Tracking Holocene genetic diversity in the Swiss Alps using ancient DNA

The project focuses on the effects of past climatic and anthropogenic disturbances on four key tree species of Swiss mountain forests, i.e. Abies alba, Larix decidua, Picea abies and Pinus cembra. We will test palaeoecologically-inferred recolonization pathways in response to rapid and repeated temperature increases from the end of the last Ice Age to the Holocene warm period, by extracting and analysing aDNA from subfossil plant remains of the first populations that established around two lakes in the Swiss Alps. In order to find out if trees were able to adapt to climatic changes in the past, we will track adaptive and neutral genetic diversity through the Holocene by analyzing aDNA from time periods with marked demographic changes of the four focal species. We will also sample present-day tree populations, to link the aDNA genotypes with current genetic variation and identify cryptic lineages. The basis of this ambitious project will be the analysis of pollen, macrofossils and charcoal deposited in lake sediment archives to reconstruct local to regional vegetation and fire dynamics with high chronological precision and resolution. We will combine these palaeoecological analyses with a spatially explicit dynamic vegetation model (LandClim) to disentangle different forcing factors (i.e climate and anthropogenic land-use), test hypotheses regarding past demographic changes and simulate future vegetation dynamics under different climate and land-use scenarios.

Exploring the impact of past climatic change on the genetic diversity of Swiss mountain forests: combining paleoecological and paleogenetic approaches

Mountain forests are strongly affected by temperature and are expected to shift upslope with the current climate change, but little is known about the impact of such range shifts and altered selection pressures on the genetic diversity of tree populations. This new research project, funded by the SwissForestLab, will undertake large-scale ancient DNA analyses of subfossil tree remains to reveal for the first time the evolutionary responses of mountain tree populations to past climate change. The project focuses on the transition from the Younger Dryas to the Holocene (11’700 years ago), when temperatures markedly increased by 2–4°C within only a few decades, making it a close analogue to current and future climate warming. For the genetic analyses we will use tree remains such as needles and seeds that have been preserved in natural archives along an altitudinal gradient in the Southern Swiss Alps. The results will help to develop management strategies to maintain the adaptive potential and genetic diversity of mountain tree population under future climate change.

View of Gola di Lago, one of the study sites in the PaleoGenes project
View of Gola di Lago, one of the study sites in the PaleoGenes project © Christoph Schwörer