Barking up the wrong tree: modern northern European dogs fail to explain their origin

Population Dynamics in Italian Canids between the Late Pleistocene and Bronze Age

Dog domestication is still largely unresolved due to time-gaps in the sampling of regions. Ancient Italian canids are particularly understudied, currently represented by only a few specimens. In the present study, we sampled 27 canid remains from Northern Italy dated between the Late Pleistocene and Bronze Age to assess their genetic variability, and thus add context to dog domestication dynamics. They were targeted at four DNA fragments of the hypervariable region 1 of mitochondrial DNA. A total of 11 samples had good DNA preservation and were used for phylogenetic analyses. The dog samples were assigned to dog haplogroups A, C and D, and a Late Pleistocene wolf was set into wolf haplogroup 2. We present our data in the landscape of ancient and modern dog genetic variability, with a particular focus on the ancient Italian samples published thus far. Our results suggest there is high genetic variability within ancient Italian canids, where close relationships were evident between both a ~24,700 years old Italian canid, and Iberian and Bulgarian ancient dogs. These findings emphasize that disentangling dog domestication dynamics benefits from the analysis of specimens from Southern European regions.

Origins and genetic legacy of prehistoric dogs

Dogs were the first domestic animal, but little is known about their population history and to what extent it was linked to humans. We sequenced 27 ancient dog genomes and found that all dogs share a common ancestry distinct from present-day wolves, with limited gene flow from wolves since domestication but substantial dog-to-wolf gene flow. By 11,000 years ago, at least five major ancestry lineages had diversified, demonstrating a deep genetic history of dogs during the Paleolithic. Coanalysis with human genomes reveals aspects of dog population history that mirror humans, including Levant-related ancestry in Africa and early agricultural Europe. Other aspects differ, including the impacts of steppe pastoralist expansions in West and East Eurasia and a near-complete turnover of Neolithic European dog ancestry.

Analysis of new retrogenes provides insight into dog adaptive evolution

The origin and subsequent evolution of new genes have been considered as an important source of genetic and phenotypic diversity in organisms. Dog breeds show great phenotypic diversity for morphological, physiological, and behavioral traits. However, the contributions of newly originated retrogenes, which provide important genetic bases for dog species differentiation and adaptive traits, are largely unknown. Here, we analyzed the dog genome to identify new RNA-based duplications and comprehensively investigated their origin, evolution, functions in adaptive traits, and gene movement processes. First, we totally identified 3,025 retrocopies including 476 intact retrogenes, 2,518 retropseudogenes, and 31 chimerical retrogenes. Second, selective pressure along with ESTs expression analysis showed that most of the intact retrogenes were significantly under stronger purifying selection and subjected to more functional constraints when compared to retropseudogenes. Furthermore, a large number of retrocopies and chimerical retrogenes that occurred approximately 22 million years ago implied a burst of retrotransposition in the dog genome after the divergence time between dog and its closely related species red fox. Interestingly, GO and pathway analyses showed that new retrogenes had expanded in glutathione biosynthetic/metabolic process which likely provided important genetic basis for dogs' adaptation to scavenge human waste dumps. Finally, consistent with the results in human and mouse, a significant excess of functional retrogenes movement on and off the X chromosome in the dog confirmed a general pattern of gene movement process in mammals which was likely driven by natural selection or sexual antagonism. Together, these results increase our understanding that new retrogenes can reshape the dog genome and provide further exploration of the molecular mechanisms underlying the dogs' adaptive evolution.

A cryptic mitochondrial DNA link between North European and West African dogs

Domestic dogs have an ancient origin and a long history in Africa. Nevertheless, the timing and sources of their introduction into Africa remain enigmatic. Herein, we analyse variation in mitochondrial DNA (mtDNA) D-loop sequences from 345 Nigerian and 37 Kenyan village dogs plus 1530 published sequences of dogs from other parts of Africa, Europe and West Asia. All Kenyan dogs can be assigned to one of three haplogroups (matrilines; clades): A, B, and C, while Nigerian dogs can be assigned to one of four haplogroups A, B, C, and D. None of the African dogs exhibits a matrilineal contribution from the African wolf (Canis lupus lupaster). The genetic signal of a recent demographic expansion is detected in Nigerian dogs from West Africa. The analyses of mitochondrial genomes reveal a maternal genetic link between modern West African and North European dogs indicated by sub-haplogroup D1 (but not the entire haplogroup D) coalescing around 12,000 years ago. Incorporating molecular anthropological evidence, we propose that sub-haplogroup D1 in West African dogs could be traced back to the late-glacial dispersals, potentially associated with human hunter-gatherer migration from southwestern Europe.

Taming the Past: Ancient DNA and the Study of Animal Domestication

During the last decade, ancient DNA research has been revolutionized by the availability of increasingly powerful DNA sequencing and ancillary genomics technologies, giving rise to the new field of paleogenomics. In this review, we show how our understanding of the genetic basis of animal domestication and the origins and dispersal of livestock and companion animals during the Upper Paleolithic and Neolithic periods is being rapidly transformed through new scientific knowledge generated with paleogenomic methods. These techniques have been particularly informative in revealing high-resolution patterns of artificial and natural selection and evidence for significant admixture between early domestic animal populations and their wild congeners.

Genetic structure in village dogs reveals a Central Asian domestication origin

Dogs were the first domesticated species, originating at least 15,000 y ago from Eurasian gray wolves. Dogs today consist primarily of two specialized groups--a diverse set of nearly 400 pure breeds and a far more populous group of free-ranging animals adapted to a human commensal lifestyle (village dogs). Village dogs are more genetically diverse and geographically widespread than purebred dogs making them vital for unraveling dog population history. Using a semicustom 185,805-marker genotyping array, we conducted a large-scale survey of autosomal, mitochondrial, and Y chromosome diversity in 4,676 purebred dogs from 161 breeds and 549 village dogs from 38 countries. Geographic structure shows both isolation and gene flow have shaped genetic diversity in village dog populations. Some populations (notably those in the Neotropics and the South Pacific) are almost completely derived from European stock, whereas others are clearly admixed between indigenous and European dogs. Importantly, many populations--including those of Vietnam, India, and Egypt-show minimal evidence of European admixture. These populations exhibit a clear gradient of short--range linkage disequilibrium consistent with a Central Asian domestication origin.

Establishing the validity of domestication genes using DNA from ancient chickens

Modern domestic plants and animals are subject to human-driven selection for desired phenotypic traits and behavior. Large-scale genetic studies of modern domestic populations and their wild relatives have revealed not only the genetic mechanisms underlying specific phenotypic traits, but also allowed for the identification of candidate domestication genes. Our understanding of the importance of these genes during the initial stages of the domestication process traditionally rests on the assumption that robust inferences about the past can be made on the basis of modern genetic datasets. A growing body of evidence from ancient DNA studies, however, has revealed that ancient and even historic populations often bear little resemblance to their modern counterparts. Here, we test the temporal context of selection on specific genetic loci known to differentiate modern domestic chickens from their extant wild ancestors. We extracted DNA from 80 ancient chickens excavated from 12 European archaeological sites, dated from ∼ 280 B.C. to the 18th century A.D. We targeted three unlinked genetic loci: the mitochondrial control region, a gene associated with yellow skin color (β-carotene dioxygenase 2), and a putative domestication gene thought to be linked to photoperiod and reproduction (thyroid-stimulating hormone receptor, TSHR). Our results reveal significant variability in both nuclear genes, suggesting that the commonality of yellow skin in Western breeds and the near fixation of TSHR in all modern chickens took place only in the past 500 y. In addition, mitochondrial variation has increased as a result of recent admixture with exotic breeds. We conclude by emphasizing the perils of inferring the past from modern genetic data alone.

Phylogenetic distinctiveness of Middle Eastern and Southeast Asian village dog Y chromosomes illuminates dog origins

Modern genetic samples are commonly used to trace dog origins, which entails untested assumptions that village dogs reflect indigenous ancestry or that breed origins can be reliably traced to particular regions. We used high-resolution Y chromosome markers (SNP and STR) and mitochondrial DNA to analyze 495 village dogs/dingoes from the Middle East and Southeast Asia, along with 138 dogs from >35 modern breeds to 1) assess genetic divergence between Middle Eastern and Southeast Asian village dogs and their phylogenetic affinities to Australian dingoes and gray wolves (Canis lupus) and 2) compare the genetic affinities of modern breeds to regional indigenous village dog populations. The Y chromosome markers indicated that village dogs in the two regions corresponded to reciprocally monophyletic clades, reflecting several to many thousand years divergence, predating the Neolithic ages, and indicating long-indigenous roots to those regions. As expected, breeds of the Middle East and East Asia clustered within the respective regional village dog clade. Australian dingoes also clustered in the Southeast Asian clade. However, the European and American breeds clustered almost entirely within the Southeast Asian clade, even sharing many haplotypes, suggesting a substantial and recent influence of East Asian dogs in the creation of European breeds. Comparison to 818 published breed dog Y STR haplotypes confirmed this conclusion and indicated that some African breeds reflect another distinct patrilineal origin. The lower-resolution mtDNA marker consistently supported Y-chromosome results. Both marker types confirmed previous findings of higher genetic diversity in dogs from Southeast Asia than the Middle East. Our findings demonstrate the importance of village dogs as windows into the past and provide a reference against which ancient DNA can be used to further elucidate origins and spread of the domestic dog.

Adaptation and niche construction in human prehistory: a case study from the southern Scandinavian Late Glacial

The niche construction model postulates that human bio-social evolution is composed of three inheritance domains, genetic, cultural and ecological, linked by feedback selection. This paper argues that many kinds of archaeological data can serve as proxies for human niche construction processes, and presents a method for investigating specific niche construction hypotheses. To illustrate this method, the repeated emergence of specialized reindeer (Rangifer tarandus) hunting/herding economies during the Late Palaeolithic (ca 14.7-11.5 kyr BP) in southern Scandinavia is analysed from a niche construction/triple-inheritance perspective. This economic relationship resulted in the eventual domestication of Rangifer. The hypothesis of whether domestication was achieved as early as the Late Palaeolithic, and whether this required the use of domesticated dogs (Canis familiaris) as hunting, herding or transport aids, is tested via a comparative analysis using material culture-based phylogenies and ecological datasets in relation to demographic/genetic proxies. Only weak evidence for sustained niche construction behaviours by prehistoric hunter-gatherer in southern Scandinavia is found, but this study nonetheless provides interesting insights into the likely processes of dog and reindeer domestication, and into processes of adaptation in Late Glacial foragers.

Regional occurrence, high frequency but low diversity of mitochondrial DNA haplogroup d1 suggests a recent dog-wolf hybridization in Scandinavia

The domestic dog mitochondrial DNA (mtDNA)-gene pool consists of a homogenous mix of haplogroups shared among all populations worldwide, indicating that the dog originated at a single time and place. However, one small haplogroup, subclade d1, found among North Scandinavian/Finnish spitz breeds at frequencies above 30%, has a clearly separate origin. We studied the genetic and geographical diversity for this phylogenetic group to investigate where and when it originated and whether through independent domestication of wolf or dog-wolf crossbreeding. We analysed 582 bp of the mtDNA control region for 514 dogs of breeds earlier shown to harbour d1 and possibly related northern spitz breeds. Subclade d1 occurred almost exclusively among Swedish/Finnish Sami reindeer-herding spitzes and some Swedish/Norwegian hunting spitzes, at a frequency of mostly 60–100%. Genetic diversity was low, with only four haplotypes: a central, most frequent, one surrounded by two haplotypes differing by an indel and one differing by a substitution. The substitution was found in a single lineage, as a heteroplasmic mix with the central haplotype. The data indicate that subclade d1 originated in northern Scandinavia, at most 480–3000 years ago and through dog-wolf crossbreeding rather than a separate domestication event. The high frequency of d1 suggests that the dog-wolf hybrid phenotype had a selective advantage.

Man's best friend becomes biology's best in show: genome analyses in the domestic dog

In the last five years, canine genetics has gone from map construction to complex disease deconstruction. The availability of a draft canine genome sequence, dense marker chips, and an understanding of the genome architecture has changed the types of studies canine geneticists can undertake. There is now a clear recognition that the dog system offers the opportunity to understand the genetics of both simple and complex traits, including those associated with morphology, disease susceptibility, and behavior. In this review, we summarize recent findings regarding canine domestication and review new information on the organization of the canine genome. We discuss studies aimed at finding genes controlling morphological phenotypes and provide examples of the way such paradigms may be applied to studies of behavior. We also discuss the many ways in which the dog has illuminated our understanding of human disease and conclude with a discussion on where the field is likely headed in the next five years.

Mitochondrial sequence variation in ancient horses from the Carpathian Basin and possible modern relatives

Movements of human populations leave their traces in the genetic makeup of the areas affected; the same applies to the horses that move with their owners This study is concerned with the mitochondrial control region genotypes of 31 archaeological horse remains, excavated from pre-conquest Avar and post-conquest Hungarian burial sites in the Carpathian Basin dating from the sixth to the tenth century. To investigate relationships to other ancient and recent breeds, modern Hucul and Akhal Teke samples were also collected, and mtDNA control region (CR) sequences from 76 breeds representing 921 individual specimens were combined with our sequence data. Phylogenetic relationships among horse mtDNA CR haplotypes were estimated using both genetic distance and the non-dichotomous network method. Both methods indicated a separation between horses of the Avars and the Hungarians. Our results show that the ethnic changes induced by the Hungarian Conquest were accompanied by a corresponding change in the stables of the Carpathian Basin.

mtDNA data indicate a single origin for dogs south of Yangtze River, less than 16,300 years ago, from numerous wolves

There is no generally accepted picture of where, when, and how the domestic dog originated. Previous studies of mitochondrial DNA (mtDNA) have failed to establish the time and precise place of origin because of lack of phylogenetic resolution in the so far studied control region (CR), and inadequate sampling. We therefore analyzed entire mitochondrial genomes for 169 dogs to obtain maximal phylogenetic resolution and the CR for 1,543 dogs across the Old World for a comprehensive picture of geographical diversity. Hereby, a detailed picture of the origins of the dog can for the first time be suggested. We obtained evidence that the dog has a single origin in time and space and an estimation of the time of origin, number of founders, and approximate region, which also gives potential clues about the human culture involved. The analyses showed that dogs universally share a common homogenous gene pool containing 10 major haplogroups. However, the full range of genetic diversity, all 10 haplogroups, was found only in southeastern Asia south of Yangtze River, and diversity decreased following a gradient across Eurasia, through seven haplogroups in Central China and five in North China and Southwest (SW)Asia, down to only four haplogroups in Europe. The mean sequence distance to ancestral haplotypes indicates an origin 5,400–16,300 years ago (ya) from at least 51 female wolf founders. These results indicate that the domestic dog originated in southern China less than 16,300 ya, from several hundred wolves. The place and time coincide approximately with the origin of rice agriculture, suggesting that the dogs may have originated among sedentary hunter-gatherers or early farmers, and the numerous founders indicate that wolf taming was an important culture trait.

Using classical population genetics tools with heterochroneous data: time matters!

BACKGROUND

New polymorphism datasets from heterochroneous data have arisen thanks to recent advances in experimental and microbial molecular evolution, and the sequencing of ancient DNA (aDNA). However, classical tools for population genetics analyses do not take into account heterochrony between subsets, despite potential bias on neutrality and population structure tests. Here, we characterize the extent of such possible biases using serial coalescent simulations.

METHODOLOGY/PRINCIPAL FINDINGS

We first use a coalescent framework to generate datasets assuming no or different levels of heterochrony and contrast most classical population genetic statistics. We show that even weak levels of heterochrony ( approximately 10% of the average depth of a standard population tree) affect the distribution of polymorphism substantially, leading to overestimate the level of polymorphism theta, to star like trees, with an excess of rare mutations and a deficit of linkage disequilibrium, which are the hallmark of e.g. population expansion (possibly after a drastic bottleneck). Substantial departures of the tests are detected in the opposite direction for more heterochroneous and equilibrated datasets, with balanced trees mimicking in particular population contraction, balancing selection, and population differentiation. We therefore introduce simple corrections to classical estimators of polymorphism and of the genetic distance between populations, in order to remove heterochrony-driven bias. Finally, we show that these effects do occur on real aDNA datasets, taking advantage of the currently available sequence data for Cave Bears (Ursus spelaeus), for which large mtDNA haplotypes have been reported over a substantial time period (22-130 thousand years ago (KYA)).

CONCLUSIONS/SIGNIFICANCE

Considering serial sampling changed the conclusion of several tests, indicating that neglecting heterochrony could provide significant support for false past history of populations and inappropriate conservation decisions. We therefore argue for systematically considering heterochroneous models when analyzing heterochroneous samples covering a large time scale.