Postglacial recolonisation of Lemmus lemmus in Fennoscandia (Funded by the Swedish Research Council & CLIMIGRATE)
The Norwegian lemming (Lemmus lemmus) is a cold-adapted rodent species, endemic to alpine shrub and grasslands in Fennoscandia. In this project I am investigating the origin of L. lemmus and test the habitat tracking hypothesis during the Pleistocene-Holocene transition. Ancient DNA techniques are used to retrieve mtDNA sequences from Late Pleistocene Lemmus sp. fossil remains, which are compared with genetic data from modern lemming populations. The results will indicate whether the species descends from glacial mid-latitude European populations that recolonised Fennoscandia after the ice melted, and thus tracked the tundra habitat as it shifted northwards, or from northern populations that were able to persist the last glacial maximum in a local Scandinavian refugium. A third alternative hypothesis, where post-glacial recolonisation originates from Siberia, has previously been rejected due to too large genetic distances between current L. lemmus and L. sibiricus populations.
Fate of the glacial populations of Lagopus muta and L. lagopus in Europe (Funded by the Centre for Ecology and Evolution & CLIMIGRATE)
This project will, just as the former, examine the ability of populations to track changes in habitat availability. Here I am studying Rock and Willow Ptarmigan (L. muta & L. lagopus), two ground dwelling grouse species that are currently restricted to northern and alpine regions. During the Late Pleistocene period however, the genus had an expanded distribution covering more southern and lowland ranges than today. I am analysing genetic variation within the mitochondrial control region in European Lagopus sp. fossil remains in order to investigate the fate of the glacial populations that inhabited most of mid-latitude Europe. By comparing these results with sequence data from extant European populations of L. muta and L. lagopus I test the hypothesis that the widespread glacial population managed to track its habitat as it shifted to northern and alpine regions, subsequently founding our modern European Lagopus sp. populations. A contrasting hypothesis is that the glacial fossil remains represent lineages that went extinct during the onset of Holocene, and that our modern Lagopus sp. populations have been established by post-glacial immigrants from the Beringian population in Siberia. A third alternative could be that the northern populations of Lagopus sp., just as proposed for lemmings, managed to survive in a local Scandinavian refugium.
Temporal changes in demography, population divergence and speciation in the genus Lemmus (Funded by the Swedish Research Council & CLIMIGRATE)
True lemmings (Lemmus lemmus, L. sibiricus and L. trimucronatus) are distributed throughout large parts of the Arctic, inhabiting humid shrub- and grasslands. In the Late Pleistocene the extent and distribution of this type of habitat varied greatly, both as a direct response to the temperature fluctuations as well the advance and retreat of the Eurasian and North American ice sheets. This project uses ancient DNA techniques to study the population history of true lemmings by conducting large-scale analyses of Lemmus sp. fossils from throughout the genus’ global distribution, spanning a time depth from 0 – 50 thousand years ago. The resulting genetic data is used to estimate changes in effective population size through time and identify range shifts, contractions and local population extinctions. Through an internal calibration of the molecular clock we will also be able to do more accurate estimates of divergence times pre-dating the limits of radiocarbon dating. By combining the genetic dataset with climatic data, analyses will be made of possible links between Late Pleistocene climatic fluctuations and demographic events in Lemmus sp. Questions addressed in the project include the timing of speciation within the genus, as well as when and where intra-specific phylogeographic groups evolved and what effect the millennial-scale warm periods had on populations.
Supervisor: Dr Love Dalén (Swedish Museum of Natural History, Stockholm)
Co-supervisor: Prof. Anders Angerbjörn (Department of Zoology, Stockholm University)
2009 - present.....PhD student, Swedish Museum of Natural History
2009 ....................Field assistant, Uppsala University
2008 - 2009.........Laboratory assistant, Uppsala University
2004 - 2009.........M.Sc in Biology, Uppsala University
2010 Riksmusei Vänner & René & Ebba Malaises Stiftelse
2010 Siftelsen A. Hambergs testamentsfond, Royal Swedish Academy of Sciences
2010 Stiftelsen Margit Althins Stipendiefond, Royal Swedish Academy of Sciences
Lagerholm VK, Sandoval-Castellanos E, Ehrich D, Abramson NI, Nadachowski A, Kalthoff DC, Germonpré M, Angerbjörn A, Stewart JR, Dalén L. (2014) On the origin of the Norwegian lemming. Molecular Ecology, 23: 2060-2071.