Post by Admin on Nov 2, 2020 5:01:35 GMT
Later homogenization of dog ancestry in Europe
The extensive range of ancestry diversity among early European dogs is not preserved today, as modern European dogs are all symmetrically related to the ancient dogs in our dataset (Fig. 1C, fig. S13, and data file S1) (30). This suggests little to no contribution of most local Mesolithic and Neolithic populations to present-day diversity in Europe. Instead, we found that a single dog from a Neolithic megalithic context dated to 5 ka ago at the Frälsegården site in southwestern Sweden can be modeled as a single-source proxy for 90 to 100% of the ancestry of most modern European dogs, to the exclusion of all other ancient dogs (fig. S13 and data file S1). This implies that a population with ancestry similar to this individual, but not necessarily originating in Scandinavia, replaced other populations and erased the continent-wide genetic cline (Fig. 5B). This ancestry was in the middle of the cline (Fig. 1C), and so present-day European dogs can be modeled as having about-equal proportions of Karelian- and Levantine-related ancestries [54 and 46%, respectively, for German shepherd on the basis of the admixture graph (Fig. 1E)].
The Frälsegården dog is also favored as a partial ancestry source for a 4-ka-old Bronze Age dog from Italy, a 1.5-ka-old dog from Turkey and Byzantine and Medieval, but not earlier dogs in the Levant (data file S1), providing some constraints on the timing of this ancestry expansion. However, the circumstances that initiated or facilitated the homogenization of dog ancestry in Europe from a narrow subset of that present in the European Neolithic, including the phenomenal phenotypic diversity and genetic differentiation of modern breeds (12, 19, 20) (Fig. 1C), remain unknown.
More recently, this modern European ancestry has dispersed globally and today is a major component of most dog populations worldwide (Fig. 5A). Our ancestry models, however, reveal that some precolonial ancestry does survive in breeds such as the Mexican chihuahua (~4%) and Xoloitzcuintli (~3%) and the South African Rhodesian ridgeback (~4%) (data file S1).
Discussion
The diversification of at least five dog ancestry lineages by the onset of the Holocene was followed by a dynamic population history that in many ways tracked that of humans, likely reflecting how dogs migrated alongside human groups. However, in several instances, these histories do not align, suggesting that humans also dispersed without dogs, dogs moved between human groups, or that dogs were cultural and/or economic trade commodities.
Certain aspects of genetic relationships between dog populations, such as an east–west Eurasian differentiation, circumpolar connections, and possible basal lineages in the Near East, resemble features of human population history that were established before the earliest estimated dates of dog domestication. This superficial mirroring between the species may therefore instead point to recurrent population dynamics due to biogeographic or anthropological factors that remain to be understood. A key question is how dogs spread across Eurasia and the Americas by the Holocene, since no major human population movements have been identified after the initial out-of-Africa expansion that could have driven this global dispersal.
We find that the modern and ancient genomic data are consistent with a single origin for dogs, though a scenario involving multiple closely related wolf populations remains possible. However, in our view, the geographical origin of dogs remains unknown. Previously suggested points of origin based upon present-day patterns of genomic diversity (2, 8, 10) or affinities to modern wolf populations (12) are sensitive to the obscuring effects of more recent population dynamics and gene flow. Ultimately, integrating DNA from dogs and wolves even older than those analyzed here with archaeology, anthropology, ethology, and other disciplines is needed to determine where and in which environmental and cultural context the first dogs originated.
The extensive range of ancestry diversity among early European dogs is not preserved today, as modern European dogs are all symmetrically related to the ancient dogs in our dataset (Fig. 1C, fig. S13, and data file S1) (30). This suggests little to no contribution of most local Mesolithic and Neolithic populations to present-day diversity in Europe. Instead, we found that a single dog from a Neolithic megalithic context dated to 5 ka ago at the Frälsegården site in southwestern Sweden can be modeled as a single-source proxy for 90 to 100% of the ancestry of most modern European dogs, to the exclusion of all other ancient dogs (fig. S13 and data file S1). This implies that a population with ancestry similar to this individual, but not necessarily originating in Scandinavia, replaced other populations and erased the continent-wide genetic cline (Fig. 5B). This ancestry was in the middle of the cline (Fig. 1C), and so present-day European dogs can be modeled as having about-equal proportions of Karelian- and Levantine-related ancestries [54 and 46%, respectively, for German shepherd on the basis of the admixture graph (Fig. 1E)].
The Frälsegården dog is also favored as a partial ancestry source for a 4-ka-old Bronze Age dog from Italy, a 1.5-ka-old dog from Turkey and Byzantine and Medieval, but not earlier dogs in the Levant (data file S1), providing some constraints on the timing of this ancestry expansion. However, the circumstances that initiated or facilitated the homogenization of dog ancestry in Europe from a narrow subset of that present in the European Neolithic, including the phenomenal phenotypic diversity and genetic differentiation of modern breeds (12, 19, 20) (Fig. 1C), remain unknown.
More recently, this modern European ancestry has dispersed globally and today is a major component of most dog populations worldwide (Fig. 5A). Our ancestry models, however, reveal that some precolonial ancestry does survive in breeds such as the Mexican chihuahua (~4%) and Xoloitzcuintli (~3%) and the South African Rhodesian ridgeback (~4%) (data file S1).
Discussion
The diversification of at least five dog ancestry lineages by the onset of the Holocene was followed by a dynamic population history that in many ways tracked that of humans, likely reflecting how dogs migrated alongside human groups. However, in several instances, these histories do not align, suggesting that humans also dispersed without dogs, dogs moved between human groups, or that dogs were cultural and/or economic trade commodities.
Certain aspects of genetic relationships between dog populations, such as an east–west Eurasian differentiation, circumpolar connections, and possible basal lineages in the Near East, resemble features of human population history that were established before the earliest estimated dates of dog domestication. This superficial mirroring between the species may therefore instead point to recurrent population dynamics due to biogeographic or anthropological factors that remain to be understood. A key question is how dogs spread across Eurasia and the Americas by the Holocene, since no major human population movements have been identified after the initial out-of-Africa expansion that could have driven this global dispersal.
We find that the modern and ancient genomic data are consistent with a single origin for dogs, though a scenario involving multiple closely related wolf populations remains possible. However, in our view, the geographical origin of dogs remains unknown. Previously suggested points of origin based upon present-day patterns of genomic diversity (2, 8, 10) or affinities to modern wolf populations (12) are sensitive to the obscuring effects of more recent population dynamics and gene flow. Ultimately, integrating DNA from dogs and wolves even older than those analyzed here with archaeology, anthropology, ethology, and other disciplines is needed to determine where and in which environmental and cultural context the first dogs originated.