Microsatellite analysis of population structure in Canadian polar bears

TLDR

Genetic population structure studies in large mammals are hampered by low genetic variation, especially in polar bears. The study aims to use eight hypervariable microsatellite loci to examine genetic relationships among four Canadian polar bear populations. Eight microsatellite loci were genotyped across individuals from the northern Beaufort Sea, southern Beaufort Sea, western Hudson Bay, and Davis Strait–Labrador Sea to assess relationships. The loci revealed ~60 % heterozygosity within populations, significant allele frequency differences among all population pairs, genetic distances reflecting geography but also unexpected gene‑flow patterns, and enabled accurate assignment of individuals to their region of origin, indicating restricted gene flow despite long‑distance movements.

Abstract

Abstract Attempts to study the genetic population structure of large mammals are often hampered by the low levels of genetic variation observed in these species. Polar bears have particularly low levels of genetic variation with the result that their genetic population structure has been intractable. We describe the use of eight hypervariable microsatellite loci to study the genetic relationships between four Canadian polar bear populations: the northern Beaufort Sea, southern Beaufort Sea, western Hudson Bay, and Davis Strait ‐ Labrador Sea. These markers detected considerable genetic variation, with average heterozygosity near 60% within each population. Interpopulation differences in allele frequency distribution were significant between all pairs of populations, including two adjacent populations in the Beaufort Sea. Measures of genetic distance reflect the geographic distribution of populations, but also suggest patterns of gene flow which are not obvious from geography and may reflect movement patterns of these animals. Distribution of variation is sufficiently different between the Beaufort Sea populations and the two more eastern ones that the region of origin for a given sample can be predicted based on its expected genotype frequency using an assignment test. These data indicate that gene flow between local populations is restricted despite the long‐distance seasonal movements undertaken by polar bears.