Variation in Genetic Diversity across the Range of North American Brown Bears

Abstract

Understanding the factors that influence the rate at which natural populations lose genetic diversity is a central aspect of conservation genetics because of the importance of genetic diversity in maintaining evolutionary potential and individual fitness. Concerns about loss of genetic diversity are particularly relevant to large carnivores, such as brown bears ( Ursus arctos ), that are distributed at low densities and are highly susceptible to human-caused population fragmentation. We used eight highly variable nuclear microsatellite markers to study current levels of genetic variation across the North American range of brown bears. The highest levels of within-population genetic diversity ( H e ϭ 0.76) were found in northern populations in the core of the North American distribution. Diversity was significantly lower in populations at the southern fringe of the distribution, in the Northwest Territories, and in southwest Alaska. Diversity was lower still in the Yellowstone Ecosystem population ( H e ϭ 0.55), an isolated remnant of the larger distribution that recently extended south from the Canadian border into Mexico. The insular population on the Kodiak Archipelago had very low genetic diversity ( H e ϭ 0.26). The Yellowstone and Kodiak data suggest that the effective population size for brown bears is much smaller than previously suspected. These results indicate that the levels of diversity in most undisturbed populations can be maintained only through connections to populations on the scale of the current North American distribution. At the same time, the Kodiak data demonstrate that populations well under the size recommended for long-term conservation can persist and thrive for thousands of years, although the probability of such persistence remains unknown. Variación en la Diversidad Genética a lo largo del Rango de Distribución del Oso Café de NorteaméricaResumen: Entender los factores que influeyen en la tasa a la cual las poblaciones naturales pierden diversidad genética es un aspecto central de la genética de la conservación debido a la importancia de la diversidad genética en el mantenimiento del potencial evolutivo y la condición individual. Las preocupaciones sobre la pérdida de la diversidad genética tiene particular relevancia para los carnivoros mayores, como lo es el oso café ( Ursus arctos ), que se distribuye a bajas densidades y que es altamente susceptible a la fragmentación poblacional causada por humanos. Para estudiar los niveles actuales de variación genética a lo largo del rango de distribución de los osos cafés, usamos ocho marcadores microsatélite nucleares altamente variables. Los niveles mas altos de diversidad genética intrapoblacional ( H e ϭ 0.76) se encontraron en poblaciones del Norte en el centro de la distribución en Norteamérica. La diversidad fue significativamente menor en poblaciones limítrofes sureñas, en los territorios del Noroeste y el Suroeste de Alaska. La diversidad fue mas baja aún en la población de Yellowstone ( H e ϭ 0.55), un remanente de una distribución...

Non-invasive genetic study of the endangered Cantabrian brown bear (Ursus arctos)

“…For example, the degree of genetic differentiation is considerably higher than the values reported for pairwise comparisons among subpopulations in Scandinavia, where F st ranged between 0.01 and 0.14 and Nei's standard distance ranged between 0.03 and 0.38. The genetic distance between the two Cantabrian subpopulations, which are only 30 km apart, are comparable with the values reported for the most distant areas within the continuous distribution of brown bears in North America, which are several thousands of kilometres apart (Paetkau et al 1998). This result also shows that habitat discontinuities such as roads and farmland play a larger role in genetic substructuring of population than linear distance, which has also been seen in populations of Cross River gorilla (Bergl and Vigilant 2007).…”

“…The genetic diversity of the Cantabrian population is lower than in other bear populations considered to have a good conservation status (Paetkau et al 1998;Waits et al 1998) and is comparable with those found in Yellowstone (H e = 0.55; Paetkau et al 1998) and Deosai National Park (Pakistan) (H e = 0.55; Bellemain et al 2007). Yellowstone and Cantabrian populations have had a very similar history.…”

“…Yellowstone and Cantabrian populations have had a very similar history. Both populations have gone from being embedded in a very large continuous population to being an isolated remnant, separated from other brown bears for 300 years in the case of the Cantabrian population (Naves et al 1999) and 100 years for the Yellowstone population (Paetkau et al 1998). In both cases, there is no prospect of renewed connections with other populations.…”

Local seed dispersal in European silver fir (Abies alba Mill.): lessons learned from a seed trap experiment

“…It describes the probability that two randomly drawn (unrelated) individuals (p ID ) or siblings (p IDsibs ) exhibit identical multilocus genotypes (Paetkau et al 1998). Standard parameters of genetic variation and diversity were calculated for all loci based on individuals sampled in the forest stand and on the genotypes of the seed wings.…”

Introductions over introductions: the genomic adulteration of an early genetically valuable alien species in the United Kingdom

“…The discriminatory power of the whole set of STR loci was evaluated with GIMLET (v. 1.3.3: Valière 2002) by estimating the probability that two individuals drawn at random from the populations showed identical multilocus genotypes by chance (P ID and P ID sib: for the latter, we assumed sibling relationships) (Peatkau et al 1998;Waits et al 2001). We used (Hochberg 1988).…”