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 are 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 is usually from a wolf that had been wearing a radio collar.
Copyright © John A. Vucetich — All rights reserved
Wolf Skeletons
Malformities
Patterns
Consequences
Should anything be done?
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.
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.
33% of Isle Royale wolves have 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, which are highly inbred and suffer from 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 one or more 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 2008, we collected 7 skeletons. All of these had malformations. A normal wolf has not been observed since 1993.
The effects of genetic deterioration might be mitigated by gene flow. That is, by bringing unrelated wolves, from possibly Minnesota or Ontario, to Isle Royale. This possibility raises the question: Should such mitigation should 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.
Rolf Peterson discusses some of these issues in his 1995 book, Broken Balance (reprinted in 2008 by University of Michigan Press). Then the intention was to better understand the appropriateness of reintroduction should Isle Royale wolves go extinct. That discussion focused on (i) the aesthetic and scientific values of perpetuating a predator-prey system largely unaffected by humans, and (ii) how to balance mandates associated with Isle Royale’s designation as U. S. Federal Wilderness, which values minimizing human intervention but also values actively mitigating past anthropogenic effects. In 1995, Rolf Peterson took for granted the appropriateness of not intervening while wolves persisted in order to maximize the prospect of improved scientific understanding of population viability in small populations.
Assessing the appropriateness of bringing new wolves to Isle Royale now seems complicated by several new considerations. First, we now know genetic deterioration has, at least, compromised the anatomy of these wolves. Given current knowledge about population viability and the non-experimental circumstances characterizing Isle Royale, as much scientific insight might be gained by assessing the potential effects of genetic rescue as from continuing to observe the effects of population isolation.
Second, the potential benefits of gene flow to wolves may be unexpectedly detrimental to the viability of wolf-moose interactions on Isle Royale. That is, because ticks and other factors associated with climate warming have been increasingly impacting moose, a more vigorous wolf population could be importantly detrimental to moose. Third, genetic deterioration now seems to have been causing individual wolves to suffer – suffering that might be mitigated by intervention.
Any decision about intervening on Isle Royale seems to involve balancing the value of basic scientific knowledge, health of ecological collectives (i.e., population viability and ecosystem health), the welfare of individual animals, and what is taken to be a virtue for wilderness areas, non-intervention. In this way, the Isle Royale case is an example of a general and profound challenge for environmental ethics.
The consequences of these deformities have not been well studied in wild wolves (Canis lupus). However, the consequences are well understood among domestic dogs (Canis lupus familiaris).
Domestic dogs with LSTV tend to suffer from a condition called cauda equina syndrome (CES), which entails injury at the end of 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 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.
Ventral view of wolf # 3387 which exhibited lumbosacral transitional vertebrae with severe changes at sacrum with an anomalous disk space (top, left). The top right image shows normal sacral segments.
Cranial view of wolf #3529 that exhibited a unilateral intrasegmental transitional vertebra at C7 (above, left). One side of the vertebra resembles C6 with a transverse foramen (arrow). For comparison, the right photo shows the C7 of a normal wolf.
We recently documented how Isle Royale wolves suffer high rates of bone malformities, which are almost certainly caused by inbreeding. The kinds of malformities we observed can cause pain and partial paralysis, and can inhibit locomotion when they occur in domestic dogs. The text below details these observations. Much of this text is adapted from: Congenital bone deformities and the inbred wolves (Canis lupus) of Isle Royale by J Raikkonen, JA Vucetich, RO Peterson, MP Nelson, which is to be published in a 2009 issue of Biological Conservation.
This subordinate female from Middle Pack fell through the ice in January 2005. We found her skeleton on the beach near Siskiwit Bay Camp Ground the following spring.
