Review of microsatellites in ecology and parentage analysis of Norwegian beavers (Castor fiber) based on cross-specific microsatellites

Abstract

The Eurasian Beaver (Castor fiber) in Scandinavia was once close to extinction due to a bottleneck resulting from vigorous overhunting in the middle of the 19th century. After measures of protection, the population number increased again until it reached a level that brought it into the focus of ecological research and monitoring. Molecular ecology has advanced rapidly over the last decades, and molecule markers like microsatellites have become a powerful tool for such genetic population analyses and monitoring. In this study a set of nine microsatellite pairs designed for the North American beaver (Castor canadensis) is used to analyze parentage in a Eurasian beaver population in Telemark, Norway. To this purpose, DNA was extracted from 148 hair samples. Microsatellite genotypes at five variable loci were obtained from 136 of the 148 extracted DNA samples. Based on previously collected observation data, 50 parent-offspring relationships were constructed from the 136 genotyped individuals. By using the parentage exclusion method, there were found 16 cases of mismatching genotypes between an offspring and a parent or parent pair. These results suggest that extra-pair mating might have occurred in the genotyped beaver population. However, the acceptance of the exclusions proved difficult since 13 out of 16 exclusions were based on homozygous genotypes. The derivation from Hardy Weinberg equilibrium and the low heterozygosity of the microsatellite loci used in this study indicated the presence of null alleles which might have lead to false homozygotes suggesting that further genetic analyses might be necessary for successful parentage analysis.