Hybridization between Wolves and Dogs

Abstract

Crossbreeding between wolves and dogs in the wild has been sometimes reported, but always poorly documented in scientific literature. However, documenting frequency of hybridisation and introgression is important for conservation of wild living wolf populations and for the management of free ranging dogs. Here we report the results of molecular genetic analyses of 31 wolf samples collected in Latvia from 1997 to 1999, including six pups originated from a litter found in northern Latvia in March 1999, and six wolves showing morphological traits that suggested hybrid origin. Nucleotide sequencing of the hypervariable part of the mtDNA control-region and genotyping of 16 microsatellite loci suggested that both pups and the morphologically anomalous wolves might originate from crossbreeding with dogs. Causes of wolf-dog crossbreeding, as well as possible management effort to avoid further hybridisation in the wild, are discussed.

Introduction

All species in the genus Canis are closely related and can interbreed and produce fertile offspring. Interbreeding may present conservation problems if it threatens the genetic integrity of endangered wild canids. There are numerous reports of wild or domestic canids hybridizing with rare or endangered species. For example, the Ethiopian wolf ( C. simensis ), a unique wolf-like species and the world's most endangered canid, is threatened by hybridization with domestic dogs ( C. familiaris ). Red wolves ( C. rufus ) may hybridize with coyotes in the wild, and gray wolves ( C. lupus ) and coyotes ( C. latrans ) interbreed in the Great Lakes region of North America. Gray wolves and dogs are the most closely related large canids. During the last 100,000 years domestic dogs may have originated from and interbred with wolves several times.

Dog breeders and many North American cultures occasionally crossed their dogs with wolves to improve vigor (Schwartz 1997). More than 10,000 wolf-dog hybrids may exist in the United States (García-Moreno et al. 1996). Dog-wolf interbreeding may have an ancient history: archaeological remains from Agate Basin Site in Wyoming suggest that wolf-dog hybridization may have occurred in North America 10,000 years ago (Schwartz 1997). Hybridization between gray wolves and dogs is thought to be most frequent near human settlements where wolves are found in low densities and where feral and domestic dogs are common (Boitani 1983; Bibikov 1988; Blanco et al. 1992). Boitani (1984) hypothesized that after a severe bottleneck before 1980, Italian wolves were numerically augmented through hybridization with dogs. Recently, Butler (1994) suggested that European wolf populations were in fact mainly hybrids between dogs and wolves. Although such inferences are based on anecdotal evidence, the genetic integrity of wild wolf populations is a real concern among conservationists (Blanco et al. 1992; Boitani 1993). Few genetic tests, however, have been done to determine the magnitude of hybridization in the wild.

Recent studies provide evidence that natural hybridization between gray wolves and domestic dogs is a much rarer event than is implied by the level of concern. The most extensive genetic studies have utilized maternally inherited mitochondrial DNA (mtDNA) markers that can identify ...