September 25, 2020

Multilocus Detection of Wolf x Dog Hybridization in Italy, and Guidelines for Marker Selection

*Editor’s Note* – The following study should come as no surprise to those with knowledge and an honest approach to scientific wolf study. Hybridization between canine species is something that happens in nature, but is exceptionally enhanced by several events, one of which is, of course, human intervention and manipulation. Wolves with the least amount of hybridization were found in geographically isolated regions. Expanding populations of wolves increases the likelihood of hybridization and that is magnified when such expansions force wolves into human-settled landscapes and especially where dogs exist and are free ranging – the more dogs the greater the risk of hybridization.

This study confirms what many of us have been saying for several years; that forcing or introducing wolves into areas that are not geographically isolated (to protect the species), promotes hybridization, which in turns leads to the destruction of the wolf gene. 

Teddy Roosevelt wrote a great deal about his observances of different species of wild canines and determined that, at that time in history, wolf species were geographically isolated, and, as such, contributed to his and other’s ability to distinguish wolf species, i.e. big wolf and little wolf.

As a society with responsibility to care for our animal species, rational thought should lead us to conclude that we should be working hard to do what we can to keep wolves – those with the least amount of mixed genes – geographically isolated. The worst thing we can do is a continuation of forcing more and more wolves onto the landscape, thus heavily promoting hybridization and a destruction of the species. Or, we can do as some have suggested: simply acknowledging that all wild dogs are a species that should be protected regardless of its genetic composition. 

That makes absolutely no sense.

<<<Read Entire Study>>>

Hybridization and introgression can impact the evolution of natural populations. Several wild canid species hybridize in nature, sometimes originating new taxa. However, hybridization with free-ranging dogs is threatening the genetic integrity of grey wolf populations (Canis lupus), or even the survival of endangered species (e.g., the Ethiopian wolf C. simensis). Efficient molecular tools to assess hybridization rates are essential in wolf conservation strategies. We evaluated the power of biparental and uniparental markers (39 autosomal and 4 Y-linked microsatellites, a melanistic deletion at the b-defensin CBD103 gene, the hypervariable domain of the mtDNA control-region) to identify the multilocus admixture patterns in wolf x dog hybrids. We used empirical data from 2 hybrid groups with different histories: 30 presumptive natural hybrids from Italy and 73 Czechoslovakian wolfdogs of known hybrid origin, as well as simulated data. We assessed the efficiency of various marker combinations and reference samples in admixture analyses using 69 dogs of different breeds and 99 wolves from Italy, Balkans and Carpathian Mountains. Results confirmed the occurrence of hybrids in Italy, some of them showing anomalous phenotypic traits and exogenous mtDNA or Y-chromosome introgression. Hybridization was mostly attributable to village dogs and not strictly patrilineal. The melanistic b-defensin deletion was found only in Italian dogs and in putative hybrids. The 24 most divergent microsatellites (largest wolf-dog FST values) were equally or more informative than the entire panel of 39 loci. A smaller panel of 12 microsatellites increased risks to identify false admixed individuals. The frequency of F1 and F2 was lower than backcrosses or introgressed individuals, suggesting hybridization already occurred some
generations in the past, during early phases of wolf expansion from their historical core areas. Empirical and simulated data indicated the identification of the past generation backcrosses is always uncertain, and a larger number of ancestryinformative markers is needed.

The frequency of backcrosses or introgressed individuals (87.5%) between wolf and dog is far higher than the frequency of F1 and F2 hybrids (12.5%), suggesting that hybridization events already occurred in Italy some generations in the past. Probably this happened during the early phases of population re-expansion in Italy, when wolves moved from their historical core areas in the central-southern Apennines and colonized the northern Apennine mountains and lower hills [61]. Theoretical expectations [97] and empirical findings [29,43] indicate that the risk of hybridization is higher in the periphery of wolf distributions in human-dominated landscapes, where wolf populations are less dense, free-ranging dogs are more abundant and early dispersing wolves have more probabilities to meet and mate with dogs. Expanding wolf populations will inevitably spread further into anthropogenically altered areas, where settlement density, infrastructure and the presence of agricultural activities will likely increase traffic
casualties, illegal wolf killings. Consequently high pack turnover can contribute to further raise hybridization frequency. These findings suggest that: 1) expanding wolf populations may experience higher hybridization risks than stable populations; 2) the dynamics of hybridization and introgression will change through time, with a maximum expectancy of hybridization during the early phases of the colonization waves, followed by the subsequent spread of hybrids and the generation of backcrosses within wild populations. The spatial and temporal dynamics of hybridization and backcrossing should be conditioned by landscape features, anthropogenic factors, wolf and feral dog initial
population density and colonization rates. These variables could be modelled using landscape genetic tools to reconstruct maps of hybridization risks, thus providing important resources for the monitoring and management of wolf populations in Europe.