Evaluating a putative bottleneck in a population of bowhead whales from patterns of microsatellite diversity and genetic disequilibria

A size-selected Balaena mysticetus genomic library was screened for clones containing simple sequence repeat, or microsatellite, loci. A total of II n ovel loci was identified. These loci were combined with a set of 9 publishe d loci, for a total of 20 markers, and were scored across a sample of 108 b owhead whales from the Bering-Chukchi-Beaufort Seas population of bowhead w hales. Genetic variability was measured in terms of polymorphism informatio n content values and unbiased heterozygosity. From the latter, estimates of long-term effective population size were obtained. In addition, gametic ph ase disequilibrium among loci was investigated. Moderate to high levels of polymorphism were found overall, and the long-term effective size estimates were large relative to total population size. Tests of heterozygosity exce ss (Cornuet and Luikart 1996) and allele frequency distribution (Luikart et al. 1998) indicated that the possibility of a recent genetic bottleneck in the Bering-Chukchi-Beaufort Seas population of bowhead whales is highly un likely. However, the fact that five loci displayed a statistically signific ant heterozygote deficiency remains to be explained.