Genetic variation in lowland and mountain populations of Tofieldia calyculata and their ability to survive within low levels of genetic diversity

Loss of genetic diversity is expected to be a reason behind the decline of populations of many rare species. To what extent this is true for populations at the range periphery remains to be explored. Alpine species with peripheral lowland populations are an ideal but little-known model system to address this issue. We used 17 microsatellite markers to investigate the genetic diversity and structure of populations of Tofieldia calyculata, a common species in central European mountains, but highly endangered in lowlands. We showed that lowland populations have lower genetic diversity than mountain populations and that the two groups of populations are not clearly differentiated genetically. The species probably survived the last glaciation in refugia in the margins of the Alps and the western Carpathians and some lowland populations likely originated by postglacial colonisation. Some lowland populations may be relictual, but our data did not unequivocally confirm this. Low genetic diversity of lowland populations is likely the result of the reduction of population sizes, limited gene flow, and selfing. Based on data from herbarium specimens from extinct lowland populations, within-population genetic diversity has not changed over the last century suggesting that, under suitable habitat conditions, these populations are able to survive with low levels of genetic diversity. This idea is also supported by the presence of large viable extant populations with very low genetic diversity. Comparisons between modern and historic collection also showed that a large proportion of genetic diversity was lost, due mainly to the extinction of whole populations. Our results provided detailed insight into the recent past of the populations of Tofieldia calyculata, but the genetic diversity of the populations before the twentieth century remains unknown due to the poor quality of old DNA from herbaria samples. Overall, the study indicates that despite reduced genetic diversity, the lowland populations harbour some unique alleles and, with the current levels of genetic diversity, have a chance to survive in the long-term, and thus deserve conservation.