Phenotypic differentiation in a common garden reflects the phylogeography of a widespread Alpine plant

Abstract

Summary1. Glacial history has affected the phylogeographic structure of numerous Alpine plant species, but its impact on phenotypic differentiation has been little studied. Therefore, we asked whether phenotypic differentiation in a common garden reflects the phylogeographic structure of the widespread Alpine plant Geum reptans L. 2. We combined a molecular investigation with a common garden experiment and investigated genets from 16 populations of G. reptans sampled from the European Alps. Using neutral molecular markers (RAPDs) and Bayesian cluster analysis, we analysed the species' genetic differentiation and phylogeographic structure. In the common garden, we measured the differentiation of phenotypic traits related to growth, reproduction and leaf morphology. 3. Molecular analysis partitioned the populations into three genetic groups, indicating pronounced phylogeographic structure. Regional molecular variation was correlated with regional phenotypic differentiation. 4. Quantitative trait differentiation (Q ST ) differed from neutral molecular differentiation (G ST ) in 10 of 11 traits, indicating that selection has contributed to phenotypic differentiation. Significant negative correlations between biomass and precipitation records for site of origin are a further indication of adaptation. 5. Synthesis. The current study compared regional molecular variation and phenotypic differentiation among populations of a widespread species in the context of extreme range changes during glaciations in the Alps. Because the common garden phenotypic differentiation of G. reptans reflects its phylogeographic structure, we conclude that glacial history affected both genotypes and phenotypes. The results suggest that the present-day phenotypic differentiation was caused by genetic drift and limited gene flow between populations in glacial refugia and during post-glacial recolonization, as well as by adaptation to current climatic conditions. Our findings are relevant for understanding the adaptive potential of Alpine plants and predicting potential range shifts in response to future climate change.

High intraspecific phenotypic variation, but little evidence for local adaptation in Geum reptans populations in the Central Swiss Alps

“…Supporting this interpretation, the selection analysis for mean leaf traits at different sites showed only little direct linear selection on these traits (Table 5), corroborating the fact that there was no divergent selection across the studied sites. Since only three populations from the Central Swiss Alps were studied here, it is important to note that adaptive genetic differentiation may in fact be found across larger geographic ranges, and such genetic differentiation may well be in line with this species' glacial history and postglacial recolonization (Frei et al 2012). …”

“…Intraspecific phenotypic variation resulting from genetic drift or natural selection (Volis et al 2015) is common in widely distributed species (Bradshaw 1984;Joshi et al 2001;Banta et al 2007) and has frequently been observed in alpine plant species (Pluess and Stöcklin 2004;Gimé-nez-Benavides et al 2007;Byars et al 2009;GonzaloTurpin and Hazard 2009;Stöcklin et al 2009;Frei et al 2012). Moreover, strong phenotypic plasticity is likewise common in alpine species, and has been shown to provide a potential advantage for the persistence and survival of alpine species in a heterogeneous environment (Stöcklin et al 2009;Frei et al 2014).…”

“…Furthermore, a glasshouse experiment revealed the great capacity of G. reptans to respond plastically to changes in environmental conditions, especially in its reproductive behavior (Pluess and Stöcklin 2005). Finally, a common garden experiment with 20 G. reptans populations spanning all biogeographic regions of the European Alps revealed that phenotypic differentiation reflected the glacial history of this species shaped by founder effects and past selection, but also suggested adaptation to current climate conditions (Frei et al 2012). However, to rigorously prove that adaptation to local conditions has occurred, reciprocal transplantation experiments across original field sites are necessary (Kawecki and Ebert 2004), which have so far never been performed with this species.…”

“…This species is an ideal system to study phenotypic variation and local adaptation, as it has been the subject of numerous prior investigations describing molecular and phenotypic variation, as well as gene flow among populations in the European Alps, and the relative importance of clonal vs. sexual reproduction Stöcklin 2004, 2005;Weppler et al 2006;Stöcklin et al 2009;Frei et al 2012). Findings from Weppler et al (2006) suggested that the role of sexual reproduction was not restricted to the maintenance of genetic variation or long-distance dispersal, but played an equally important role for population growth as reproduction via clonal offspring (Weppler et al 2006).…”

“…We investigated patterns of local adaptation in growth and reproductive traits by comparing the performance of sympatric and near-or far-allopatric site × population transplant combinations. We further measured leaf morphology traits known to be particularly plastic, yet not directly related to plant fitness (Frei et al 2012), and investigated plastic responses to environmental site effects. For all traits, we quantified the importance of genetic vs. environmental variation (i.e., phenotypic plasticity), and leaf traits were further used to investigate potential selection for mean trait values at each site.…”