Plant speciation in the face of recurrent climate changes in the Alps

The main, continuous mountain range of the European Alpine System (i.e., the Alps) hosts a diversified pool of species whose evolution has long been investigated. The legacy of past climate changes on the distribution of high-elevation plants as well as taxa differentially adapted to the mosaic of edaphic conditions (i.e., surmised ecotypes on calcareous, siliceous, serpentine bedrocks) and the origin of new species are here discussed based on available evidence from endemic taxa across the Alps. The integration of main spatial and ecological patterns within and among species supports speciation driven by spatial isolation in main glacial refugia where plant populations survived during cold phases and hindered by intense gene flow along main expansion pathways during warm phases. Despite patterns of genetic differentiation matching environmental heterogeneity, processes underlying the dynamics of distribution ranges likely promoted recurrent homogenization of incipient divergence and generally hindered the completion of speciation (except for cases of hybrid speciation). Even intense selective pressures on toxic bedrocks such as serpentine seemingly fail to support the completion of speciation. Accordingly, typical scenarios of ecological speciation whereby local adaptation to environmental heterogeneity initiates and supports long-term reduction of gene flow may rarely be at the origin of stable species in the Alps. Although consistent with neutral processes whereby spatial isolation driven by past climate changes promoted reproductive isolation and yielded limited diversification, mechanisms at the origin of new species across heterogeneous landscapes of the Alps remain insufficiently known. Necessary advances to reliably understand the evolution of biodiversity in the Alps and identify possible museums or cradles of variation in face of climate changes are discussed

Postglacial recolonisation of plants in the western Alps of Switzerland

Parisod C. 2008. Postglacial recolonisation of plants in the western Alps of Switzerland. Bot. Helv. 118: 1 - 12. During the Quaternary glaciations, alpine plants could only persist in scattered icefree areas located either within the Alps or at their periphery. From there, species recolonised the Alps after the retreat of glaciers, and efforts have been made to reconstruct the main migration pathways using either floristic information (i.e. patterns of species distribution) or studies of infraspecific genetic variation (i.e. distribution patterns of genotypes or lineages). This review article compiles floristic and molecular information about the recolonisation of the western Swiss Alps. Three main pathways of recolonisation have been suggested in the literature: the Rhodanian pathway (from south-western refugia, along the Rhone valley), the transalpine southern pathway (from southern refugia, crossing the line of main summits through high-altitude passes), and the transalpine eastern pathway (from eastern refugia, along the Rhine valley and across the northern Alps). Floristic data mainly support the Rhodanian pathway, as many western Alpine species occur along this route, as well as the transalpine southern pathway, as some southern species occur in the vicinity of the relevant passes. In contrast, few species show distribution patterns consistent with the transalpine eastern pathway. Recent molecular studies have supported the floristic patterns. In particular, distinct genetic lineages of the widespread alpine species Biscutella laevigata were distributed along the Rhodanian pathway and transalpine southern pathway, and genetic diversity was especially high in the central area, where these recolonisation pathways met. Knowledge about past migration routes of plants is essential to understand the response of species to climate change and the present patterns of biodiversity within the Alp

Divergent selection in trailing- versus leading-edge populations of Biscutella laevigata

Background and Aims Knowledge on how climate-induced range shifts might affect natural selection is crucial to understand the evolution of species ranges. Methods Using historical demographic perspectives gathered from regional-scale phylogeography on the alpine herb Biscutella laevigata, indirect inferences on gene flow and signature of selection based on AFLP genotyping were compared between local populations persisting at the trailing edge and expanding at the leading edge. Key Results Spatial autocorrelation revealed that gene flow was two times more restricted at the trailing edge and genome scans indicated divergent selection in this persisting population. In contrast, no pattern of selection emerged in the expanding population at the leading edge. Conclusions Historical effects may determine different architecture of genetic variation and selective patterns within local populations, what is arguably important to understand evolutionary processes acting across the species range

Genetic Variability and Founder Effect in the Pitcher Plant Sarracenia purpurea (Sarraceniaceae) in Populations Introduced into Switzerland: from Inbreeding to Invasion

• Background and Aims The long-lived and mainly outcrossing species Sarracenia purpurea has been introduced into Switzerland and become invasive. This creates the opportunity to study reactions to founder effect and how a species can circumvent deleterious effects of bottlenecks such as reduced genetic diversity, inbreeding and extinction through mutational meltdown, to emerge as a highly invasive plant. • Methods A population genetic survey by random amplified polymorphism DNA markers (RAPD) together with historical insights and a field pollination experiment were carried out. • Key Results At the regional scale, S. purpurea shows low structure (θst = 0·072) due to a recent founder event and important subsequent growth. Nevertheless, multivariate statistical analyses reveal that, because of a bottleneck that shifted allele frequencies, most of the variability is independent among populations. In one population (Tenasses) the species has become invasive and genetic analysis reveals restricted gene flow and family structure (θst = 0·287). Although inbreeding appears to be high (Fis > 0·410 from a Bayesian estimation), a field pollination experiment failed to detect significant inbreeding depression upon F1 seed number and seed weight fitness-traits. Furthermore, crosses between unrelated individuals produced F1 seeds with significantly reduced fitness, thus showing local outbreeding depression. • Conclusions The results suggest that, under restricted gene flow among families, the species may not only have rapidly purged deleterious alleles, but also have undergone some form of selection for inbreeding due to co-adaptation between loc

Marie Brockmann-Jerosch and her influence on Alpine phylogeography

At the beginning of the twentieth century, Marie Brockmann-Jerosch wrote, partly in collaboration with her husband Heinrich Brockmann-Jerosch, three influential overview articles on the origin and history of the Swiss alpine flora. Of special interest to her were the types and locations of Pleistocene glacial refugia of alpine plants. She summarised that there had been glacial refugia in the southern and northern peripheral European Alps and also supported glacial survival of high-alpine specialist plants in central Alpine nunatak regions within glaciated areas of the Alps. In contrast, Marie Brockmann-Jerosch dismissed the occurrence of glacial relicts in the lowlands and foothills north of the Alps: she rather saw the conspicuous stations of alpine plants in the lowlands as the result of post-glacial long-distance dispersal of seed out of the Alps. In this article, we first give a brief description of Marie Brockmann-Jerosch's life and then show that modern phylogeographic research has largely proven her views of the glacial history of the alpine flora and that her writings are still intellectually stimulating and worthwhile readin

Climate Change and Alpine Screes: No Future for Glacial Relict Papaver occidentale (Papaveraceae) in Western Prealps

Glacial relicts, especially those with very narrow habitat requirements, are particularly affected by global warming. We considered Papaver occidentale, a glacial relict endemic to the Western Prealps, belonging to the alpine poppy complex (P. alpinum aggr.), as a model taxon to study the actual status and potential future distribution of species restricted to particular microrefugia. For this study, all known localities were visited, each population was georeferenced and the number of individuals was estimated. Species Distribution Modelling (SDM) was used to evaluate the present and future potential distribution range and habitat suitability, taking into account the specificity of its habitat (calcareous screes). According to our study, there are globally 19 natural populations of P. occidentale, and a total of about 30,000 individuals. The taxon is a highly specialized alpine plant growing in the majority of natural sites between 1900 and 2100 m a.s.l. on north-facing screes. Predictions for the end of the 21st century indicate that a suitable area will significantly decrease (0–30% remaining). Under the most severe climatic scenarios (RCP 8.5), the species risks complete extinction. The long-term in situ conservation of P. occidentale, and all other taxa of the P. alpinum complex, is unlikely to be achieved without slowing global climate change. More generally, our fine-scale study shows that local environmental buffering of large-scale climate change in high-mountain flora may be very limited in specialised taxa of patchy environments such as screes

Phylogenetics and Biogeography of Lilium ledebourii from the Hyrcanian Forest

ilium ledebourii (Baker) Boiss is one of the most endangered lilies, restricted to only a few small and fragmented areas in the Hyrcanian forest. This study aimed at evaluating the taxonomy of this unique Iranian lily and reconstructing divergence time from other species of the genus Lilium to address the role of this region in its diversification. Phylogenetic trees based on nuclear ITS and chloroplastic matK strongly supported the monophyly of the genus Lilium and division into subclades hardly matching prior morphological classifications. Biogeographic analyses using S-DIVA revealed East Asia as the ancestral range from where Lilium presented a multidirectional expansion towards North America, West-Central Asia, North Asia, and Europe. Diverging from ancestral Lilium during the beginning of Eocene (50 Ma; 95% HDP: 68.8–36.8). Specific members of Lilium colonized Iran (Western Asia) separated from the Clade IV (West-Central Asia and Europe lineage), and then yielded the Iranian L.ledebourri. Accordingly, the north of Iran appears to have promoted both long-term persistence and migration of Lily species from Asia to the Europe