J. F. Scheepens

Variability of protistan and bacterial communities in two Arctic fjords (Spitsbergen)

Krossfjorden and Kongsfjorden are Arctic fjords on the western side of Spitsbergen. These fjords share a common mouth to the open sea, and both are influenced by the input of sediment-rich glacial meltwater leading to decreased surface salinity, increased turbidity and decreased light penetration during summer. Earlier classical taxonomic studies had described the pelagic protistan composition of the Kongsfjorden during summer, revealing the dominance of flagellates of often unresolved taxonomic origin. Only little information existed on microbial eukaryote composition of the Krossfjorden as well as the bacterial composition of both fjords. The aim of the present study was to analyze and compare surface summertime protistan and bacterial communities in both fjords, using molecular approaches (16S and 18S rRNA DGGE, sequencing). Samples were collected three times a week from the central Kongsfjorden over a 1-month period. Additionally, 10 marine and 2 freshwater sites were sampled within a 1-week period in both Kongsfjorden and Krossfjorden. The central Kongsfjorden revealed a relatively stable protistan community over time with dinoflagellates, chlorophytes and small heterotrophs dominating. In contrast, the bacterial community varied over time and appeared to be correlated with the inflow of glacial meltwater. The Kongsfjorden and Krossfjorden were found to harbor distinctive bacterial and eukaryotic communities. We speculate that differences in glacial meltwater composition and fjord bathymetry affect the surface water properties and therefore the observed spatial variability in the community fingerprints.

Differentiation in morphology and flowering phenology between two Campanula thyrsoides L. subspecies

Subspecies are usually characterised by sets of morphological discontinuities. By means of common garden experiments, we investigated genetic differentiation in morphological and phenological traits in two geographically disjunct subspecies of Campanula thyrsoides L., i.e. subsp. thyrsoides (=C.* thyrsoides) occurring in the European Alps and Jura Mountains, and subsp. carniolica (=C.* carniolica) occurring in the Southeastern Alps and the Dinaric Arc. Nine out of 16 investigated traits were significantly different between C.* thyrsoides and C.* carniolica. For C.* carniolica inflorescence length was 1.4×, and above-ground biomass 2.7× higher, while flower density was significantly lower. Campanula* carniolica also showed delayed flowering and flower development from bottom to top as compared to C.* thyrsoides which flowered from top to bottom. The inflorescence growth was indeterminate and flowering took several weeks in C.* carniolica, whereas C.* thyrsoides showed determinate flowering, rapidly opening all flowers within a few days. This differentiation in flowering phenology is likely to be adaptive. The submediterranean climate favours indeterminate flowering in C.* carniolica, allowing ongoing growth of the inflorescence throughout the long summer until environmental conditions worsen, whereas determinate and early flowering in C.* thyrsoides is favourable in the short growing season in the high Alps where seed production must be secured before temperature drops. Glacial survival in refugia with different climates (alpine vs. submediterranean) may have caused this regional differentiation.

Simultaneous inbreeding modifies inbreeding depression in a plant–herbivore interaction

Because inbreeding is common in natural populations of plants and their herbivores, herbivore-induced selection on plants, and vice versa, may be significantly modified by inbreeding and inbreeding depression. In a feeding assay with inbred and outbred lines of both the perennial herb, Vincetoxicum hirundinaria, and its specialist herbivore, Abrostola asclepiadis, we discovered that plant inbreeding increased inbreeding depression in herbivore performance in some populations. The effect of inbreeding on plant resistance varied among plant and herbivore populations. The among-population variation is likely to be driven by variation in plant secondary compounds across populations. In addition, inbreeding depression in plant resistance was substantial when herbivores were outbred, but diminished when herbivores were inbred. These findings demonstrate that in plant-herbivore interactions expression of inbreeding depression can depend on the level of inbreeding of the interacting species. Furthermore, our results suggest that when herbivores are inbred, herbivore-induced selection against self-fertilisation in plants may diminish.

Distribution of bulbil- and seed-producing plants of Poa alpina (Poaceae) and their growth and reproduction in common gardens suggest adaptation to different elevations

UNLABELLED PREMISE OF THE STUDY The European Alps harbor a spatially heterogeneous environment. Plants can be adapted genetically to this heterogeneity but may also respond to it by phenotypic plasticity. We expected the important fodder grass Poa alpina to be adapted to elevation either genetically or plastically. • METHODS We investigated in three elevational common gardens whether growth and reproductive allocation of plants reproducing either by seeds or bulbils suggest adaptation to their elevation of origin and to what extent they can respond plastically to different elevations. Additionally, we analyzed genetic diversity using microsatellites and tested whether seeds are of sexual origin. • KEY RESULTS In the field, bulbil-producing plants occurred more often at higher elevations, whereas seed-producing plants occurred more often at lower elevations, but bulbil-producing plants were generally less vigorous in the common gardens. The response of plants to elevational transplantation was highly plastic, and vigor was always best at the highest location. The small genetic differences were not clinally related to elevation of origin, underlining the importance of phenotypic plasticity. Reproductive allocation was, however, independent of elevational treatments. Seed-producing plants had higher genetic diversity than the bulbil-producing plants even though we found that seed-producing plants were facultative apomicts mostly reproducing asexually. • CONCLUSIONS Bulbil-producing P. alpina, showing a fitness cost at lower elevations compared with seed-producing plants, seem better adapted to higher elevations. By means of its two reproductive modes and the capacity to adjust plastically, P. alpina is able to occupy a broad ecological niche across a large elevational range.

Glacial history affected phenotypic differentiation in the Alpine plant Campanula thyrsoides

Numerous widespread Alpine plant species show molecular differentiation among populations from distinct regions. This has been explained as the result of genetic drift during glacial survival in isolated refugia along the border of the European Alps. Since genetic drift may affect molecular markers and phenotypic traits alike, we asked whether phenotypic differentiation mirrors molecular patterns among Alpine plant populations from different regions. Phenotypic traits can be under selection, so we additionally investigated whether part of the phenotypic differentiation can be explained by past selection and/or current adaptation. Using the monocarpic Campanula thyrsoides as our study species, a common garden experiment with plants from 21 populations from four phylogeographic groups located in regions across the Alps and the Jura Mountains was performed to test for differentiation in morphological and phenological traits. Past selection was investigated by comparing phenotypic differentiation among and within regions with molecular differentiation among and within regions. The common garden results indicated regional differentiation among populations for all investigated phenotypic traits, particularly in phenology. Delayed flowering in plants from the South-eastern Alps suggested adaptation to long sub-mediterranean summers and contrasted with earlier flowering of plants experiencing shorter growing seasons in regions with higher elevation to the West. Comparisons between molecular and phenotypic differentiation revealed diversifying selection among regions in height and biomass, which is consistent with adaptation to environmental conditions in glacial refugia. Within regions, past selection acted against strong diversification for most phenotypic traits, causing restricted postglacial adaptation. Evidence consistent with post-glacial adaptation was also given by negative correlation coefficients between several phenotypic traits and elevation of the populations origin. In conclusion, our study suggests that, irrespective of adaptation of plants to their current environment, glacial history can have a strong and long-lasting influence on the phenotypic evolution of Alpine plants.

Glacial history and local adaptation explain differentiation in phenotypic traits in the Alpine grassland herb Campanula barbata

Background: Quaternary glaciations have affected the phylogeographic structure of many widespread plant species of the European Alps. Survival of plants in isolated refugia on the fringes of the Alps has been proposed as a main driver for molecular differentiation within species across the Alps, and could also be responsible for phenotypic differentiation. Aims: To establish if phenotypic differentiation is in accordance with phylogeographic structure and if population differentiation reflects adaptive processes. Methods: In a common garden we measured vegetative and reproductive traits of plants from 15 populations of two phylogeographic lineages of Campanula barbata from subalpine grasslands across the Alps. Results: The two phylogeographic lineages were differentiated in plant height and number of inflorescences, suggesting that glacial history affected phenotypic differentiation, either through neutral processes or adaptation. Furthermore, negative correlations of number of leaves, plant height, number of flowers and above-ground biomass with altitude of population origin indicated that part of the observed differentiation among populations was due to adaptation to current altitude-related conditions either during or after recolonisation. Conclusions: Our results suggest that phenotypic differentiation across the investigated regions may be due to glacial history-related processes as well as due to more recent processes of local adaptation.

Adaptation of flowering phenology and fitness-related traits across environmental gradients in the widespread Campanula rotundifolia

Abstract Plant populations need to adjust to climate warming through phenotypic plasticity or evolution of trait means. We performed a common-garden experiment with European populations of Campanula rotundifolia to investigate current adaptation in fitness-related traits and the potential for future adaptation. The common garden was situated in Switzerland and contained plants from 18 populations from four regions: Central Europe, The Netherlands, Scandinavia and the Swiss Alps. We assessed current adaptation with trait–environment correlations, and we compared molecular marker with trait differentiation to investigate past selection. How traits may change under future climate warming was investigated via selection analysis. Trait–trait correlations were performed to reveal genetic constraints. The majority of analysed phenotypic traits showed regional differentiation and all traits showed indications of past selection. Flowering duration decreased with latitude and elevation, suggesting adaptation to growing season length. The Central European populations performed best, indicating home-site advantage. Selection analysis showed positive selection on fitness-related traits whereas phenological traits showed less clear patterns. Trait–trait correlations were mostly neutral or favourable to selection. This study suggests that flowering phenology and other fitness-related traits of C. rotundifolia are adapted to the current climatic conditions and have the potential to evolve under climate change.

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

The Alpine landscape is characterized by high spatiotemporal heterogeneity in environmental variables, such as climate and soil characteristics. This may lead to divergent selection pressures across plant populations and to local adaptation. Geum reptans, a widespread high-alpine clonal herb, has been the subject of several studies investigating phenotypic variation in populations across the Swiss Alps, yet so far, there is only little knowledge about local adaptation in this species from reciprocal transplantations across original field sites. Here, we reciprocally transplanted three populations of Geum reptans in the Central Swiss Alps, growing at close or far geographical distance from each other, and compared growth- and reproduction-related traits to investigate patterns of local adaptation. We further measured leaf morphological traits to assess potential selection at field sites, and quantified the relative importance of genetic vs. environmental variation (i.e., phenotypic plasticity) for all traits. Additionally, among and within population genetic differentiation was analyzed using microsatellite markers. Molecular diversity was high within populations, and molecular differentiation increased with geographic distance among populations, suggesting that gene flow is maintained at close range, but decreased with distance. Although extensive phenotypic variation was found across site × population transplant combinations, our study revealed little evidence for local adaptation in G. reptans populations. Plant traits also showed strong plasticity, as revealed by pronounced site effects, yet no direct linear selection was detected on leaf trait values within field sites. We suggest that the glacier forelands studied here, which are representative of the habitat of large G. reptans populations, are too similar in environmental conditions to lead to among population intraspecific differentiation in line with local adaptation. As G. reptans showed a great capacity to respond plastically to environmental conditions, we cautiously advocate that the evolution of phenotypic plasticity might have prevailed over genetic differentiation for the adaptation to the relatively narrow niche of this species.

Spatiotemporal variation in local adaptation of a specialist insect herbivore to its long-lived host plant.

Local adaptation of interacting species to one another indicates geographically variable reciprocal selection. This process of adaptation is central in the organization and maintenance of genetic variation across populations. Given that the strength of selection and responses to it often vary in time and space, the strength of local adaptation should in theory vary between generations and among populations. However, such spatiotemporal variation has rarely been explicitly demonstrated in nature and local adaptation is commonly considered to be relatively static. We report persistent local adaptation of the short‐lived herbivore Abrostola asclepiadis to its long‐lived host plant Vincetoxicum hirundinaria over three successive generations in two studied populations and considerable temporal variation in local adaptation in six populations supporting the geographic mosaic theory. The observed variation in local adaptation among populations was best explained by geographic distance and population isolation, suggesting that gene flow reduces local adaptation. Changes in herbivore population size did not conclusively explain temporal variation in local adaptation. Our results also imply that short‐term studies are likely to capture only a part of the existing variation in local adaptation.

Relationship between phenotypic differentiation and glacial history in a widespread Alpine grassland herb

In the European Alps, alpine species were able to survive periods of glaciation by retreating to lower-lying refugia surrounding the Alps. This temporary separation of populations in refugia has often led to genetic differentiation and the appearance of phylogeographic lineages, which are still detectable after postglacial recolonisation. Recently, evidence has been accumulating that glacial history also affected differentiation of phenotypic traits, but it is yet unknown to what extent postglacial connectivity among populations influenced the signature left behind by the history of glaciation. In this study, we demonstrate differentiation in phenotypic traits among three phylogeographic lineages of the widespread subalpine grassland herb, Geum montanum, using a common garden approach. We observed regional differentiation in 5 out of 16 traits, which was a small portion compared with a closely related species that has been previously studied, Geum reptans. This may possibly be due to species-specific differences in their respective distributions: G. montanum has well-connected populations whereas G. reptans occurs more often in isolated high-alpine environments. Results of a clipping treatment, designed to address responses in phenotypic traits to stress, showed regional differentiation in the response in number of flowers produced. This is potentially due to adaptations shaped by unknown histories of herbivory during glacial survival. We suggest that glacial history may leave its mark on the current phenotypic variability even of Alpine plants that are relatively common with well-connected populations.