Lindsey Carmichael

Prey specialization may influence patterns of gene flow in wolves of the Canadian Northwest

This study characterizes population genetic structure among grey wolves (Canis lupus) in northwestern Canada, and discusses potential physical and biological determinants of this structure. Four hundred and ninety‐one grey wolves, from nine regions in the Yukon, Northwest Territories and British Columbia, were genotyped using nine microsatellite loci. Results indicate that wolf gene flow is reduced significantly across the Mackenzie River, most likely due to the north–south migration patterns of the barren‐ground caribou herds that flank it. Furthermore, although Banks and Victoria Island wolves are genetically similar, they are distinct from mainland wolf populations across the Amundsen Gulf. However, low‐level island–mainland wolf migration may occur in conjunction with the movements of the Dolphin‐Union caribou herd. Whereas previous authors have examined isolation‐by‐distance in wolves, this study is the first to demonstrate correlations between genetic structure of wolf populations and the presence of topographical barriers between them. Perhaps most interesting is the possibility that these barriers reflect prey specialization by wolves in different regions.

Historical and ecological determinants of genetic structure in arctic canids

Wolves (Canis lupus) and arctic foxes (Alopex lagopus) are the only canid species found throughout the mainland tundra and arctic islands of North America. Contrasting evolutionary histories, and the contemporary ecology of each species, have combined to produce their divergent population genetic characteristics. Arctic foxes are more variable than wolves, and both island and mainland fox populations possess similarly high microsatellite variation. These differences result from larger effective population sizes in arctic foxes, and the fact that, unlike wolves, foxes were not isolated in discrete refugia during the Pleistocene. Despite the large physical distances and distinct ecotypes represented, a single, panmictic population of arctic foxes was found which spans the Svalbard Archipelago and the North American range of the species. This pattern likely reflects both the absence of historical population bottlenecks and current, high levels of gene flow following frequent long‐distance foraging movements. In contrast, genetic structure in wolves correlates strongly to transitions in habitat type, and is probably determined by natal habitat‐biased dispersal. Nonrandom dispersal may be cued by relative levels of vegetation cover between tundra and forest habitats, but especially by wolf prey specialization on ungulate species of familiar type and behaviour (sedentary or migratory). Results presented here suggest that, through its influence on sea ice, vegetation, prey dynamics and distribution, continued arctic climate change may have effects as dramatic as those of the Pleistocene on the genetic structure of arctic canid species.

Pulses of movement across the sea ice: population connectivity and temporal genetic structure in the arctic fox

Lemmings are involved in several important functions in the Arctic ecosystem. The Arctic fox (Vulpes lagopus) can be divided into two discrete ecotypes: “lemming foxes” and “coastal foxes”. Crashes in lemming abundance can result in pulses of “lemming fox” movement across the Arctic sea ice and immigration into coastal habitats in search for food. These pulses can influence the genetic structure of the receiving population. We have tested the impact of immigration on the genetic structure of the “coastal fox” population in Svalbard by recording microsatellite variation in seven loci for 162 Arctic foxes sampled during the summer and winter over a 5-year period. Genetic heterogeneity and temporal genetic shifts, as inferred by STRUCTURE simulations and deviations from Hardy–Weinberg proportions, respectively, were recorded. Maximum likelihood estimates of movement as well as STRUCTURE simulations suggested that both immigration and genetic mixture are higher in Svalbard than in the neighbouring “lemming fox” populations. The STRUCTURE simulations and AMOVA revealed there are differences in genetic composition of the population between summer and winter seasons, indicating that immigrants are not present in the reproductive portion of the Svalbard population. Based on these results, we conclude that Arctic fox population structure varies with time and is influenced by immigration from neighbouring populations. The lemming cycle is likely an important factor shaping Arctic fox movement across sea ice and the subsequent population genetic structure, but is also likely to influence local adaptation to the coastal habitat and the prevalence of diseases.

Northwest passages: conservation genetics of Arctic Island wolves

Wolves in the Canadian Arctic Archipelago face several challenges to persistence: a harsh habitat, an unstable prey base, and potentially significant anthropogenic influences. These external factors, if combined with genetic constraints common to island populations, could be particularly difficult to withstand. To determine the genetic status of Arctic Island wolves, we used 14 microsatellite loci to estimate population variation and the extent of inter-island and island-mainland gene flow. All island populations were significantly less variable than mainland wolves; although inbreeding is currently insignificant, the two least variable populations, Banks and the High Arctic (Ellesmere and Devon Islands), showed genetic signatures of recent population declines. Recovery after a bottleneck appears to result, in large part, via recolonization from other islands. These extinction-recolonization dynamics, and the degree of similarity among island wolves revealed by Bayesian clustering, suggest that Arctic Island wolves function as a metapopulation. Persistence of the metapopulation may be supported by periodic migration from mainland populations, occurring primarily through two corridors: Baffin Island in the Eastern Arctic, and Victoria Island in the Western Arctic. This gene flow could be compromised or eliminated by loss—due to climatic warming or increased human activity—of sea ice in the Northwest Passage.

Genotyping of Pseudohermaphrodite Polar Bears in Nunavut and Advances in DNA Sexing Techniques

Abstract Female pseudohermaphroditism is characterized by gonads consistent with chromosomal sex combined with ambiguous, masculinized external genitalia. Recognized in many mammals, this condition results from fetal exposure to androgens that can be embryonic, maternal, or environmental in origin. Female pseudohermaphrodite black and brown bears (Ursus americanus and U. arctos) from Alberta, Canada, and polar bears (U. maritimus) from Svalbard, Norway, have been identified. Recent population surveys in Nunavut, Canada, led to the discovery of 11 additional female pseudohermaphrodite polar bears. Each bear was screened for the presence of sex-determining region-Y (Sry) and amelogenin-Y (AMELY) genes as indicators of Y-chromosome DNA. One bear possessed both genes, implying that trisomy or a chromosomal rearrangement may account for her virilized phenotype. Preliminary data suggested that Sry was also present in the other 10 bears; further testing disproved that result, revealed an important source of error when using polymerase chain reaction (PCR) to screen for the Sry gene, and led to the development of new amelogenin primers that provide superior sex information for bears. Ultimately, these extensive screens also supported the conclusion that 10 of 11 morphologically abnormal individuals may possess no genuine male-specific DNA. Therefore, nongenetic mechanisms such as maternal tumors, freemartinism, or endocrinological effects of environmental contaminants may also influence the development of the female pseudohermaphrodite phenotype in Nunavut polar bears.

Age-dependent genetic structure of arctic foxes in Svalbard

Arctic foxes are highly mobile arctic predators with a very weak population genetic structure over large parts of their range. Less is, however, known about the more local genetic structure within regions. Here, we analyze genotypes at 12 microsatellite loci for 561 arctic foxes trapped in the high-arctic archipelago Svalbard and investigate the genetic structure in three different age classes. Significant linkage disequilibrium, deficit of heterozygotes, genetic differentiation, and a decrease in relatedness with distance among animals trapped in their first winter suggested that some litter mates remain in proximity of each other during the first winter. This pattern was stronger for females than for males, indicating male-biased juvenile dispersal, and weaker for older animals. There was no genetic differentiation among adult foxes harvested in different hunting areas. The foxes from the protected area around Hornsund were however more differentiated than expected based on geographic distance alone, suggesting a possible disrupting effect of harvest on the spatial genetic structure in the rest of Svalbard. Our results also indicated a possible kin structure among adult females, suggesting natal philopatry, but further investigations will be needed to reach firm conclusions concerning kin structure in arctic foxes.