New Study Reveals Extent of Cross-Breeding between Domestic Dogs and Wolves

University of Lincoln researcher Malgorzata Pilot and colleagues have found small blocks of dog ancestry in the genomes of 62% Eurasian grey wolves. Published in the journal Evolutionary Applications, their work suggests that wolf-dog hybridization has been geographically widespread in Europe and Asia and has been occurring for centuries; the phenomenon is seen less frequently in wolf populations of North America.

Pilot et al showed that around 60% of Eurasian grey wolf genomes carried small blocks of the DNA of domestic dogs, suggesting that wolves cross-bred with dogs in past generations. Image credit: J. C.

Dr. Pilot and co-authors examined DNA data from grey wolves (Canis lupus) to determine how much their gene pool was diluted with the DNA of domestic dogs (Canis lupus familiaris), and how widespread the process of hybridization is.

Despite the evidence of hybridization among Eurasian grey wolves, the wolf populations have remained genetically distinct from dogs, suggesting that such cross-breeding does not diminish distinctiveness of the wolf gene pool if it occurs at low levels.

The results could have important conservation implications for the grey wolf, which is a keystone species — meaning it is vital to the natural balance of the habitat it occupies. The legal status of hybrids is still uncertain and unregulated.

“The fact that wild wolves can cross-breed with dogs is well-documented, but little was previously known about how widespread this phenomenon has been and how it has affected the genetic composition of wild wolf populations,” Dr. Pilot said.

“We found that while hybridization has not compromised the genetic distinctiveness of wolf populations, a large number of wild wolves in Eurasia carry a small proportion of gene variants derived from dogs, leading to the ambiguity of how we define genetically ‘pure’ wolves.”

Results of ancestry block analysis in LAMP for two chromosomes, shown as an example; dog ancestry is marked in red and wolf ancestry in yellow; each row represents one individual, with dogs followed by wolves and admixed canids; a part of the graph is enlarged to show individual hybrids and back-crosses. Image credit: Pilot et al, doi: 10.1111/eva.12595.

“Our research highlighted that some individual wolves which had been identified as ‘pure’ wolves according to their physical characteristics were actually shown to be of mixed ancestry,” she said.

“On the other hand, two Italian wolves with an unusual, black coat color did not show any genetic signatures of hybridization, except for carrying a dog-derived variant of a gene linked to dark coloration.”

“This suggests that the definition of genetically ‘pure’ wolves can be ambiguous and identifying admixed individuals can be difficult, implying that management strategies based on removal of suspected hybrids from wolf populations may be inefficient.”

“Instead, our study has highlighted a need to reduce the factors which can cause hybridization, such as abundance of free-ranging dogs, small wolf population sizes, and unregulated hunting.”

Studying a specific type of genetic variation in the DNA sequences of wolves and domestic dogs — called Single Nucleotide Polymorphisms (SNPs) — the scientists identified the transfer of dog gene variants into wolf genomes.

A single DNA sequence is formed from a chain of four nucleotide bases and if some individuals in a population do not carry the same nucleotide at a specific position in the sequence, the variation is classified as an SNP.

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Ma?gorzata Pilot et al. Widespread, long-term admixture between grey wolves and domestic dogs across Eurasia and its implications for the conservation status of hybrids. Evolutionary Applications, published online March 8, 2018; doi: 10.1111/eva.12595