Population turnover and speciation in the genus Dicrostonyx during the Late Pleistocene
The Late Pleistocene has experienced many rapid and severe climatic changes that are believed to have influenced the demography and genetic diversity of many species. Collared lemmings (Dicrostonyx sp.) are small herbivorous rodents that have a preference for cold and dry habitats and exhibit a nearly holarctic distribution with the exception of Scandinavia. Previous phylogenetic studies on contemporary lemmings have found low genetic variation, indicative of historical events such as population bottlenecks and population fragmentation. The recovery of radiocarbon-dated fossil material up to 50,000 years old from their widespread geographic range allows me to examine such events in real time. I use ancient DNA techniques and phylogenetic methods to detect changes in effective population size and accurately estimate divergence times. My results are combined to paleoclimatic data to investigate whether past climate changes affected the population dynamics of the genus, as well as to appraise the importance of glacial or interglacial periods for the occurrence of speciation events in the genus. Back-casted distrubution models will then be developed in order to assess the accuracy of such models in predicting whether populations move or become extinct when faced with climate change.
Temporal and spatial variation in the feeding niche of small rodents
The hypothesis that climate change has affected the diet of small herbivorous rodents is being evaluated in this project. Habitat alterations following climate change set different selective pressures to local populations that are believed to respond through adaptation, move or become extinct. I use faecal samples from contemporary lemmings and voles as well as from fossilized coprolites in order to identify changes in their dietary composition across space and time. I collect contemporary faecal samples from the Scandinavian mountain tundra every summer, while Late Pleistocene lemming coprolites are already collected from the Ural Mountains. I extract and analyse plant DNA to retrieve information about the diet along with mtDNA to identify from which species each faecal sample derives from. Differences in the diet among species and between regions and years will be revealed from the contemporary genetic data, providing information about inter-specific resource competition as well as about a possible relationship between diet and small rodent population cycles. Genetic data from the Late Pleistocene coprolites will demonstrate potential long-term changes in the diet that may be associated and explained by well documented climate changes during the time period up to the Pleistocene/ Holocene transition
Genetic drift and selection in the Wrangel island mammoth population
The woolly mammoth (Mammuthus primigenius) was a prevalent species of the Megafauna that lived during the Pleistocene in the Northern hemisphere and became extinct around 10,000 years ago from mainland Eurasia and North America. However, a small population managed to persist and survive on the Wrangel Island in the Arctic Ocean until its final disappearance at around 3,500 years before present. In this project I focus on the Wrangel Island mammoth population to examine the microevolutionary processes that occurred during the time period from the isolation of the island, as sea levels rose, until the final extinction event. I will generate and analyse SNP data (single-nucleotide polymorphisms) from radio-carbon dated fossil material between 9,000 and 3,500 years old, collected on Wrangel Island, in order to evaluate the level of genetic drift and identify potential selective forces that have acted on their genome, over time.
Supervisor: Dr Love Dalén (Swedish Museum of Natural History)
Co-supervisors: Assist. Prof. Anders Götherström (Dept. of Evolutionary Biology, Uppsala University),
Prof. Olof Leimar (Dept. of Ethology, Stockholm University).
High-density linkage mapping of the Z-chromosome in the Ficedula species
Chromosomal speciation models suggest that chromosomal rearrangements such as inversions promote reproductive isolation between diversifying populations, potentially leading to speciation. The black and white European flycatchers (Ficedula albicollis and Ficedula hypoleuca) are two closely related species that have diverged at approximately 1-2 million years ago and produce hybrids with low viability in two sympatric regions in Central Europe and the Baltic islands of Gotland and Öland. For my MSc project I tested the hypothesis that chromosomal rearrangements on the sex chromosome of the collared and the pied flycatcher have acted as reproductive barriers between the two species. High-coverage, gene-based linkage maps of the Z-chromosome of the two Ficedula species were developed and evaluated in a comparative context. Extensive co-linearity was apparent together with no evidence for chromosomal rearrangements, implying that other factors are responsible for the high degree of reproductive isolation observed between the two species.
Supervisor: Prof. Hans Ellegren (Dept. Of Evolutionary Biology, Uppsala University).
April 2010 - Jan 2015....PhD in Molecular Systematics and Evolution, Swedish Museum of Natural History.
Sept 2009 - Mar 2010...Research Assistant, Dept. of Evol. Biol., Uppsala University
Aug 2009 - Sept 2009...Research Assistant, Dept. of Pop.& Cons. Biol., Uppsala Uni.
Aug 2007 - July 2009....M.Sc in Biology, Uppsala University
Sep 2001 - Feb 2006.....B.Sc in Biology, Aristotle University of Thessaloniki.
Skoglund P, Ersmark E, Palkopoulou E, Dalén L. (2015) Ancient wolf genome reveals an early divergence of domestic dog ancestors and admixture into high-latitude breeds. Current Biology, 25: 1515–1519.
Palkopoulou E, Mallick S, Skoglund P, Enk J, Rohland N, Li H, Omrak A, Vartanyan S, Poinar H, Götherström A, Reich D, Dalén L. (2015) Complete genomes reveal signatures of demographic and genetic declines in the woolly mammoth. Current Biology, 25, 1395–1400.
Tison JL, Blennow V, Palkopoulou E, Gustafsson P, Roos A, Dalén L. (2015) Population structure and recent temporal changes in genetic variation in Eurasian otters from Sweden. Conservation Genetics, 16: 371–384.
Sandoval-Castellanos E, Palkopoulou E, Dalén L. (2014) Back to BaySICS: a user-friendly program for Bayesian statistical inference from coalescent simulations. PLoS ONE, 9: e98011.
Cappellini E, Gentry A, Palkopoulou E, Ishida Y, Cram D, Roos AM, Watson M, Johansson US, Fernholm B, Agnelli P, Barbagli F, Littlewood DTJ, Kelstrup CD, Olsen JV, Lister AM, Roca AL, Dalén L, Gilbert MTP. (2014) Resolution of the type material of the Asian elephant, Elephas maximus (Proboscidea: Elephantidae) Linnaeus, 1758. Zoological Journal of the Linnean Society, 170: 222–232.
Palkopoulou E, Dalén L, Lister AM, Vartanyan S, Sablin M, Sher A, Nyström Edmark V, Brandström MD, Germonpré M, Barnes I, Thomas JA. (2013). Holarctic genetic structure and range dynamics in the woolly mammoth. Proceedings of the Royal Society B, 280.
Brace S *, Palkopoulou E *, Dalén L, Lister AM, Miller R, Otte M, Germonpré M, Blockley SPE, Stewart JR, Barnes I. (2012) Serial population extinctions in a small mammal indicate Late Pleistocene ecosystem instability. PNAS, 109: 20532-36.
Backström N.* Palkopoulou E.* Qvarnström A. and Ellegren H. No evidence for Z-chromosome rearrangements between the pied flycatcher and the collared flycatcher as judged by gene-based comparative genetic maps. Molecular Ecology 19(16): 3394-3405.
Backström N., Lindell J., Zhang Y., Palkopoulou E., Qvarnström A., Sætre G.P. and Ellegren H. A high density scan of the Z-chromosome in Ficedula flycatchers reveals candidate loci for diversifying selection. Evolution 64(12): 3461- 3475.
* These authors contributed equally to this study.