No crossbreeding in the Scandinavian wolf population

From a purely biological viewpoint, crossbreeding between domesticated dogs and wolves pose a threat to the genetic integrity of wildlife in many areas across the world where these two species live side-by-side. In Scandinavia, the wolf population seems to not follow this general pattern. Recent research led by Uppsala University in Sweden has revealed the absence of wolf-dog crossbreeding in this population. The results from this project have also confirmed the origin of the contemporary Scandinavian wolf population.

Please also read: Wolf hybrids, friend or foe?

Although commonly mistaken as hybridisation, the mixing of wolf and domesticated dog genes results from a case of natural crossbreeding. Hybrids are the offspring of two different species and are often sterile. However, natural crossbreeding occurs between two animals from different breeds or varieties of the same species. This is what occurs between the wolves and domesticated dogs as the domestic dog (Canis lupus familiaris) is technically a sub-species of the wolf (Canis lupus). This results in any offspring between the two groups being fertile and being able to spread their genes further.

Genetic integrity intact

Crossbreeding has increased in the last centuries due to greater human influence in the natural world. This has occurred particularly in relation to human-induced instances of organism transport and habitat modification. As a result, domesticated animals tend to now outnumber their wild counterparts, making crossbreeding a real threat to wildlife. When humans accidentally release domestic animals , they can damage the genetic integrity of wild populations if interbreeding occurs. This poses a threat to natural genetic diversity and can lead to the extinction of certain species, if the crossbreed variant turns out to be fitter in the wild environment.

Notwithstanding these fears, scientists working on this research found that the Scandinavian wolf population shared less than 1% of mixed ancestry with dogs. Likewise, the same was also true for dogs. In terms of crossbreeding between the wolf and dog, these figures are too low to signal such an occurrence.

While instances of genes switching between dogs and wolves have been observed before, there are reasons as to why it has not occurred in the Scandinavian region. The presence of feral dogs in Scandinavia is limited. As a result, there are few possibilities for this crossbreeding to occur in the first place. However, even when it does take place, monitoring and management strategies are in place to remove crossbreeds before they are able to breed with wild wolf populations again. Examples of this include the culling of crossbred offspring from female wolves and male dogs in 1999, in Norway, and in 2017, in Sweden. Consequently, these quick actions have made it difficult for crossbreeding to fully take hold in the Scandinavian wolf population.

please-sign-petition-against-wolf-killing-in-italy.jpg - © European Wilderness Society CC BY-NC-ND 4.0
© European Wilderness Society CC BY-NC-ND 4.0

Origin of the Scandinavian wolves

Wolves were common in Scandinavia until the 1960s when they became extinct. However, scientists discovered a new population in the 1980s. Immigrant wolves then came from the Finnish–Russian Karelian population to supplement the number of wolves on the Scandinavian peninsula. Subsequently, this helped reduce the potential for inbreeding. The population then spread out from there towards the west, in the direction of Norway, and towards the north, in the direction of northern Sweden. In addition, migration flows have occurred in both directions. Scandinavian born wolves have also been found in Finland and Russia.

We’ve probably never had a specific Scandinavian population. Throughout the ages, wolves have likely moved back and forth between the Scandinavian peninsula and regions to the east.

Hans Ellegren
Professor of Evolutionary Biology at Uppsala University

Gene analysis conducted in this research confirmed these previously contested assertions. Before this, there were fears that there was crossbreeding with domestic dogs due to their initial isolation from the eastern populations. Thanks to this research, more is now known about the Scandinavian wolf population, regarding their origin and crossbreeding status.

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One thought on “No crossbreeding in the Scandinavian wolf population

  • A nice article highlighting an important study. Just two minor comments: It is indicated in the article that in terms of wolf-dog hybridization Scandinavia is somewhat different from other regions, which is only partially true. In many countries of western and central Europe, for instance, we have very few cases of hybridization as well, and the reasons seem to be the same, namely few feral dogs, an intense scientific monitoring, and consequent removal of hybrids. In fact, the common guess that hybridization between wolves and dogs is a universal problem is most likely not correct. It may become one for sure in some regions, but a sound monitoring and management will allow for the long-term persistence of a distinct wolf gene pool even within human-dominated landscapes.
    Secondly, you mention that hybridization is the wrong term for admixture between wolves and domestic dogs, as they are not different species. This is not correct, however, as hybridization is not strictly defined as crossbreeding between different species. Crossbreeding between different genetic lineages, subspecies or populations is commonly named “intraspecific hybridization” in the scientific literature and is used as complement to “interspecific hybridization”. Thus, it is correct to refer to “wolf-dog hybrids”. In contrast, the term used in the article, “natural crossbreeding”, makes no sense here at all. Crossbreeding between species is as natural as crossbreeding between populations within a species, although in most cases it is more rare. Modern genomics shows that most animal and plant species must have hybridized at some point with other species, as most genomes include DNA of other closely related species. Hybridization between species commonly contributes to the formation of new species and may simply be regarded as another effective mechanism of the most “natural” process on earth: Biological evolution. If wolf-dog hybridization is a form of “natural hybridization”, as stated here, is rather a philosophical issue and depends if you consider products of human culture, such as domestic dogs, as “natural”. This is why science uses the term “anthropogenic hybridization” in such cases where hybridization occurs through human impact (by creating domestic forms hybridizing with their natural ancestors or by translocating wild species that will hybridize with other wild species).
    Carsten Nowak, Senckenberg

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