A beacon of dung: using lemming (Lemmus lemmus) winter nests and DNA analysis of faeces to further understand predator–prey dynamics in Northern Sweden

The hypothesis that predation is the cause of the regular small rodent population oscillations observed in boreal and Arctic regions has long been debated. Within this hypothesis, it is proposed that the most likely predators to cause these destabilizing effects are sedentary specialists, with small mustelids being possible candidates. One such case would be the highly specialized least weasel (Mustela nivalis) driving the Norwegian lemming (Lemmus lemmus) cycle in Fennoscandia. These predators are often elusive and therefore distribution data can only be based on field signs, which is problematic when various mustelid species are sympatric, such as weasels and stoats (Mustela erminea). Here we present the results of using mustelid faeces in predated winter lemming nests to correctly identify the predator and thus discern which species exerts the strongest predation pressure on lemming winter populations. Samples were obtained during different phases in the lemming cycle, spanning 6 years, to account for different prey densities. Faecal mitochondrial DNA extraction and amplification of a 400-bp fragment was successful in 92/114 samples (81%); the sequencing of these samples proved that most predation occurrences (83%) could be attributed to the least weasel. These findings support the hypothesis that weasels in particular show high specificity in predation and could therefore be candidates to driving the lemming cycle in this area. We conclude that DNA analysis of faecal remains around predated nests can be a useful tool for further investigations concerning predator–prey interactions in the tundra.

A new Norwegian Lemming subspecies from Novaya Zemlya, Arctic Russia

Norwegian Lemming Lemmus lemmus is a remarkable population cycling species having a number of aposematic traits in coloration and behavior. This species was thought to be the only mammal endemic to Fennoscandia. Here, we report on the discovery of a distinct lineage of this species from Novaya Zemlya. This lineage is described here as the new subspecies Lemmus lemmus chernovi ssp. nov. that morphologically differs from the nominate subspecies by having a cryptic coloration. Our time-calibrated phylogeny revealed that this insular subspecies was isolated there since the Eemian interglacial (mean age 93 Ka). Hence, bright coloration and antipredator behavior of the nominate subspecies are novel aposematic traits that evolved since its isolation in a European refugium. This new discovery indicates that Novaya Zemlya supported a cryptic polar refugium for cold-adapted terrestrial fauna during the Pleistocene. Finally, our findings highlight that allopatric ranges of the true lemmings (Lemmus) reflect stepwise range expansions in cold climatic episodes with subsequent isolation in refugia during interglacial events.