How glacial history and environmental variation affect population differentiation and gene flow dynamics in Alpine plant species

Abstract

How glacial history and environmental variation affect population differentiation and gene flow dynamics in Alpine plant species The focus of my doctoral thesis lies on the genetic diversity and local adaptation of plant species in the European Alps. It studied the consequences of climatic oscillations and drastic range changes in the Quaternary as well as adaptive processes in two Alpine plant species. In the first part, I have comprehensively studied whether and to what extent glacial history has affected the genetic population differentiation in the widespread species Geum reptans. The main hypothesis was that the phylogenetic structure of populations, caused by neutral genetic processes during isolation in glacial refugia and recolonisation of different Alpine regions, has led to population differentiation in phenotypic traits. Therefore, I combined a phylogenetic study (RAPD analysis) with a common garden experiment. The common garden experiment allowed the separation of genetic and environmental effects on the observed differentiation in phenotypic traits related to growth, reproduction and leaf morphology. Traits were measured after two seasons and the effect of phylogeographic region was analysed with linear mixed-effects models. I additionally hypothesised that at least part of the phenotypic differentiation is adaptive due to the recent environmental heterogeneity and that past selection acted on the traits. In order to proof this hypothesis, I performed correlation analyses with traits and climatic data of sites of population origin and a QST-FST analysis. In the second part of the thesis, I have studied the spatial genetic structure, gene flow dynamics and colonisation potential of the rare and monocarpic plant Campanula thyrsoides at small spatial scale in the Swiss Alps (Schynige Platte). For the molecular analysis I used microsatellites as markers and Bayesian structuring analysis as well as F-Statistics. The colonisation potential and distribution pattern of the species was investigated with a seed sowing experiment. A strong impact of glacial history on both genotypes as well as phenotypes in G. reptans was found, since phylogeographic structure was mirrored by regional phenotypic differentiation. Correlations of traits with climatic data of sites of population origin indicated that adaptation contributed to the observed phenotypic differentiation in growth and specific leaf area. Despite the small area, genetic differentiation in C. thyrsoides was considerably high, indicating restricted gene flow by seeds. Furthermore, the molecular analysis revealed that random genetic processes (i.e. drift and founder effects) are more important than gene flow. The seed sowing experiment confirmed the hypotheses that C. thyrsoides is strongly dispersal limited at the regional scale and microsite limited at the local scale. Thus, sowing of seeds to unoccupied but suitable habitats and a disturbance regime within these sites might be effective conservation strategies. Such a conservation management would be particularly worthwhile, if habitats of C. thyrsoides and other dispersal limited species continue to shrink as a consequence of changes in traditional land use or global warming.