Surprisingly, inbred isle royale wolves dwindle because of fewer harmful genes

Genomic signatures of extensive inbreeding in Isle Royale wolves, a population on the threshold of extinction

American Association for the Advancement of Science

The tiny, isolated gray wolf population on Isle Royale has withered to near-extinction, but not because each animal carries a large number of harmful genes, according to a new genetic analysis. Instead, each one has been more likely to inherit the same harmful recessive alleles from both parents. This pattern enables expression of related genes as physical deformities, including the population's characteristically crooked spines. The findings contradict many previous studies, which suggest the crux of the genetic problem for historically small or sharply reduced populations is an increase in the quantity of harmful alleles. While the Isle Royale wolf population once consisted of 50 wolves, it has dwindled to just two - a father and daughter that are also half siblings. The collapse of the Isle Royale wolf population occurred despite a reported genetic "rescue" in 1997 by a single migrant from the mainland. To better characterize the genome-wide effects of intense inbreeding and isolation on this population, and their role in its decline, Jacqueline A. Robinson and colleagues analyzed mutations within the protein-coding regions of DNA from Isle Royale wolves, compared with genetic data from wolves in nearby mainland Minnesota. The former didn't have a greater number of deleterious genes than the Minnesota group, but the proportion of Isle Royale wolves with paired harmful recessive alleles in their genome was 38.4% higher. When the researchers compared Isle Royale genetic data with that from other wolf genomes from around the world, they found that individuals from historically large populations more frequently contained two different alleles at a gene location, while those from historically small populations more frequently contained short sequences of identical allele pairings, as with the Isle Royale wolves. These findings, supported by further simulations, contain broader implications for conservation efforts to manage fragmented populations at risk for decline due to inbreeding. Individuals brought in from historically small populations, rather than those from larger, more diverse gene pools, may actually prove more beneficial because they carry fewer potentially harmful alleles.