Johannes Fredericus (Niek) Scheepens

Abstract: Background: Quaternary glaciations 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 is proposed as a main driver for molecular differentiation within species across the Alps, and could also be responsible for phenotypic differentiation. Aims: To establish whether phenotypic differentiation is in accordance with phylogeographic structure and whether population differentiation reflects adaptive processes. Methods: In the common garden we measured vegetative and reproductive traits of plants from 15 populations of two phylogeographic lineages of <i>Campanula barbata</i> 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.

Abstract: Knowledge on the limitation of plant species’ distributions is important for preserving alpine biodiversity, particularly when the loss of alpine habitats because of global warming or land use changes is faster than colonization of new habitats. We investigated the potential of the rare alpine plant <i>Campanula thyrsoides</i> L. to colonize grassland sites of different suitability on a small mountain plateau in the Swiss Alps. A total of 15 experimental sites were selected according to their differences in habitat suitability for adult <i>C. thyrsoides</i>, which was measured by the Beals index. At each site we applied a disturbance treatment, added seeds at different densities and monitored the survival of seedlings over two consecutive years. The number of surviving seedlings was not positively related to habitat suitability for adult <i>C. thyrsoides</i>. Furthermore, <i>C. thyrsoides</i> appears to be strongly dispersal limited at the regional scale because seed addition to unoccupied habitats resulted in successful germination and survival of seedlings. Since an increase of seed density in already occupied sites did not affect the number of seedlings, we suggest that <i>C. thyrsoides</i> is microsite limited at the local scale. Microsite limitation is supported by the result that seedling survival of the species was enhanced in vegetation gaps created by disturbance. We conclude that <i>C. thyrsoides</i> may become endangered in the future if environmental changes cause local extinction of populations. An appropriate management, such as a disturbance regime for enhancing recruitment in existing populations, may ensure the long-term survival of this rare alpine plant species.

Abstract: 1. 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 <i>Geum reptans</i> L. 2. We combined a molecular investigation with a common garden experiment and investigated genets from 16 populations of <i>G. reptans</i> 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 (<i>Q</i>_ST) differed from neutral molecular differentiation (<i>G</i>_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 <i>G. reptans</i> 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.

Abstract: Changes in climate and traditional land use have contributed to a loss and fragmentation of suitable habitats for many alpine plant species. Despite the importance of these changes, our knowledge of the consequences for gene flow and genetic diversity is still poor, especially in rare taxa and at fine spatial scales. Here, we investigated the genetic diversity in a rare alpine plant on a small and highly structured mountain in the Swiss Alps. Using microsatellite markers and Bayesian cluster analyses, we investigated genetic diversity within and among 24 populations of Campanula thyrsoides L. We also tested whether landscape structure has affected genetic structure by correlating genetic diversity with landscape and population features, which were assessed in a four-year monitoring period. The recorded genetic diversity (He = 0.714) and genetic differentiation (G’ST = 0.32) at distances of 1–10 km were remarkably high. Clustering analyses revealed a split of populations into two genetically different spatial groups, but between-population genetic distances were neither correlated to geographic distance, elevation nor slope. The high differentiation and genetic bottlenecks may indicate strong founder effects, although the number of alleles was not decreased in bottlenecked populations. We conclude that stochastic colonisation by seeds is most important for shaping the genetic structure of C. thyrsoides on this small mountain. The high genetic diversity even in small populations may indicate that occasional gene flow is strong enough to overcome negative effects of bottlenecks. Nevertheless, further fragmentation and isolation of habitats may threaten this rare plant in the future.

Abstract:

Abstract: Quaternary climate change had profound impacts on the geographical distribution and genetic structure of plant species which is hypothesized to have triggered allopatric speciation due to spatial isolation. However, evidence is scarce despite recent advances that indicate glacial history and substrate requirements as main drivers of spatial genetic structures. Here we built upon these studies to test the role of glaciations on the morphological and ecological differentiation within the calcicolous <i>Campanula thyrsoides</i> across its European Alpine distribution range. We collected samples from 51 populations (1173 plants), used five microsatellite markers, estimated diversity (N_a, H_E) and differentiation (D_est, G_{ST_est}, F_ST) and applied Bayesian clustering analysis and tessellation methods. We found support for four genetically distinct groups of populations, arranged from West to East: i) France and Western Switzerland, ii) Central and most of Eastern Switzerland, iii) parts of Eastern Switzerland and Central Austria, and iv) Southeastern Austria, Slovenia and Northeastern Italy. Among-subspecies variance was 8.4% and each subspecies was highly differentiated (<i>C.*thyrsoides</i>: D_est = 0.47; <i>C.*carniolica</i>: D_est = 0.58). Geographic structuring of within-population diversity was not related to refugia outside of previously-glaciated terrain but to subspecies: the more thermophilic <i>C.*carniolica</i> showed significantly lower levels of within-population diversity and higher numbers of private alleles. The location of the genetic break lines between these four groups of populations correspond to well-known biogeographic barriers. However, the phylogeographic pattern has elements formerly found in both calcicolous and silicicolous species and thus questions the generality of substrate-related patterns. Within <i>C.*thyrsoides</i>, population admixture upon secondary contact may have led to high genetic diversity across the distribution range. Given the geographic and genetic differences of the subspecies we conclude that differentiation between <i>C.*thyrsoides</i> and <i>C.*carniolica</i> represents a case of glaciation-driven allopatric subspeciation reinforced by missing secondary contact due to incomplete post-glacial recolonization of potential habitats.

Abstract: Subspecies are usually characterized 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 <i>Campanula thyrsoides</i> L., i.e. subsp. <i>thyrsoides</i> (= <i>C.* thyrsoides</i>) occurring in the European Alps and Jura Mountains, and subsp. <i>carniolica</i> (= <i>C.* carniolica</i>) occurring in the Southeastern Alps and the Dinaric Arc. Nine out of 16 investigated traits were significantly different between <i>C.* thyrsoides</i> and <i>C.* carniolica</i>. For <i>C.* carniolica</i> inflorescence length was 1.4×, and above-ground biomass 2.7× higher, while flower density was significantly lower. <i>Campanula* carniolica</i> also showed delayed flowering and flower development from bottom to top compared to <i>C.* thyrsoides</i> which flowered from top to bottom. The inflorescence growth was indeterminate and flowering took several weeks in <i>C.* carniolica</i>, whereas <i>C.* thyrsoides</i> 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 <i>C.* carniolica</i>, allowing ongoing growth of the inflorescence throughout the long summer until environmental conditions worsen, whereas determinate and early flowering in <i>C.* thyrsoides</i> 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.

Abstract: Specific leaf area (SLA) is an important plant functional trait as it is an indicator of ecophysiological characteristics like relative growth rate, stress tolerance and leaf longevity. Substantial intraspecific variation in SLA is common and usually correlates with environmental conditions. For instance, SLA decreases with increasing altitude, which is understood as adjustment to temperature. It is generally assumed that intraspecific variation is mostly the result of environmentally induced phenotypic plasticity, but genetic effects may also be present, due to local adaptation or genetic drift. In this study, genotypic and environmental effects on SLA were experimentally separated for the widespread Alpine bell flower Campanula thyrsoides by transplanting plants to three common gardens at contrasting altitudes (600m, 1235m and 1850m a.s.l.). Seeds were sampled from 18 populations in four phylogeographic regions within the European Alps. A strong plastic response was observed: SLA decreased with increasing altitude of the common gardens (22.0% of variation). The phylogeographic regions were differentiated in SLA in the common gardens (10.1% of variation), indicating that SLA is at least partly genetically determined. Plants from the six easternmost populations experienced a submediterranean climate and showed decreased SLA values in the three common gardens compared to populations to the west, which may be explained as adaptation to drought. Within these submediterranean populations, SLA decreased with altitude of origin in two out of three common gardens. Concluding, SLA shows strong phenotypic plasticity as well as substantial genetic effects, the latter probably being the result of adaptation to local conditions rather than genetic drift.

Abstract: QST vs. FST comparisons can reveal diversifying or unifying selection pressures among populations for specific traits. In this study we performed QST-FST analyses on eleven populations of Scabiosa columbaria from the Swiss Jura to reveal genetic differentiation in two quantitative traits (above-ground biomass and relative growth rate of leaf lengths) and in neutral molecular markers. Above-ground biomass of plants under competition has been shown to correlate with their competitive ability, which is an important fitness-related trait. We hypothesized that strong unifying selection acts on above-ground biomass, since underperformance would result in decreased fitness and overperformance is unlikely due to trade-offs with other plant functions. Overall GST (an FST analogue) was 0.12. Analysis of variance revealed that above-ground biomass and relative growth rate did not differ among populations, but both traits differed among seed families and were heritable (h2=0.31 and h2=0.35 respectively). QST was close to zero for above-ground biomass and zero for relative growth rate of leaf lengths, and thus QST was much lower than GST, indicating unifying selection on these traits. This conclusion is restricted by the limits of the used methodology. QST<FST cannot always be considered as a proof for unifying selection, because in complex traits the assumption of purely additive effects of underlying genes may be violated. However, given the large differences between QST and GST, together with substantial heritabilities of the traits under study, we conclude that our findings are not in contradiction with the hypothesis of unifying selection.

Abstract: 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.

Abstract: Elytrigia atherica is a tall clonal grass species typical of higher salt marshes, but is gradually invading to the lower marshes. At young successional stages of a salt marsh, E. atherica is found sparsely dispersed in small groups of ramets. These patches increase in size and ramet density over time, eventually forming extensive swards as succession proceeds. This study investigates the change in the clonal diversity of E. atherica stands during colonization as a result of its reproductive strategy. Clonal diversities of differently sized patches of E. atherica were investigated on two lower salt-marsh sites of different age, 25 years and 35†years, respectively. Microsatellite fingerprint patterns were used to determine genet identities and to estimate relatedness and genetic differentiation between the sites, between patches within sites and within patches. The majority of the patches on both sites contained more than one genet. On the older site, the clonal diversity was higher than on the younger site. However, the clonal diversity tended to decrease with increasing patch size. Low genetic differentiation was found between the two sites, indicating habitat differentiation, whereas differentiation between patches within sites was high. It is reasoned that different environmental conditions could have resulted in different clonal structures: On an older marsh, the increase of successful seedling recruitment, due to more suitable environmental conditions, leads to an increase in clonal diversity. Over time, with increasing ramet density, intraspecific competition is likely to increase, resulting in a decrease of clonal diversity.

Abstract: Allozyme markers were used to fingerprint clones of the grassland plant Hieracium pilosella L. and, by inference, to estimate the relative importance of sexual and vegetative reproduction in a population. Field studies in populations of clonal plant species have often reported negligible or absent recruitment from seed. In contrast, studies of genetic markers have found substantial clonal diversity in populations, suggesting recruitment of new genets into established populations. Our results showed that H. pilosella regenerates from seed both within and between dense clonal patches. Two sites differing in environmental conditions were sampled to investigate how the balance between seed-derived and stolon-derived recruitment changes with biotic and abiotic stress. In a relatively drought-prone site on a south-facing slope, the balance was shifted towards recruitment from seed, compared with a mesic site in which vegetative regeneration was more important.