Academic journal article Genetics

Unequal Contribution of Sexes in the Origin of Dog Breeds

Academic journal article Genetics

Unequal Contribution of Sexes in the Origin of Dog Breeds

Article excerpt

ABSTRACT

Dogs ( Canis familiaris) were domesticated from the gray wolf ( Canis lupus) at least 14,000 years ago, and there is evidence of dogs with phenotypes similar to those in modern breeds 4000 years ago. However, recent genetic analyses have suggested that modern dog breeds have a much more recent origin, probably <200 years ago. To study the origin of contemporaneous breeds we combined the analysis of paternally inherited Y chromosome markers with maternally inherited mitochondrial DNA and biparentally inherited autosomal microsatellite markers in both domestic dogs and their wild ancestor, the gray wolf. Our results show a sex bias in the origin of breeds, with fewer males than females contributing genetically, which clearly differs from the breeding patterns in wild gray wolf populations where both sexes have similar contributions. Furthermore, a comparison of mitochondrial DNA and Y chromosome diversity in dog groups recognized by the World Canine Organization, as well as in groups defined by the breeds' genetic composition, shows that paternal lineages are more differentiated among groups than maternal lineages. This demonstrates a lower exchange of males than of females between breeds belonging to different groups, which illustrates how breed founders may have been chosen.

DOGS (Canis familiaris) were domesticated from gray wolves (Canis lupus) at least 14,000 years ago (ViLA et al. 1997; SABLIN and KHLOPACHEV 2002; SAVOLAINEN et al. 2002), well before the domestication of any other animal or plant species (GLUTTON-BROCK 1999). Genetic analyses suggest a limited number of domestication events with subsequent transcontinental spread (ViLA et al. 1997; LEONARD et al. 2002; SAVOLAINEN et al. 2002), and archaeological evidence confirms that domestic dogs existed across at least three continents by 10,000 years ago (SCHWARTZ 1997; GLUTTON-BROCK 1999; SABLIN and KHLOPACHEV 2002). This relatively fast spread of dogs across continents suggests that they may have played an important role in primitive human societies.

The roles fulfilled by modern dogs are many and varied, but likely different from those in Stone Age communities. The World Canine Organization (Fédération Cynologique Internationale, FCI) currently recognizes ^347 breeds of dogs, classified in 10 groups according to their function and, to a lesser degree, area of origin (for example, group 10 contains sighthounds; see Table 2 legend). Modern breeds differ widely in size, conformation, behavior, and physiology (HART 1995; COPPINGER and COPPINGER 2001; WAYNE and VILA 2001). The phenotypical differences among dog breeds exceed those among breeds of other domestic mammals and even between species in the entire family Canidae (WAYNE 1986a,b).

Ancient origins have been claimed for some dog breeds (CROWLEY and ADELMAN 1998). Archaeological evidence from ancient Egypt suggests that several types of morphologically differentiated dogs (similar to mastiffs and greyhounds) existed 4000 years ago, and Romans may have been the first people to develop dog breeds in Europe as early as the first century A.D. (GLUTTON-BROCK 1999). Dogs on paintings from the sixteenth century can be easily recognized today as spaniels, mastiffs, hounds, pointers, etc. However, this long history contrasts with the results of genetic studies, which suggest that most of the current breeds may represent a recent radiation from a common stock and that distinct breeds may have been formed from "less codified phenotypic varieties after the introduction of the breed concept and the creation of breed clubs in Europeinthe 180Os" (PARKER ^aZ. 2004, p. 1164). The genetic comparison of dog breeds using autosomal markers shows that breeds constitute well-defined entities, differentiated from each other (ZAjC and SAMPSON 1999; KOSKINEN 2003; DENISE et al 2004; PARKER et al 2004). On the other hand, mitochondria! DNA (mtDNA) comparisons fail to show clear differentiation between breeds (UKUMURA et al. …

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