
Some ethical considerations...
Some time ago, we noticed that many of these wolf skeletons had asymmetrical vertebrae. To better understand these skeletal remains, we collaborated with Jannikke Raikkonen from the Swedish Museum of Natural History, an expert in mammalian anatomy. Her observations revealed an array of anomalies.
33% of Isle Royale wolves have the malformity known as LSTV.
By contrast, only 1% of wolves carry the malformity in populations that are not inbred, like those of modern-day Finland and Scandinavia before those wolves were extirpated by humans.
Even among modern-day Scandinavian wolves, who suffer inbreeding depression, just 10% have the LSTV malformation.
LSTV malformities are also more common among domestic dogs that are particularly inbred.
The probability that an Isle Royale wolf will be born with malformed vertebrae has increased dramatically over the past 50 years (dotted line). That increase corresponds with the continual genetic deterioration that Isle Royale wolves experience.
In this graph, each dot indicates the year of birth for a wolf (read off the horizontal axis) and the whether the wolf had a malformation (0=normal, and 1=malformed). The dotted curve estimates the probability that a wolf would have the malformation, given its year of birth.
Between 1995 and 2009, we collected 9 skeletons. All had malformations. A normal wolf has not been observed since 1993.
In the 1980s, there was concern that Isle Royale wolves might go extinct. Discussion followed about whether to reintroduce wolves should they ever go extinct from Isle Royale (see Broken Balance by Rolf Peterson). That discussion focused on (i) the aesthetic and scientific values of perpetuating a predator-prey system that is largely unaffected by humans, and (ii) how to balance the sometimes conflicting legal mandates associated with Isle Royale’s designation as U. S. Federal Wilderness. Those values include minimizing human intervention, but also intervening to mitigate past human effects.
That discussion also took for granted the appropriateness of not intervening while wolves persisted. Being able to study an extinction event, should it come to be, was thought to be more important for scientists looking to prevent other extinctions by better understanding them.
Today, judging the appropriateness of genetic rescue seems complicated by new considerations that involve balancing at least four sets of values:
- Basic scientific knowledge: Trying genetically rescue Isle Royale wolves might teach much about the possibility of genetic rescues for other endangered populations?
- Healthy ecosystems: Ticks and climate warming increasingly impact moose (for more info, click here). Would a more vigorous, genetically-rescued wolf population be serious trouble for moose? Is Isle Royale healthier when it has healthy populations of predator and prey? Would genetic rescue preserve or upset the balance between predator and prey?
- The welfare of individual animals: If wolves suffer from bone malformities, and if we might be able to reduce the future occurrence of such suffering, shouldn’t we try?
- Wilderness values: Isn’t non-intervention the most virtuous action? Do we have to meddle with everything in nature?
Although these deformities are not well studied in wild wolves (Canis lupus), the consequences domestic dogs (Canis lupus familiaris) are well understood. Domestic dogs with LSTV malformities tend to suffer from cauda equina syndrome (CES), which involves injury to the spinal cord and associated nerve roots. The consequences of CES are variable and include partial paralysis; deficits in placing reactions when walking; deficits in voluntary movement of the tail; loss of muscle tone causing weakness of the hind limbs and flaccidity of the tail, low back pain and incontinence.
Several Isle Royale individuals also exhibited asymmetries that would weaken the sacroiliac joint, and may accelerate degeneration of the disc and result in disc protrusions. Dogs exhibiting disk protrusion also tend to suffer low back pain and lameness. Asymmetries like those observed in Isle Royale wolves can also be associated with irregularities in gait and detrimental development of the hip joints.
On the left, the bones labeled S1, S2, S3 are a normal sacrum. These are the vertebrae that connect to your pelvis (hip bone). The bone labeled L7 is the 7th lumbar vertebra. It is the bone just above (for people) or just in front (for wolves) of the sacrum.
On the right, a malformed sacrum (S1, S2, S3) and the misshapen pelvis to which they connect. A more technical description: ventral view of wolf # 3387 which exhibited lumbosacral transitional vertebrae with severe changes at sacrum with an anomalous disk space.
The vertebra on the left is almost perfectly symmetrical. Draw a line down the middle, and you’ll see it’s left and right sides are the same. This is the normal condition.
The vertebra on the right is malformed and grossly asymmetrical.
The vertebra on the right has other serious problems, adequately described only in technical terms: The cranial view vertebra at C7 for Isle Royale wolf #3529 that exhibited a unilateral intrasegmental transitional (right). One side of the vertebra resembles C6 with a transverse foramen (arrow).
We recently discovered how Isle Royale wolves have been suffering from malformed vertebrae (backbone). The malformities are almost certainly caused by genetic deterioration.
These malformities, when they occur in domestic dogs, can cause pain, partial paralysis, and inhibited locomotion.
In January 2009, we discovered a wolf that likely died from being kicked by a moose. Despite being young, it had a severely arthritic back. The arthritis may have resulted from the malformities that also plagued his back. It’s easy to think this wolf’s inability to dodge the moose’s fatal kick is related to his malformed vertebrae.
It may be possible to reduce the future occurrence of these malformities by genetically rescuing Isle Royale wolves. A genetic rescue would involve bringing unrelated wolves to Isle Royale and allowing their genes to mix with the current population.
This possibility raises the question: Should a genetic rescue be attempted?. Because wolves often kill non-territorial wolves, such mitigation could be technically challenging. However, the appropriateness of an attempt also depends on important, unresolved ethical issues...
This subordinate female from Middle Pack fell through the ice in January 2005. We found her skeleton on the beach near Siskiwit Bay Campground the following spring.
Much of the text here was adapted from:
Congenital bone deformities and the inbred wolves (Canis lupus) of Isle Royale by J Raikkonen, JA Vucetich, RO Peterson, MP Nelson, published in a 2009 issue of Biological Conservation. doi:10.1016/j.biocon.2009.01.014
THE BASICS
All the technical details...
26% of the wolves had extra vertebrae. 58% had a malformation of one kind or another in the vertebral column. Some of these malformations were asymmetrical vertebrae. Others go by technical descriptions such as incomplete ossification of the cranial border of the first cervical vertebrae thoracolumbar transitional vertebrae, intrasegmental transitional vertebrae, and lumbosacral transitional vertebrae (LSTV).
An LSTV is a single vertebrae that possesses anatomical properties of both lumbral vertebrae and sacral vertebrae. LSTV are interesting because they are well-studied in dogs and wolves.
NORMAL
MALFORMED
NORMAL
MALFORMED
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This case of malformed wolves on Isle Royale is just one instance of many like it. How we balance these issues says much about what we think our place in nature should be.
The consequences of genetic deterioration in Isle Royale wolves