Widespread occurrence of a domestic dog mitochondrial DNA haplotype in southeastern US coyotes

Sequence analysis of the mitochondrial DNA control region from 112 southeastern US coyotes (Canis latrans) revealed 12 individuals with a haplotype closely related to those in domestic dogs. Phylogenetic analyses grouped this new haplotype in the dog/grey wolf (Canis familiaris/Canis lupus) clade with 98% bootstrap support. These results demonstrate that a male coyote hybridized with a female dog, and female hybrid offspring successfully integrated into the coyote population. The widespread distribution of this haplotype from Florida to West Virginia suggests that the hybridization event occurred long ago before the southeastern USA was colonized by coyotes. However, it could have occurred in the southeastern USA before the main front of coyotes arrived in the area between male coyotes released for sport and a local domestic dog. The introgression of domestic dog genes into the southeastern coyote population does not appear to have substantially affected the coyote's genetic, morphological, or behavioural integrity. However, our results suggest that, contrary to previous reports, hybridization can occur between domestic and wild canids, even when the latter is relatively abundant. Therefore, hybridization may be a greater threat to the persistence of wild canid populations than previously thought.

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title: The problems with hybrids: setting conservation guidelines
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title: Analysis of Hybrid Zones
abstract: Hybrid zones are, roughly speaking, narrow regions in which genetically distinct populations meet, mate, and produce hybrids. They are often only a few hundred meters wide and yet may be several hundred kilometers long. They are found in a wide variety of organisms: Tables 1 and 2 list about 150 reasonably clear examples, in which there is a spatial transition between two hybridizing forms. Such a widespread and striking phenomenon requires explanation; more importantly, it offers us several ways of understanding the nature and origin of species. First, hybrid zones pose interesting questions for the taxonomist, for they contrast two views of the species: as a set of populations delimited by genetic barriers to gene exchange; and as a set of populations maintained in a particular stable equilibrium by selection. Second, the wide range of genotypes found in a hybrid zone can be used to analyze the genetic differences and selective forces that separate the taxa involved. This may allow some inferences about the way these differences evolved and, by extrapolation, about the way fully isolated species diverge from each other. Finally, models of parapatric speciation, and of Wright's "shifting balance," involve the formation, move­ ment, and modification of hybrid zones. Hybrid zones must be understood before the plausibility of these models can be judged. After clarifying our terminology, we will summarize the relevant theory and then see how this can be used to make inferences from field data. A notable increase in the number of detailed genetic studies of hybrid zones occurred over

title: Extinction by hybridization and introgression
abstract: ▪ Abstract Nonindigenous species can bring about a form of extinction of native flora and fauna by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially problematic for rare species coming into contact with more abundant ones. Increased use of molecular techniques focuses attention on the extent of this underappreciated problem that is not always apparent from morphological observations alone. Some degree of gene flow is a normal, evolutionarily constructive process, and all constellations of genes and genotypes cannot be preserved. However, hybridization with or without introgression may, nevertheless, threaten a rare species' existence.

title: Genetic divergence among populations of the Hawaiian duck, laysan duck, and mallard
abstract: Allozymic variation at 20 gene loci was estimated for populations of the Laysan Duck (Anas laysanensis) and the Hawaiian Duck (A. wyvilliana) from the Hawaiian archipelago, as well as for Mallard populations (A. platyrhynchos) from Hawaii and North America. The Laysan Duck and Hawaiian Duck are endemic, have experienced severe bottlenecks, and are listed as endangered species. Alternative alleles are fixed at six loci for Mallards versus Hawaiian anatids (Hawaiian and Laysan ducks). In contrast, every allelic variant found in the Laysan Duck was present in the Hawaiian Duck (but not vice versa), suggesting the former is an offshoot of the latter. The genetic distance (Nei's D) between Laysan and Hawaiian ducks is less than 0.01, while that between both Hawaiian and Laysan ducks and Mallards is greater than 0.45. The allozymic evidence also suggests that there has been extensive hy- bridization between Mallards and Hawaiian Ducks on Oahu, with the near disappearance of Hawaiian Duck alleles. However, there is only slight evidence of Mallard genic introgression into the Hawaiian Duck population on Kauai. Finally, the allozymic data suggest that the Hawaiian Duck is a distinct species from the Mallard, but that little genetic divergence has occurred between Hawaiian and Laysan ducks. Received 25 July 1991, accepted 8 March 1992.

title: Hybridization in the Catalina Island Mountain Mahogany (Cercocarpus traskiae): RAPD Evidence
abstract: The Catalina Island mountain mahogany is one of 10 species of shrubs and small trees (Lis 1992) comprising the genus Cercocarpus H. B. K (Rosaceae). Species in the genus are widely distributed throughout western North America and are delimited primarily on the basis of leaf characteristics (Mortenson 1973; Lis 1992). The Catalina Island mountain mahogany (C. traskiae Eastwood) is one of the most distinctive species in the genus due to its thick, coriaceous leaves and woolly pubescence on the leaf undersurface. The species is extremely rare, restricted to Wild Boar Gully on the southwest side of Santa Catalina Island in the Channel Islands off the coast of California . When the population was first discovered in 1897, it consisted of over 40 individuals (Thorne 1967). Due to overgrazing by introduced mammalian herbivores (Coblentz 1980; Hobbs 1980), however, the population has been greatly reduced (Rieseberg et al. 1989). Cercocarpus traskiae is listed as endangered by the state of California and thus is afforded protection by California law (Smith & Berg 1988). Inexplicably, the species is not listed as endangered or threatened by the U.S. Fish and Wildlife Service, although it is under consideration for listing. In the late 1970s a detailed inventory of the Wild Boar Gully population was undertaken, and a total of eight Cercocarpus trees were discovered and tagged (Martin 1984). In addition, two of the trees (A, B; Fig. 1) were fenced to protect them from herbivores, and in 1985 the Catalina Conservancy constructed a larger fence around an area that included both trees, as well as about an acre of good habitat. The fencing effort was extremely successful, and by 1988 approximately 70 seedlings were observed within the fenced area (Rieseberg et al. 1989). Unfortunately, several of the adult plants resembled the island mountain mahogany, Cercocarpus betuloides Torrey & A. Gray var. blancbeae (C. Schneider) Little, in key morphological features such as leaf pubescence and leaf thickness or were immediate for these characters (descriptions of both species are given by R. Lis in Hickman [1993]). Cercocarpus betuloides var. blancbeae is only slightly more widespread than C traskiae, occurring on all of the Channel Islands except San Clemente. But the species is much more abundant than C traskiae on Santa Catalina and is known to occur in adjacent canyons, so the possibility of hybridization between the two species could not be dismissed. Furthermore, it is suspected that some of the seedlings might be of hybrid origin (T. Martin, personal communication). In an attempt to clarify the identity of morphologically ambiguous individuals, Rieseberg et al. (1989) undertook a study of allozymic variation and leaf anatomy of all the adult mahogany trees discovered in Wild Boar Gully. Of the eight adult trees in the Gully, three were anatomically intermediate between C. traskiae and C betuloides var. blancbeae, suggestive of hybridization. Analysis of 17 isozyme loci in C traskiae, as well as a nearby population of C betuloides var. blancbeae , revealed one diagnostic isozyme polymorphism differentiating the two species. Based on this single isozyme polymorphism, five of the eight trees were diagnosed as C traskiae, one as C betuloides var. blancbeae, and two as hybrids. However, isozyme analyses of the 28 seedlings large enough to survive the loss of a single leaf revealed all to be "pure" C traskiae. The results from this study were not entirely satisfactory, however, because the classification of individuals as parental versus hybrid was based on a single locus. The use of a single diagnostic locus can ensure the correct identification of first-generation hybrids, but F2or later-generation hybrid or backcross progeny could easily be misdiagnosed as belonging to one of the parental classes. Thus, it was not surprising that two of the plants lacking a hybrid enzyme genotype were anatomically Paper submitted April 1994; revised manuscript accepted July 15, 1994.

title: Molecular Genetics of Pre‐1940 Red Wolves
abstract: Conservation of the endangered red wolf (Canis rufus) has become a controversial issue because its genetic and morphological composition has been altered by hybridization with coyotes (C. latrans) and possibly gray wolves (C. lupus) making its evolutionary origins difficult to ascertain. The evolutionary hypothesis based on morphological data is that the red wolf had an Early Pleistocene origin and was the predecessor of both modern coyotes and gray wolves. After 1940 red wolves hybridized with coyotes as the species vanished from the wild. In contrast to this ancient origin-recent introgression hypothesis, molecular data are more consistent with an origin through hybridization between gray wolves and coyotes. Interspecific hybridization may have occurred repeatedly over time prior to European settlement in the southcentral United States or may have been induced recently by anthropogenic changes. We review recent molecular evidence and present new results from the analysis of mitochondrial and nuclear DNA markers in pre-1940 populations of red wolves. Our results are inconsistent with an ancient origin of the red wolf and support the hybridization model. We discuss possible hybridization scenarios and reasons for the red wolf reintroduction program to be concerned with the effects of genetic introgression from coyotes.

title: Molecular genetics of the most endangered canid: the Ethiopian wolf Canis simensis
abstract: The world's most endangered canid is the Ethiopian wolf Canis simensis, which is found in six isolated areas of the Ethiopian highlands with a total population of no more than 500 individuals. Ethiopian wolf populations are declining due to habitat loss and extermination by humans. Moreover, in at least one population, Ethiopian wolves are sympatric with domestic dogs, which may hybridize with them, compete for food, and act as disease vectors. Using molecular techniques, we address four questions concerning Ethiopian wolves that have conservation implications. First, we determine the relationships of Ethiopian wolves to other wolf‐like canids by phylogenetic analysis of 2001 base pairs of mitochondrial DNA (mtDNA) sequence. Our results suggest that the Ethiopian wolf is a distinct species more closely related to gray wolves and coyotes than to any African canid. The mtDNA sequence similarity with gray wolves implies that the Ethiopian wolf may hybridize with domestic dogs, a recent derivative of the gray wolf. We examine this possibility through mtDNA restriction fragment analysis and analysis of nine microsatellite loci in populations of Ethiopian wolves. The results imply that hybridization has occurred between female Ethiopian wolves and male domestic dogs in one population. Finally, we assess levels of variability within and between two Ethiopian wolf populations. Although these closely situated populations are not differentiated, the level of variability in both is low, suggesting long‐term effective population sizes of less than a few hundred individuals. We recommend immediate captive breeding of Ethiopian wolves to protect their gene pool from dilution and further loss of genetic variability.

title: Patterns of differentiation and hybridization in North American wolflike canids, revealed by analysis of microsatellite loci.
abstract: Genetic divergence and gene flow among closely related populations are difficult to measure because mutation rates of most nuclear loci are so low that new mutations have not had sufficient time to appear and become fixed. Microsatellite loci are repeat arrays of simple sequences that have high mutation rates and are abundant in the eukaryotic genome. Large population samples can be screened for variation by using the polymerase chain reaction and polyacrylamide gel electrophoresis to separate alleles. We analyzed 10 microsatellite loci to quantify genetic differentiation and hybridization in three species of North American wolflike canids. We expected to find a pattern of genetic differentiation by distance to exist among wolflike canid populations, because of the finite dispersal distances of individuals. Moreover, we predicted that, because wolflike canids are highly mobile, hybrid zones may be more extensive and show substantial changes in allele frequency, relative to nonhybridizing populations. We demonstrate that wolves and coyotes do not show a pattern of genetic differentiation by distance. Genetic subdivision in coyotes, as measured by theta and Gst, is not significantly different from zero, reflecting persistent gene flow among newly established populations. However, gray wolves show significant subdivision that may be either due to drift in past Ice Age refugia populations or a result of other causes. Finally, in areas where gray wolves and coyotes hybridize, allele frequencies of gray wolves are affected, but those of coyotes are not. Past hybridization between the two species in the south-central United States may account for the origin of the red wolf.

title: Hybridization between Wolves and Dogs
abstract: Concern has been expressed that European populations of gray wolves (Canis lupus) have extensively hybridized with domestic dogs (C. familiaris). We reviewed and analyzed surveys of mitochondrial and biparentally inherited genetic markers in dogs and wild populations of wolf-like canids. Although dog-wolf hybrids have been observed in the wild, significant introgression of dog markers into wild wolf populations has not yet occurred. Our investigation suggests that hybridization may not be an important conservation concern even in small, endangered wolf populations near human settlements. The behavioral and physiological differences between domestic dogs and gray wolves may be sufficiently great such that mating is unlikely and hybrid offspring rarely survive to reproduce in the wild.

title: A study of dog-coyote hybrids and implications concerning hybridization in canis.
abstract: A female, mongrel, black and white, 25-pound terrier dog bred to a captive male Kansas coyote gave birth on 20 April 1954 to six F1 hybrid “coy-dogs” From 1956 through 1961 these produced four litters of F2 hybrids. Five of the F1 generation resembled melanistic, short-legged coyotes; the sixth was similarly colored but shaggy like the mother. The F2 generation was more varied, dog-like to somewhat coyote-like animals.

Behavior varied, but all of the animals were intermediate, with some coyote-like traits, including howling. They were aggressive among themselves and had a dominance hierarchy in males and probably in females, with males dominating females. They displayed no submissive behavior adequate to inhibit a dominant individual from attacking an inferior. No trace of male parental care (which is strong in coyotes and absent in dogs) was noted in the coy-dogs.

The generally small size of the F2 litters (mean 2.25, range 1 to 3) and their small number in relation to the possible number, suggests some decrease in fecundity but might also have resulted from crowding or other suboptimal conditions inducing prenatal mortality. There was a rather high incidence of dental anomaly among the hybrids.

Both sexes of the hybrids, as in the comparatively few comparable studies, displayed a late autumnal, annual mating season (in this case in December), differing from that of coyotes, which breed in late winter (mainly February). The literature of dog-coyote hybridism is summarized and the implications of the peculiar reproductive timing of hybrids are discussed with respect to the possibility of hybridization in the wild leading (a) to the establishment of hybridswarms of coy-dogs and intermediate individuals; (b) to the introgression of dog genes into coyote populations; and (c) to the probable source of the extremely large size and remarkably great variation of a population of wild, coyote-like animals recently established in New England.

It is concluded that the phase shift in the breeding season of F1 hybrids, requiring the young of animals presumably less fit than coyotes to be reared in midwinter and in the absence of male parental care should form an effective, if not absolute, block to the development of hybrid swarms and to the introgression of dog genes into the coyote gene pool. Application of discriminant functions analysis—here applied also to various hybrids—to a series of wild Kansas coyotes (which are as much exposed to dogs as any coyotes) shows that these specimens have none of the unusual variability characterizing the New England population. It is therefore concluded that the variability and large size of the New England canids result from the introgression of wolf genes, probably in Ontario, into coyote stock. Recent proof that these species can in fact hybridize is cited. Also, two captive-reared coyote-wolf hybrids, long ago reported but later widely over-looked, seem likely in fact to represent this cross if judged by discriminant functions analysis and by their small size.

title: DNA profiles of the eastern Canadian wolf and the red wolf provide evidence for a common evolutionary history independent of the gray wolf
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title: Early Domesticated Dogs of the Near East
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title: Mitochondrial DNA Variability in Italian and East European Wolves: Detecting the Consequences of Small Population Size and Hybridization
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title: Multiple and ancient origins of the domestic dog.
abstract: Mitochondrial DNA control region sequences were analyzed from 162 wolves at 27 localities worldwide and from 140 domestic dogs representing 67 breeds. Sequences from both dogs and wolves showed considerable diversity and supported the hypothesis that wolves were the ancestors of dogs. Most dog sequences belonged to a divergent monophyletic clade sharing no sequences with wolves. The sequence divergence within this clade suggested that dogs originated more than 100,000 years before the present. Associations of dog haplotypes with other wolf lineages indicated episodes of admixture between wolves and dogs. Repeated genetic exchange between dog and wolf populations may have been an important source of variation for artificial selection.

title: Hybridization and the phylogenetic relationship between polecats and domestic ferrets in Britain
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title: Wolf-dog genetics
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