Studies of declining populations - temporal genetic analyses of two arctic mammals

Abstract: Many populations and species are threatened with extinction today. Understanding the extinction process and the factors behind population decline is therefore important. In this thesis, genetic analyses were performed on temporally spaced samples to investigate the demographic history and genetic effects of population reduction of two species: the arctic fox (Vulpes lagopus) and the woolly mammoth (Mammuthus primigenius). We used ancient DNA techniques to measure genetic variation in both mitochondrial DNA and microsatellites. In paper I, we investigated the genetic consequences of a human-induced demographic bottleneck in the Scandinavian arctic fox population. By comparing genetic data from museum specimens with genetic data from the contemporary population, we found a loss of genetic variation. However, the loss was less than expected, probably due to gene flow from North Russia. Using the same approach, we also found that Pleistocene arctic foxes from midlatitude Europe do not seem to have contributed to the genetic composition of contemporary populations (paper II). This suggests that they went extinct rather than track their habitat when it shifted northwards at the end of Pleistocene. Further, by analysing genetic data from radiocarbon dated fossils, we also found that the woolly mammoth lost genetic variation in connection to a marked decline in population size at the end of Pleistocene (paper III and IV). However, no further losses were detected during the time that mammoths were isolated on Wrangel Island, which suggests a rapid extinction process possibly caused by the arrival of humans or a short-term change in climate (paper III and IV). The results in this thesis demonstrate the usefulness of temporal genetic analyses for identifying population decline and evaluating its consequences.