Genetic consequences of population decline in the European otter (Lutra lutra): an assessment of microsatellite DNA variation in Danish otters from 1883 to 1993

The European otter (Lutra lutra) was common in Denmark until the 1960s, but its present distribution encompasses only a minor part of the country. The aim of this study was to assess whether the recent population decline has resulted in loss of genetic variability and to gain further insight into the dynamics of the population decline. This was done by analysing microsatellite DNA variation in contemporary and historical samples, the latter encompassing DNA samples extracted from museum specimens covering a time-span from the 1880s to the 1960s. Tests for differences in expected heterozygosity and the numbers of alleles in contemporary versus historical samples and a test for detecting population bottlenecks provided few indications of a recent bottleneck and loss of variability. However, a procedure for detecting population expansions and declines, based on the genealogical history of microsatellite alleles, suggested that a drastic long-term population decline has taken place, which could have started more than 2000 years ago, possibly due to ancient anthropogenic pressure. Finally, assignment tests and pairwise F(ST) values suggested weak but statistically significant genetic differentiation between the extant population and historical samples of otters from other regions in Denmark, more likely reflecting differentiation among original populations rather than recent drift.