Mitochondrial DNA Variability of the Gray Wolf: Genetic Consequences of Population Decline and Habitat Fragmentation

The gray wolf is a large, highly mobile predator whose original geographic range included most of the Northern Hemisphere. High rates of genetic exchange probably characterized even distantly-separated populations in the past, but recent population declines and habitat fragmentation have isolated previously contiguous populations, especially in the Old World. We examine mitochondrial DNA (mtDNA) variability among twenty-six populations of wolves from throughout their geographic range. We find eighteen mtDNA genotypes in gray wolves, seven of these are derived from hybridization with coyotes, four are confined to the New World, six are confined to the Old World and one is shared by both areas. Genetic differentiation among wolf populations is significant but small in magnitude. In the Old World, most localities have a single unique genotype, whereas in the New World several genotypes occur at most localities and three of the five genotypes are nearly ubiquitous. The pattern of genetic differentiation in the gray wolf contrasts with that of another large, highly vagile canid, the coyote, in which genetic differentiation among populations is not significant even among widely separated localities. We suggest that the difference between these two species reflects the rapid, recent increase in coyote numbers and expansion of their geographic range, and the coincident decline in gray wolf populations. Apparent genetic differences among extant wolf populations may be a recent phenomenon reflecting population declines and habitat fragmentation rather than a long history of genetic isolation.     

Hybridization between Wolves and Dogs

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.     

Molecular Genetics of Pre-1940 Red Wolves

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.     

Dynamics of Hybridization and Introgression in Red Wolves and Coyotes

Abstract:  Hybridization and introgression are significant causes of endangerment in many taxa and are considered the greatest biological threats to the reintroduced population of red wolves ( Canis rufus ) in North Carolina (U.S.A.). Little is known, however, about these processes in red wolves and coyotes ( C. latrans ). We used individual-based simulations to examine the process of hybridization and introgression between these species. Under the range of circumstances we considered, red wolves in colonizing and established populations were quickly extirpated, persisted near the carrying capacity, or had intermediate outcomes. Sensitivity analyses suggested that the probabilities of quasi extinction and persistence of red wolves near the carrying capacity were most affected by the strength of two reproductive barriers: red wolf challenges and assortative mating between red wolves and coyotes. Because model parameters for these barriers may be difficult to estimate, we also sought to identify other predictors of red wolf population fate. The proportion of pure red wolves in the population was a strong predictor of the future probabilities of red wolf quasi extinction and persistence. Finally, we examined whether sterilization can be effective in minimizing introgression while allowing the reintroduced red wolf population to grow. Our results suggest sterilization can be an effective short-term strategy to reduce the likelihood of extirpation in colonizing populations of red wolves. Whether red wolf numbers are increased by sterilization depends on the level of sterilization effort and the acting reproductive barriers. Our results provide an outline of the conditions likely required for successful reestablishment and long-term maintenance of populations of wild red wolves in the presence of coyotes. Our modeling approach may prove generally useful in providing insight into situations involving complex species interactions when data are few.     

Genetic Variation of Naturally Colonizing Wolves in the Central Rocky Mountains

Recovery of gray wolf ( Canis lupus ) populations in North America depends on minimizing human-caused mortality and enhancing migration from stable source populations to suitable habitat unoccupied by wolves. We used a combination of field observation and DNA microsatellite genotyping to examine natural wolf colonization of Glacier National Park, Montana, and surrounding lands. We found high genetic variation in the colonizing population, showing that these packs were founded by multiple, unrelated wolves from Canada. High dispersal rates, long dispersal distances, and lack of a founding population bottleneck indicate that wolves in the United States and Canada should be viewed and managed as a single population. Restoration in the United States by artificial transplants from Alberta to Yellowstone National Park and central Idaho began in 1995. The transplanted wolves will likely aid demographic recovery, but permanently retaining the high genetic variation of wolves in the United States will require assuring gene flow throughout the central Rocky Mountains.     

Conservation Genetics of the Endangered Isle Royale Gray Wolf

Abstract. The small group of wolves on Isle Royale has been studied for over three decades as a model of the relationship between large carnivores and their prey. During the last ten years the population declined from 50 individuals to as few as 12 individuals. The causes of this decline may be food shortages, disease, or reduced genetic variability. We address the issues of genetic variability and relationships of Isle Royale wolves using allozyme electrophoresis, mtDNA restriction-site analysis, and multilocus hypervariable minisatellite DNA analysis (genetic fingerprinting). Our results indicate that approximately 50% of the allozyme heterozygosity has been lost in the island population, a decline similar to that expected if no immigration had occurred from the mainland. The genetic fingerprinting data indicate that the seven sampled Isle Royale wolves are as similar as captive populations of siblings. Surprisingly, the Isle Royale wolves have an mDNA genotype that is very rare on the mainland, being found in only one of 144 mainland wolves ThFF suggests that the remaining Isle Royale wolves areprobably derived from a single female founder     

Effects of Social Structure and Prey Dynamics on Extinction Risk in Gray Wolves

Extinction models based on diffusion theory generally fail to incorporate two important aspects of population biology—social structure and prey dynamics. We include these aspects in an individual-based extinction model for small, isolated populations of the gray wolf (Canis lupus). Our model predicts mean times to extinction significantly longer than those predicted by more general (diffusion) models. According to our model, an isolated population of 50 wolves has a 95% chance of surviving just 9 years and only a 30% chance of surviving beyond 100 years. Reflecting the influence of social structure, a wolf population initially comprising 50 individuals is expected to persist only a few years longer, on average (71 years), than is a population initially comprising just a single reproductive pair (62 years). In contrast, substantially greater average prey abundance leads to dramatically longer expected persistence times. Autocorrelated prey dynamics result in a more complex distribution of extinction times than predicted by many extinction models. We contend that demographic stochasticity may pose the greatest threat to small, isolated wolf populations, although environmental stochasticity and genetic effects may compound this threat. Our work highlights the importance of considering social structure and resource dynamics in the development of population viability analyses.     

Genetic Introgression of Endemic Taxa by Non-natives: A Case Study with Leon Springs Pupfish and Sheepshead Minnow

Genetic studies of a pupfish (Cyprinodon bovinus) endemic to a small, spring-fed system in west Texas illustrate the potential for small introductions of non-native species to cause large-scale genetic changes through hybridization and genetic introgression. We performed a genetic survey (allozymes and RFLP analysis of mtDNA) of four samples of C. bovinus representing all wild populations of the species and a captive population maintained since 1976 at Dexter, New Mexico. The results indicate genetic introgression of the entire wild population by sheepshead minnow (C. variegatus), a coastal species with a history of introductions in west Texas. Frequencies of foreign genetic elements averaged across four diagnostic allozyme loci and mtDNA varied from 6.1 to 15.1%. The captive population appears free of foreign genetic material. Comparisons with past studies of C. bovinus indicate the present situation is largely due to a recent introduction of C. variegatus, not to an introduction in the mid-1970s; however, residual effects from the earlier introduction cannot be completely discounted. Genetic analysis indicates that the source of introduced C. variegatus in Diamond Y Draw is the nearest known population, an introduced stock in Lake Balmorhea approximately 90 km away. The results demonstrate the value of maintaining imperiled species in captivity. Captive C. bovinus provide an opportunity to restore the genetic integrity of wild populations.     

The Genetic Diversity of Native, Stocked, and Hybrid Populations of Brook Trout in the Southern Appalachians

Using mitochondrial DNA (mtDNA) restriction analysis and starch-gel electrophoresis of the CK-A2 locus product, we examined genetic variation in 311 brook trout (Salvelinus fontinalis) from 11 native, 5 hatchery-derived, and 8 hybrid populations in the southern Appalachian Mountains. Native southern Appalachian fish were genetically distinct from hatchery-derived fish. Southern and hatchery-derived fish were reliably distinguished based on three mtDNA restriction sites. Native southern haplotypes differed from hatchery-derived haplotypes by an average of 0.84%. Northern hatchery-derived haplotypes varied little in mtDNA compared to native southern haplotypes. Introgression of mtDNA haplotypes and the CK-A2 locus varied among populations, and introgression of allozyme and mtDNA markers was positively correlated. Continued introductions of nonnative strains of brook trout in the southern Appalachians could simplify the genetic structure of native brook trout populations and eliminate unique genotypes.     

Genetic Structure and Migration in Native and Reintroduced Rocky Mountain Wolf Populations

Gray wolf (Canis lupus) recovery in the Rocky Mountains of the U.S. is proceeding by both natural recolonization and managed reintroduction. We used DNA microsatellite analysis of wolves transplanted from Canada to two reintroduction sites in the U.S. to study population structure in native and reintroduced wolf populations. Gene flow due to migration between regions in Canada is substantial, and all three recovery populations in the U.S. had high genetic variation. The reintroduced founders were moderately genetically divergent from the naturally colonizing U.S. population. These findings corroborate that the reintroduction more than meets generally accepted genetic guidelines. Maintaining this variation, however, will depend on ample reproduction in the first few generations. In the long term genetic variation will best be retained if migration occurs among the recolonizing and the two transplanted populations. Evidence from field observation and genetic studies shows extensive dispersal by wolves, and we conclude that exchange among these groups due to natural dispersal is likely if public tolerance and legal protection are adequate outside lands designated for wolf recovery.     

Paying for Tolerance: Rural Citizens' Attitudes toward Wolf Depredation and Compensation

Abstract:   As wolf ( Canis lupus ) populations recover in Wisconsin (U.S.A.), their depredations on livestock, pets, and hunting dogs have increased. We used a mail-back survey to assess the tolerance of 535 rural citizens of wolves and their preferences regarding the management of "problem" wolves. Specifically, we tested whether people who had lost domestic animals to wolves or other predators were less tolerant of wolves than neighboring residents who had not and whether compensation payments improved tolerance of wolves. We assessed tolerance via proxy measures related to an individual's preferred wolf population size for Wisconsin and the likelihood she or he would shoot a wolf. We also measured individuals' approval of lethal control and other wolf-management tactics under five conflict scenarios. Multivariate analysis revealed that the strongest predictor of tolerance was social group. Bear ( Ursus americanus ) hunters were concerned about losing valuable hounds to wolves and were more likely to approve of lethal control and reducing the wolf population than were livestock producers, who were more concerned than general residents. To a lesser degree, education level, experience of loss, and gender were also significant. Livestock producers and bear hunters who had been compensated for their losses to wolves were not more tolerant than their counterparts who alleged a loss but received no compensation. Yet all respondents approved of compensation payments as a management strategy. Our results indicate that deep-rooted social identity and occupation are more powerful predictors of tolerance of wolves than individual encounters with these large carnivores.     

The Status and Conservation of the Wolf in Gujarat and Rajasthan, India

Abstract: Populations of wolves were estimated for the states of Gujarat and Rajasthan, India, based on interviews and surveys. The wolf range is continuous. The total number of wolves in Gujarat is between 190 and 270 and in Rajasthan is between 253 and 350. Recommendations for a wolf conservation strategy include: (1) encouraging public support and education, (2) enforcing legal protection, (3) paying compensation for wolf-killed livestock, (4) conducting surveys of wolf populations and research on the dynamics of select populations, (5) protecting breeding habitats, and (6) eradicating feral dogs from wolf conservation areas. It is not too late to save the wolf if such a conservation strategy is implemented immediately.     

Distribution of male and female mtDNA lineages in populations of blue mussels,Mytilus trossulus and M. galloprovincialis,along the Pacific coast of North America

Geographic variation in mitochondrial large subunit (16S) ribosomal RNA haplotypes was examined for blue mussels, Mytilus trossulus Gould, 1850 and M. galloprovincialis Lamarck, 1819, sampled from ten sites along the Pacific coast of the USA in January of 1993. Using polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assays we determined haplotype frequencies for both the male and female mussel mitochondrial DNA (mtDNA) lineages. Populations from Morro Bay south to San Diego, California, contained only M. galloprovincialis male and female haplotypes, while those from Arcata Bay, California, north to Port Orford, Oregon, were fixed for M. trossulus haplotypes. Populations from Monterey Bay to Bodega Bay, California, contained a mixture of M. trossulus and M. galloprovincialis haplotypes. Overall only 2 of 97 heteroplasmic individuals had a mixed M. trossulus/M. galloprovincialis mitochondrial genotype indicating that hybridization is uncommon in the populations sampled. Further, there was no evidence of extensive introgression between these mussel taxa at the level of mtDNA. This is in contrast to previously published results which suggested the significant introgression of M. trossulus haplotypes into southern populations containing primarily M. galloprovincialis nuclear genotypes. We feel the discrepancy lies in the ability of our assays to detect haplotypes corresponding to both the male and female mtDNA lineages. Potential explanations for the lack of mtDNA introgression include, low levels of backcrossing between hybrids and parental taxa, epistatic interaction between nuclear and mitochondrial genes and the breakdown of a sex-specific inheritance pattern for mtDNA in hybrids.     

A study of the genetic relationships within and among wolf packs using DNA fingerprinting and mitochondrial DNA

Summary DNA fingerprinting and mitochondrial DNA analyses have not been used in combination to study relatedness in natural populations. We present an approach that involves defining the mean fingerprint similarities among individuals thought to be unrelated because they have different mtDNA genotypes. Two classes of related individuals are identified by their distance in standard errors above this mean value. The number of standard errors is determined by analysis of the association between fingerprint similarity and relatedness in a population with a known genealogy. We apply this approach to gray wolf packs from Minnesota, Alaska, and the Northwest Territories. Our results show that: (1) wolf packs consist primarily of individuals that are closely related genetically, but some packs contain unrelated, non-reproducing individuals; (2) dispersal among packs within the same area is common; and (3) short-range dispersal appears more common for female than male wolves. The first two of these genetically-based observations are consistent with behavioral data on pack structure and dispersal in wolves, while the apparent sex bias in dispersal was not expected.USA Offprint requests to: N. Lehman at the present address     

Desert pastoralists’ negative and positive effects on rare wildlife in the Gobi

In arid regions of the developing world, pastoralists and livestock commonly inhabit protected areas, resulting in human–wildlife conflict. Conflict is inextricably linked to the ecological processes shaping relationships between pastoralists and native herbivores and carnivores. To elucidate relationships underpinning human–wildlife conflict, we synthesized 15 years of ecological and ethnographic data from Ikh Nart Nature Reserve in Mongolia's Gobi steppe. The density of argali (Ovis ammon), the world's largest wild sheep, at Ikh Nart was among the highest in Mongolia, yet livestock were >90% of ungulate biomass and dogs >90% of large‐carnivore biomass. For argali, pastoral activities decreased food availability, increased mortality from dog predation, and potentially increased disease risk. Isotope analyses indicated that livestock accounted for >50% of the diet of the majority of gray wolves (Canis lupus) and up to 90% of diet in 25% of sampled wolves (n = 8). Livestock composed at least 96% of ungulate prey in the single wolf pack for which we collected species‐specific prey data. Interviews with pastoralists indicated that wolves annually killed 1–4% of Ikh Nart's livestock, and pastoralists killed wolves in retribution. Pastoralists reduced wolf survival by killing them, but their livestock were an abundant food source for wolves. Consequently, wolf density appeared to be largely decoupled from argali density, and pastoralists had indirect effects on argali that could be negative if pastoralists increased wolf density (apparent competition) or positive if pastoralists decreased wolf predation (apparent facilitation). Ikh Nart's argali population was stable despite these threats, but livestock are increasingly dominant numerically and functionally relative to argali. To support both native wildlife and pastoral livelihoods, we suggest training dogs to not kill argali, community insurance against livestock losses to wolves, reintroducing key native prey species to hotspots of human–wolf conflict, and developing incentives for pastoralists to reduce livestock density.     

Mitochondrial DNA analysis of native and selectively inbred Chesapeake Bay oysters,Crassostrea virginica

Mitochondrial DNA (mtDNA) genotypes were examined in 1989 in threeCrassostrea virginica (Gmelin) populations native to Chesapeake Bay, USA, and in one population selectively inbred for rapid growth for ten generations. We wished to determine whether this character would be useful as a genetic marker for distinguishing between the inbred line and the native oysters and to determine whether detectable genetic differences exist among present-day native populations ofC. virginica. Thirty mtDNA haplotypes were identified. The average percentage nucleotide difference between native haplotypes was 1.8%. Inbred oysters were characterized by mtDNA haplotypes distinctly different from ancestral native oysters, indicating a high degree of genetic differentiation between the two groups (average percentage mtDNA nucleotide sequence divergence,=21.8%). The common native haplotype was not present in the selectively inbred sample, and six of the seven haplotypes detected in the inbred oysters were not found in the survey of native oysters. Chi-square tests on haplotype frequencies indicated that the native populations were not significantly different from one another. However, the distribution and relatedness of haplotypes suggest that significant change in the oyster gene pool may have occurred over the past few decades.     

Developing Metapopulation Connectivity Criteria from Genetic and Habitat Data to Recover the Endangered Mexican Wolf

Restoring connectivity between fragmented populations is an important tool for alleviating genetic threats to endangered species. Yet recovery plans typically lack quantitative criteria for ensuring such population connectivity. We demonstrate how models that integrate habitat, genetic, and demographic data can be used to develop connectivity criteria for the endangered Mexican wolf (Canis lupus baileyi), which is currently being restored to the wild from a captive population descended from 7 founders. We used population viability analysis that incorporated pedigree data to evaluate the relation between connectivity and persistence for a restored Mexican wolf metapopulation of 3 populations of equal size. Decreasing dispersal rates greatly increased extinction risk for small populations (<150–200), especially as dispersal rates dropped below 0.5 genetically effective migrants per generation. We compared observed migration rates in the Northern Rocky Mountains (NRM) wolf metapopulation to 2 habitat‐based effective distance metrics, least‐cost and resistance distance. We then used effective distance between potential primary core populations in a restored Mexican wolf metapopulation to evaluate potential dispersal rates. Although potential connectivity was lower in the Mexican wolf versus the NRM wolf metapopulation, a connectivity rate of >0.5 genetically effective migrants per generation may be achievable via natural dispersal under current landscape conditions. When sufficient data are available, these methods allow planners to move beyond general aspirational connectivity goals or rules of thumb to develop objective and measurable connectivity criteria that more effectively support species recovery. The shift from simple connectivity rules of thumb to species‐specific analyses parallels the previous shift from general minimum‐viable‐population thresholds to detailed viability modeling in endangered species recovery planning. Desarrollo de Criterios de Conectividad Metapoblacional a Partir de Datos Genéticos y de Hábitat para Recuperar al Lobo Mexicano en Peligro de Extinción     

Patterns of Genetic Diversity in Remaining Giant Panda Populations

Abstract: The giant panda ( Ailuropoda melanoleuca ) is among the more familiar symbols of species conservation. The protection of giant panda populations has been aided recently by the establishment of more and better-managed reserves in existing panda habitat located in six mountain ranges in western China. These remaining populations are becoming increasingly isolated from one another, however, leading to the concern that historic patterns of gene flow will be disrupted and that reduced population sizes will lead to diminished genetic variability. We analyzed four categories of molecular genetic markers (mtDNA restriction-fragment-length polymorphisms [RFLP], mtDNA control region sequences, nuclear multilocus DNA fingerprints, and microsatellite size variation) in giant pandas from three mountain populations (Qionglai, Minshan, and Qinling) to assess current levels of genetic diversity and to detect evidence of historic population subdivisions. The three populations had moderate levels of genetic diversity compared with similarly studied carnivores for all four gene measures, with a slight but consistent reduction in variability apparent in the smaller Qinling population. That population also showed significant differentiation consistent with its isolation since historic times. From a strictly genetic perspective, the giant panda species and the three populations look promising insofar as they have retained a large amount of genetic diversity in each population, although evidence of recent population reduction—likely from habitat loss—is apparent. Ecological management to increase habitat, population expansion, and gene flow would seem an effective strategy to stabilize the decline of this endangered species.     

Biological, Conservation, and Ethical Implications of Exploiting and Controlling Wolves

The widespread claim that wolf populations can withstand 25–50% or greater annual reductions without major biological consequences is based primarily on the observation that populations often maintain their size from year to year as harvest or control continues or recover within a few years afterward. This emphasis on numerical status overlooks the likelihood of major, lingering impacts on the size, number, stability, and persistence of family-group social units, on reproductive, hunting, and territorial behavior, on the role of learning and related traditions, on within- and between-group patterns of genetic variation, and on overall mortality rates. The tendency of biologists and agencies in northern North America to promote wolf harvests that are four to eight times greater than ungulate harvests, in accord with the wolf versus ungulate difference in reproductive rates but contradictory to a broad array of differences in social organization and related behavior, is reason enough to question the logic of this prevailing management view. True sustained-yield management requires more emphasis on qualitative biological features to determine the extent to which wolves and other species with evolutionary histories as predators rather than as prey should be harvested. Most recent government-sponsored wolf control programs and proposals, including sterilization, relocation, and "redirected" killing, have been based on questionable claims about ungulate or livestock problems and have not adequately considered potential biological costs (especially to the target wolf populations), benefits, or management alternatives. The high sentience of wolves justifies overlapping biological-ethical concerns about such programs and especially about the heavy, indiscriminate, deceptively reported public hunting and trapping of wolves that is currently permitted throughout most of Alaska (U.S.A.)—including in national parks—and elsewhere.     

Inbreeding Depression in a Captive Wolf (Canis lupus) Population

Abstract. Uncertainty currently exists regarding the extent to which mammalian carnivores suffer from inbreeding depression. In particular, it has been proposed that wolves and species with a similar social structure are adapted to close inbreeding. Empirical data, however, are scarce. This paper provides strong evidence against the contention that natural populations of wolves are resistant to inbreeding depression. We analyzed studbook data of a captive wolf population bred in Scandinavian zoos and found negative effects of inbreeding expressed as reductions in juvenile weight, reproduction, and longevity. The occurrence of an apparently bereditary form of blindness is also associated with inbreeding. Different effects of inbreeding can be attributed to genes originating from different founder pairs, thus indicating that alleles that are deleterious in the homozygous state are fairly common in natural wolf populations.