Local adaptation and gene flow in Empetrum hermaphroditum, a keystone species of boreal-arctic ecosystems, along an altitudinal stress gradient
Final Report Abstract
Plants may respond to changes in the abiotic and biotic conditions though (i) shifts in phenology (ii) range shifts and/or (iii) in situ change of morphological or physiological traits. In arctic-alpine areas snow cover, which may last for over 8 months, represents a strong selection factor with significant effects on the distribution and abundance of plant species and communities. Owing to increasing temperatures, winter snow depth is predicted to increase but snow duration will decease owing to warm spells in late winter/early spring. For a better understanding of potential responses of plant species to these rapidly changing conditions, we need more knowledge concerning the effects of driving environmental factors on plant growth, distribution and abundance. The topography within arctic-alpine landscapes is very heterogeneous, resulting in diverse snow distribution patterns, with different snow depth during winter and differences in snowmelt timing in spring. Therefore, we used these natural gradients to study how local adaptation, shoot growth, flowering phenology, population genetic structure and clonal structure of Empetrum hermaphroditum varied among three habitats, i.e. exposed ridges, sheltered depressions and birch forest. Furthermore, we analysed if the observed patterns were consistent across four different study areas, varying in latitude (Northern Sweden vs. Central Norway) and climate (sub-oceanic vs. sub-continental). Unfortunately, the planned reciprocal transplant experiment for the analysis of local adaptation had to be discarded because collected ramets did not root both under common garden conditions in Abisko and under controlled glasshouse conditions in Giessen. With respect to morphological plasticity, there were significant differences in shoot growth between deep snow cover and shallow snow cover habitats with longer shoot growth and higher biomass production in deep snow cover habitats. Shoots in shallow snow cover habitats were characterised by significantly denser leaf packing. Interestingly, our two-year observations from different regions demonstrated that despite consistently and significantly earlier snowmelt in exposed ridges, full flowering of Empetrum hermaphroditum was almost synchronous with that in birch forest habitats and low-alpine depressions with high winter snow accumulation. Such as high flowering overlap implies that gene flow is potentially possible between all three habitat types and that snow cover does not present a barrier to gene flow in the study species. Nevertheless, first results of the population genetic study indicate that despite weak barriers to gene flow there is clear genetic differentiation between the three habitats. Ongoing analyses will address genetic diversity of and the degree of gene flow between different habitats. The analysis of clonal structure showed higher genotype and clonal diversity on exposed ridges than in habitats with high winter snow accumulation, pointing to differences in sexual reproduction between habitat types. In conclusion, the results of the project demonstrate a consistent match between the growth and morphology of Empetrum hermaphroditum and the prevailing local habitat conditions. Owing to broad flowering overlap, winter snow accumulation does probably not present an efficient barrier to gene flow. Consequently, genetic differentiation between habitats is relatively low and there are no strong indications for local adaptation. High morphological plasticity suggests that the species has the potential to cope with changing snow conditions in the course of climate warming.
Publications
- (2013). How does flowering phenology and morphology of Empetrum hermaphroditum respond to changing snow cover regimes? - International Tundra Experiment ITEX - More than 20 years of tundra vegetation change research, Bergün (Switzerland)
Bienau, M.J., Hattermann, D., Kröncke, M., Otte, A., Eiserhardt, W.L., Eckstein, R.L.
- (2014). Snow cover consistently affects growth and reproduction of Empetrum hermaphroditum across latitudinal and local climatic gradients. Alpine Botany 124: 115-129
Bienau, M.J., Hattermann, D., Kröncke, M., Kretz, L., Otte, A., Eiserhardt, W.L., Milbau, A., Graae, B.J., Durka, W., Eckstein, R.L.
(See online at https://doi.org/10.1007/s00035-014-0137-8) - (2014). Spross-Morphologie, Blüh-Phänologie und lokale Adaptation bei Empetrum hermaphroditum, einer Schlüsselart boreal-arktischer Ökosysteme, entlang eines Schneedeckungsgradienten - Treffpunkt Biologische Vielfalt - Interdisziplinäre Wissenschaftstagung zur Biodiversitätsforschung im Rahmen des Übereinkommens über die biologische Vielfalt, Vilm (Germany)
Bienau, M.J., Hattermann, D., Kröncke, M., Kretz, L., Otte, A., Eiserhardt, W.L., Milbau, A., Graae, B.J., Durka, W., Eckstein, R.L.
- (2015). Local adaptation of Empetrum hermaphroditum to habitats with different snow cover - 1st Annual Meeting in Conservation Genetics – Science and Practice, Zürich-Birmensdorf (Switzerland)
Bienau, M.J., Jager, M., Otte, A., Durka, W., Eckstein, R.L.
- (2015). Spross-Morphologie, Blüh-Phänologie und lokale Adaptation bei Empetrum hermaphroditum, einer Schlüsselart boreal-arktischer Ökosysteme, entlang eines Schneedeckungsgradienten. BfN-Skripten 397: 107-112
Bienau, M.J., Hattermann, D., Kröncke, M., Kretz, L., Otte, A., Eiserhardt, W.L., Milbau, A., Graae, B.J., Durka, W., Eckstein, R.L.
- (2015). Synchronous flowering despite differences in snowmelt among habitats of Empetrum hermaphroditum. Acta Oecologica 69: 129-136
Bienau, M.J., Kröncke, M., Eiserhardt, W.L., Otte, A., Graae, B.J., Milbau, A., Durka, W., Eckstein, R.L.
(See online at https://doi.org/10.1016/j.actao.2015.10.005)
