When I was 13 years old I had a deep interest in America’s national parks, so I have long been familiar with the ecology and conservation genetics work associated with Isle Royale. In particular, there has been a long-term study of the predator-prey dynamics on the island dating back decades. Before the recent resurgence of the wolf across the West, the Isle Royale pack was not an inconsequential proportion of the national headcount in the lower 48 states.
But these wolves were always on a knife’s edge. The island is small, and there were never more than a few dozen wolves. This is below the generally accepted minimum census size for a viable long-term population. And in fact, the Isle Royale wolves are newcomers, descending from a pair that arrived in the 1940s. Census size aside, this fact itself points to the likelihood that these wolves are going to be plagued by the downsides of inbreeding. Not only is there average population size rather small, but their genealogies coalesce back to a very small bottleneck, possibly an original mating pair.
Now the wolves of Isle Royale are back to where they began: with a single pair. And these two are not promising candidates for the perpetuation of the population. From Science:
A few years ago, eight to nine wolves roamed the island, but the population dwindled to three last year. The remaining two are the most closely related of the group. The inbreeding coefficient of their potential offspring—a measure that varies between zero for unrelated parents to approaching one after many generations of brother-sister mating—is 0.438. (By comparison, the inbreeding coefficient among some of the European Habsburgs was 0.25, according to a 2009 analysis.) Some captive and experimental animal populations approach this level of inbreeding, but such populations are prone to abnormalities—and extinction—and managers try to avoid it. Wolves themselves naturally avoid mating with such close kin, but the pair on Isle Royale have no other options….
The male is the father of the female. They are also half-siblings, as they share the same mother (so the male is the son of a female with whom he mated to produce the female who is his current mate). If mating with near relatives over generations could purge the genetic load of deleterious alleles in a mammalian population, these wolves would have done so. As it happens apparently the wolves of Isle Royale have suffered from typical ailments of inbreeding and reduced fertility for a while.