Christoph Reisch

Genetic variation of Eryngium campestre L. (Apiaceae) in Central Europe.

In Germany, Eryngium campestre is restricted to dry habitats along the rivers Rhine and Elbe and to a few areas in Central Germany. This distribution pattern is usually regarded as a typical pattern of postglacial immigration. In the present study, we investigated whether these two geographically distinct distribution areas are genetically differentiated and whether conclusions can be drawn regarding colonization history. To analyse the phylogeographic structure of E. campestre in Central Europe, 278 individuals from 29 populations within Germany and from further reference populations within Europe were analysed. We applied amplified fragment length polymorphisms to examine their genetic relatedness. Our analyses revealed three groups: a Mediterranean group additionally including two Rhine populations; a Rhine–Main group which further includes the westernmost population from the central German dry area; and one group which includes all eastern populations. Our results show that the two geographically distinct areas are genetically differentiated. As genetic diversity within the Elbe populations is very low, we conclude that this area, which was strongly affected through the late glacial maximum, was colonized relatively recently. High genetic diversity in the Rhine populations indicates a contact zone where lineages of different origin met. This would imply that todays patterns of genetic variation were caused through glacial range contractions and expansions. The present study is one of the first studies that deal with the postglacial distribution pattern of a dry grassland plant species in Central Europe and the results suggest that a survival of E. campestre at least during the Dryas cold stage might be possible.

The impact of study design and life history traits on genetic variation of plants determined with AFLPs

In this study, we analysed the impact of study design and life history traits on genetic variation of plants determined with amplified fragment length polymorphisms (AFLPs), a technique widely applied in all fields of molecular plant ecology. For the proper interpretation and comparison of genetic variation based upon AFLPs, a meta-analysis based upon a large number of studies of the relationship between study design and plant life history traits on the one hand and of AFLP variation on the other hand is needed but is lacking. To bridge this gap, we extracted data on study design and genetic variation from 115 AFLP studies comprising a total of 152 species. Subsequently, we ascribed the life history traits taxonomic status, life span, frequency, mating system and pollination vector to each of the species. Then, we used linear models to analyse the impact of study design and life history traits on genetic variation. In our data set genetic variation within and among populations depended neither on the number of analysed populations nor the number of analysed individuals per population. However, maximum geographic distance between populations strongly affected genetic variation. Variation within populations decreased while variation among populations increased with maximum geographic distance. Concerning the impact of life history traits, both genetic variation within and among populations depended with increasing strength on the life span, the frequency and the mating system of the species. Following the results of this study, the number of analysed populations or individuals per population is not necessarily a problem when comparing results of different studies, at least when not very low sample sizes are used. However, corresponding study ranges would be highly recommendable, since the maximum geographic distance between populations strongly affects genetic variation.

Intraspecific variation, land use and habitat quality – a phenologic and morphometric analysis of Sesleria albicans (Poaceae)

Summary In central Europe populations of Sesleria albicans (Poaceae) are located in habitats which strongly differ from each other with regard to habitat quality (light, water, nutrients) and land-use (grazing, mowing). Variation among these populations as a result of selection and adaptation to different environments can be supposed. In a common garden experiment we investigated 16 populations of Sesleria albicans from natural open habitats (rock faces, rocky ridges) natural closed habitats (beech forests) and anthropogenic open habitats (grazed calcareous grasslands, mown fens) for phenologic and morphometric differentiation. Our investigation revealed that plants from calcareous grasslands flowered and fruited much earlier than plants from fens. Four of 13 morphometric characters showed significant differences among populations. Plants from rock faces had longer leaves and larger tussocks than plants from grazed calcareous grasslands and mown fens. Plants from rock faces showed strongly stretched and plants from fens strongly compressed flowering culms. Plants from fens had the highest number of tillers per tussock. The intraspecific variation of Sesleria albicans is not due to phenotypic plasticity, since it persisted in a common garden experiment, but probably the result of different habitat quality and land use and the concomitant selection. Small size and strong vegetative propagation of plants from calcareous grasslands and fens are probably caused by grazing or mowing and show the powerful influence of land use practices on the intraspecific variation of Sesleria albicans .

Disturbance by mowing affects clonal diversity: the genetic structure of Ranunculus ficaria (Ranunculuaceae) in meadows and forests

To study the impact of disturbance by mowing on clonal variation, we compared the genetic structure of Ranunculus ficaria (Ranunculaceae) in meadows and forests located in southeast Germany. We applied random amplified polymorphic DNA (RAPD) analysis to investigate the clonal and genetic diversity and analysed a total of 117 samples from three study plots in each habitat type. Polymerase chain reaction with six primers resulted in 57 fragments. Clonal diversity differed clearly between the two analysed habitat types and was significantly higher in the study plots from meadows than in those from forests. The mean percentage of distinguishable genotypes (PD) was 0.80 in meadow plots and 0.36 in forest plots, and the detected genets were smaller in meadow plots than in forest plots. Mean genetic diversity measured as percentage of polymorphic bands, Shannon’s information index and Nei’s gene diversity was also higher in meadows (44.4, 0.22 and 0.14) than in forests (25.1, 0.09 and 0.05). The higher level of clonal diversity in meadow plots is most likely due to the effects of disturbance by mowing, which increases the dispersal of bulbils and promotes the establishment of new plants in meadows compared to forests.

Vital survivors: low genetic variation but high germination in glacial relict populations of the typical rock plant Draba aizoides

Glacial relict populations are isolated remnants of arctic-alpine species resulting from shifts of the distribution range during glaciations. Recently, the conservation value of relict populations has been emphasized, since they are adapted to stressful ecological conditions, which may be important for future distribution range shifts due to climate change. However, glacial relict populations have strongly been affected by historical fragmentation processes. Limited genetic variation and reduced reproduction can, therefore, be postulated for glacial relict populations. In our study we tested these assumptions. We investigated central European populations of the typical rock plant Draba aizoides from the Alps (considered as a core distribution area) and from the Swabian Alb, the Southern and Northern Franconian Jura (where its populations are considered glacial relict populations). We analysed genetic variation using molecular markers AFLPs and studied the reproduction of the populations in germination experiments. Glacial relict populations were genetically less variable and strongly differentiated, but they exhibited higher germination than populations from the Alps. From our results it can be concluded that glacial relict populations may have limited genetic variation, but they do not necessarily exhibit a limited reproductive capacity. Glacial relict populations are, therefore, vital survivors of the Pleistocene, which deserve full conservation attention, especially against the background of future climate change.

Long-term study of an alpine grassland: local constancy in times of global change

The impact of climate change, especially on alpine vegetation is well documented. Here, we present the results of a long-term study on the vegetation composition of an alpine grassland (Caricetum curvulae) located in the central Alps, where we performed vegetation surveys since 1980. Our study comprised 99 non-permanent plots that were randomly distributed in the studied grassland and contained 59 species in total. We estimated species cover in each plot and conducted a detrended correspondence analysis to investigate changes in vegetation composition since 1980. We also calculated species richness, evenness, as well as Shannon diversity for each plot and computed Jaccard similarity between the plots of the same year as well as between the plots of 1980 and all subsequent years. Linear regression analyses were carried out to test these parameters for significant changes between 1980 and 2012. In the correspondence analysis, plots from all years were intermixed and the sampling year as a factor was not correlated with the axes. Species richness, evenness and Shannon diversity of the study plots, as well as the Jaccard similarity between the plots of the same year and between plots of 1980 and all subsequent years did not change significantly since 1980. The cover of individual species within plots changed significantly for only six out of the 59 identified species. Polygonum vivparum and Oreochloa disticha decreased, whereas Vaccinium vitis-idea, Luzula alpina, Avenochloa versicolor, and Agrostis rupestris increased significantly since 1980. The results of our study revealed almost no changes in vegetation composition and only very small changes in species cover, although temperature continuously rose since 1980. This local constancy in times of global change can most likely be attributed to the extreme longevity of many alpine grassland species and, therefore, to the persistence of alpine grasslands.

Species distribution modeling and molecular markers suggest longitudinal range shifts and cryptic northern refugia of the typical calcareous grassland species Hippocrepis comosa (horseshoe vetch)

Abstract Calcareous grasslands belong to the most diverse, endangered habitats in Europe, but there is still insufficient information about the origin of the plant species related to these grasslands. In order to illuminate this question, we chose for our study the representative grassland species Hippocrepis comosa (Horseshoe vetch). Based on species distribution modeling and molecular markers, we identified the glacial refugia and the postglacial migration routes of the species to Central Europe. We clearly demonstrate that H. comosa followed a latitudinal and due to its oceanity also a longitudinal gradient during the last glacial maximum (LGM), restricting the species to southern refugia situated on the Peninsulas of Iberia, the Balkans, and Italy during the last glaciation. However, we also found evidence for cryptic northern refugia in the UK, the Alps, and Central Germany. Both species distribution modeling and molecular markers underline that refugia of temperate, oceanic species such as H. comosa must not be exclusively located in southern but also in western of parts of Europe. The analysis showed a distinct separation of the southern refugia into a western cluster embracing Iberia and an eastern group including the Balkans and Italy, which determined the postglacial recolonization of Central Europe. At the end of the LGM, H. comosa seems to have expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, and Germany.

Spatial Genetic Structure of the Sedge Carex Nigra Reflects Hydrological Conditions in an Alpine Fen

Abstract Fine-scale genetic structure of plant populations depends on several ecological processes. In this study, we analyzed the impact of hydrological heterogeneity on the spatial genetic structure of the wind-pollinated black sedge Carex nigra in an alpine fen. We performed amplified fragment length polymorphisms (AFLPs) with 111 samples collected along a grid covering the whole area of the fen and studied fine-scale genetic structure using spatial autocorrelation and Bayesian cluster analyses. We observed a significant spatial genetic structure indicating isolation-by-distance, which can be ascribed to restricted seed dispersal. Bayesian cluster analysis revealed four groups of genetically related and patchy distributed samples within the fen. Two of these groups were distributed in the deeper and moister regions of the fen, while the two other groups were spatially restricted to the higher and drier regions of the fen. We think that the observed pattern of spatial genetic variation reflects hydrological heterogeneity within the fen and conclude that the four groups represent cohorts of individuals originating from different recruitment events in different parts of the fen. Genetic variation was much lower in the groups from the drier regions of the fen. Since Carex species require moist conditions for germination and establishment, the low level of genetic variation can most likely be ascribed to restricted seedling recruitment in the drier regions of the fen. Habitat heterogeneity affects, therefore, both spatial genetic structure and levels of genetic variation. This study clearly demonstrates that integrating fine-scale genetic analyses with complementary biological data can markedly improve the identification of processes that shape fine-scale genetic structure within plant populations.

Genetic diversity of calcareous grassland plant species depends on historical landscape configuration

BackgroundHabitat fragmentation is considered to be a main reason for decreasing genetic diversity of plant species. However, the results of many fragmentation studies are inconsistent. This may be due to the influence of habitat conditions, having an indirect effect on genetic variation via reproduction. Consequently we took a comparative approach to analyse the impact of habitat fragmentation and habitat conditions on the genetic diversity of calcareous grassland species in this study. We selected five typical grassland species (Primula veris, Dianthus carthusianorum, Medicago falcata, Polygala comosa and Salvia pratensis) occurring in 18 fragments of calcareous grasslands in south eastern Germany. We sampled 1286 individuals in 87 populations and analysed genetic diversity using amplified fragment length polymorphisms. Additionally, we collected data concerning habitat fragmentation (historical and present landscape structure) and habitat conditions (vegetation structure, soil conditions) of the selected study sites. The whole data set was analysed using Bayesian multiple regressions.ResultsOur investigation indicated a habitat loss of nearly 80% and increasing isolation between grasslands since 1830. Bayesian analysis revealed a significant impact of the historical landscape structure, whereas habitat conditions played no important role for the present-day genetic variation of the studied plant species.ConclusionsOur study indicates that the historical landscape structure may be more important for genetic diversity than present habitat conditions. Populations persisting in abandoned grassland fragments may contribute significantly to the species’ variability even under deteriorating habitat conditions. Therefore, these populations should be included in approaches to preserve the genetic variation of calcareous grassland species.

Glacial refugia and postglacial expansion of the alpine–prealpine plant species Polygala chamaebuxus

Abstract The shrubby milkwort (Polygala chamaebuxus L.) is widely distributed in the Alps, but occurs also in the lower mountain ranges of Central Europe such as the Franconian Jura or the Bohemian uplands. Populations in these regions may either originate from glacial survival or from postglacial recolonization. In this study, we analyzed 30 populations of P. chamaebuxus from the whole distribution range using AFLP (Amplified Fragment Length Polymorphism) analysis to identify glacial refugia and to illuminate the origin of P. chamaebuxus in the lower mountain ranges of Central Europe. Genetic variation and the number of rare fragments within populations were highest in populations from the central part of the distribution range, especially in the Southern Alps (from the Tessin Alps and the Prealps of Lugano to the Triglav Massiv) and in the middle part of the northern Alps. These regions may have served, in accordance with previous studies, as long‐term refugia for the glacial survival of the species. The geographic pattern of genetic variation, as revealed by analysis of molecular variance, Bayesian cluster analysis and a PopGraph genetic network was, however, only weak. Instead of postglacial recolonization from only few long‐term refugia, which would have resulted in deeper genetic splits within the data set, broad waves of postglacial expansion from several short‐term isolated populations in the center to the actual periphery of the distribution range seem to be the scenario explaining the observed pattern of genetic variation most likely. The populations from the lower mountain ranges in Central Europe were more closely related to the populations from the southwestern and northern than from the nearby eastern Alps. Although glacial survival in the Bohemian uplands cannot fully be excluded, P. chamaebuxus seems to have immigrated postglacially from the southwestern or central‐northern parts of the Alps into these regions during the expansion of the pine forests in the early Holocene.