Landscape genetics highlights the role of bank vole metapopulation dynamics in the epidemiology of Puumala hantavirus

Rodent host dynamics and dispersal are thought to be critical for hantavirus epidemiology as they determine pathogen persistence and transmission within and between host populations. We used landscape genetics to investigate how the population dynamics of the bank vole Myodes glareolus, the host of Puumala hantavirus (PUUV), vary with forest fragmentation and influence PUUV epidemiology. We sampled vole populations within the Ardennes, a French PUUV endemic area. We inferred demographic features such as population size, isolation and migration with regard to landscape configuration. We next analysed the influence of M. glareolus population dynamics on PUUV spatial distribution. Our results revealed that the global metapopulation dynamics of bank voles were strongly shaped by landscape features, including suitable patch size and connectivity. Large effective size in forest might therefore contribute to the higher observed levels of PUUV prevalence. By contrast, populations from hedge networks highly suffered from genetic drift and appeared strongly isolated from all other populations. This might result in high probabilities of local extinction for both M. glareolus and PUUV. Besides, we detected signatures of asymmetric bank vole migration from forests to hedges. These movements were likely to sustain PUUV in fragmented landscapes. In conclusion, our study provided arguments in favour of source‐sink dynamics shaping PUUV persistence and spread in heterogeneous, Western European temperate landscapes. It illustrated the potential contribution of landscape genetics to the understanding of the epidemiological processes occurring at this local scale.     

Assessing changes in the genetic diversity of potato gene banks. 1. Effects of seed increase

 Effects of gene bank seed-increases on the genetic integrity of potato germ plasm is a major concern of gene bank managers. Thus the Association of Potato Inter-gene-bank Collaborators (APIC), a consortium of world potato gene bank leaders, initiated this joint research project using RAPD markers to determine genetic relationships between increased generations within accessions. Solanum jamesii (2n=2x=24) and S. fendleri (2n=4x=48), two wild potato species native to North America, were used as plant material. These species represented two major breeding systems found among Solanum species: outcrossing diploids and inbreeding disomic tetraploids, respectively. Comparisons were made between populations one generation apart and between sister populations generated from a common source. Fourteen such comparisons within S. jamesii accessions had an average similarity of 96.3%, and 21 such comparisons within S. fendleri accessions had an average similarity of 96.0%. No pairs of populations were significantly different, despite the fact that RAPD markers easily separated all of these very similar accessions within their respective species. Only one of six S. jamesii accessions analyzed showed a significant change in gene frequencies among generations. These findings indicate that there has been minimal loss or change of genetic diversity in ex situ germplasm using the gene bank techniques standard at NRSP-6 and other world potato gene banks. Received: 28 October 1996 / Accepted: 7 March 1997     

The relationship between the soil seed bank and above-ground vegetation of a coastal barrier island

Abstract. The germinable soil seed bank is described from a coastal barrier island off the northwest coast of Florida, USA. Soil samples collected from seven vegetation types, recently deposited dredge spoil and unvegetated areas in autumn 1990 and spring 1991 were placed out in greenhouse trays. 110 taxa germinated from the samples with the largest number (41) being C₃ perennial dicots. The largest number of taxa germinated from dry (57) and wet (54) swales, the fewest (one species: Heterotheca subaxillaris) from strand. Similarity of seed bank densities to above-ground species cover was low (Jaccard's Index = 0.36), not different between vegetation types, but higher in the autumn than in the following spring. Compositional gradients in the seed bank and above-ground vegetation determined using DCA ordination were highly correlated and related to distance from mean high water, and plot elevation. At the landscape scale, the seed bank provided an equally clear delineation of vegetation types to that based upon the above-ground vegetation. The seed bank of low disturbance, late-succession vegetation types (wooded dunes, swales, marshes) was well developed (high species richness, emergent density, and percentage annual species) with the exception that the large-seeded woody species (i.e. Quercus spp.) were absent from the wooded dune seed bank. By contrast, a poorly developed and transient seed bank occurred in more frequently disturbed (extensive sand movement, salt spray), early successional dredge spoil, unvegetated areas and strand. These contrasts support a general pattern of increasing seed bank development and a persistent rather than transient seed bank with decreasing disturbance frequency, increasing time since disturbance and successional maturity.     

Cloning in E. coli of a streptomyces cellulase gene

Summary A gene bank fromStreptomyces A2, a cellulolytic actinomycete isolated from the gut of termites, has been constructed in theE. coli plasmid pAT153. The clones were screened for their capacity to degrade carboxymethylcellulose by the Congo red and cellulose azure techniques. A plasmid (pCSF1) showing cellulase activity in both tests was isolated and characterized. A restriction map of pCSF1 is reported.     

Seed bank composition and above-ground vegetation in response to grazing in sub-Mediterranean oak forests (NW Greece)

We investigate the persistent soil seed bank composition and its relation to the above-ground flora of grazed and non-grazed sub-Mediterranean deciduous oak forests of NW Greece. Twenty-eight taxa were recorded in the soil seed bank and 83 taxa (70 taxa in plots of seed bank sampling) in the above-ground vegetation. The dominant tree species and many woodland species found in the above-ground vegetation were absent from the soil seed bank. Similarity between the soil seed bank and the above-ground vegetation decreased with grazing, and grazing led to a decrease of species richness in above-ground vegetation and soil seed bank. Beta diversity of vegetation among grazed and among non-grazed plots did not differ, but was significantly higher between grazed and non-grazed areas. Beta diversity of the soil seed bank declined with grazing. When applying classification tree and logistic regression analyses, non-grazed forest sites are clearly differentiated by the presence of Phillyrea latifolia, Euphorbia amygdaloides and Brachypodium sylvaticum. PCA ordination of above-ground species composition reflected a gradient from sites grazed by ruminants to non-grazed sites, but no clear structure was detected in the seed bank.     

Genetic comparisons between seed bank and <Emphasis Type="Italic">Stipa krylovii</Emphasis> plant populations

The soil seed bank represents the potential plant population since it is the source for population replacement. The genetic structure of a Stipa kryiovii (Roshev.) plant population and its soil seed bank was investigated in the Xilinguole Steppe of Inner Mongolia using random amplified polymorphic DNA (RAPD) analyses. The population was sampled at two sites that were in close proximity to each other (0.5 km apart). Thirty plants and 18 seed bank samples were taken from each site to determine the genetic diversity between sites and between sources (plant or seed). The material was analyzed using 13 primers to produce 92 loci. Eighty-six were multi-loci, of which 23 loci (26.74%) of allele frequencies showed significant differences (P ≤ 0.05). The genetic similarity between two seed bank sites was 0.9843 while the genetic similarity between two plant sites was 0.9619. Their similarities were all greater than that between the seed bank and plant populations. An analysis of their genetic structure showed that 87.86% of total variation was derived by two-loci. Genetic structures between plant and soil seed bank populations in S. krylovii were different due to the variance of mean gametic disequilibria and mean gene diversity. AMOVA results showed that the majority of variance (88.62%) occurred within sites, 12.75% was from between-groups. Further research is needed to investigate the selective function in maintaining the genetic diversity of Stipa krylovii plant populations.     

Spatial dynamics of <Emphasis Type="Italic">Ilex aquifolium</Emphasis> populations seed dispersal and seed bank: understanding the first steps of regeneration

The objective of this study was to analyse quantitatively the spatial distribution of holly (Ilex aquifolium L.) seed rain and seed bank, and to detect the relationships between these consecutive processes. We measured seed dispersal by birds and fallen fruits, and also density and viability of seed bank in two Ilex populations in central Spain. Analysis was made distinguishing the following microhabitats: holly woodland, edge of holly woodland, open grassland 10 m and 100 m from the woodland, fleshy fruit shrubs, dry fruit shrubs, and adjacent non-holly woodland. Spatial distribution of dispersed and in-soil seeds was measured by the clumping index. Seed rain and seed bank under holly woodlands were significantly higher than in the other microhabitats. Forest edges and fleshy fruit shrubs were the next microhabitats with the highest seed rain and seed bank density. Interannual and interlocality variations were not significant. The relative importance of the different dispersal methods varied between microhabitats, with a similar support of bird dispersed seeds and fallen fruits within the woodland and a greater influence of cattle dispersal in open areas. Seed spatial aggregation was significant in both dispersed seeds and soil seeds from holly woodlands and the edge of the forest. Aggregation under shrubs, grasslands and the adjacent forests evidenced a general random distribution of holly seeds (only in some cases clumping index was significant). Quantitative differences between seed rain and seed bank are important. Post-dispersal seed predation did not modify seed rain distribution, which was mirrored in the seed bank pattern. These two phases of holly regeneration had a heavy spatial influence, determined by the landscape structure and activity of the dispersal agents, that reflects a differential recruitment potential. Comparisons between both populations suggest that in the southern locality (Robregordo) holly has a weaker capacity to colonize open areas, and a stronger recruitment limitation due to propagule availability.     

Plant species richness and composition of heathland relics in north‐western Belgium: evidence for a rescue‐effect?

Aim To study the effects of the degree of fragmentation of heathland patches on their species richness and species composition, and to infer the ecological mechanisms behind the observed patterns. Location The heathland patches of the north‐western part of Flanders, Belgium. During the last 200 years, the heathland area in this study area has been reduced from c. 10,000 to c. 40 ha, yielding c. 150 small and highly isolated relic fragments. Methods Different isolation measures were calculated for each of the 153 inventoried heathland patches. The influence of isolation, area and habitat diversity on species richness was investigated using correlation techniques. Community composition of the patches was tested for nestedness, and the mechanisms potentially underlying this pattern were determined. Results and main conclusions Both the analyses at the species richness and community composition level yielded evidence for a positive species–area relation. This relation was not caused by higher habitat heterogeneity in larger patches. Patch isolation, measured in different ways, however seemed much more important in explaining species richness and community composition than fragment area. Our results indicate that area effects are overcompensated by the rescue‐effect: if a patch is close to other patches, species can disperse between them and prevent the species from going extinct. Species having a short living seed bank were also more sensitive to isolation than species with a long living seed bank, indicating that the latter most probably depend on the seed bank to survive periods when environmental conditions are harsh. Analogously to the spatial rescue‐effect, the existence of a persistent seed bank may lead to a sort of temporal rescue‐effect, where the extinction of a plant species is prevented through survival in the seed bank of a patch.     

Dermatophytes in a population of bank voles and woodmice

A population of bank voles (Clethrionomys glareolus) and wood mice (Apodemus sylvaticus) inhabiting an oak wood in Somerset was examined for dermatophytes at monthly intervals for 2 years. The marked animals were frequently retrapped, allowing a study of host fungus relationship over a period of time. Microsporum persicolor (Sabouraud) Guiart er Grigorakis and Trichophyton mentagrophytes (Robin) Blanchard were isolated from both animal species, but M. persicolor predominated in bank voles and T. mentagrophytes in wood mice. In their most favoured host, both dermatophyte species often persisted for several months, but in the less favoured host they were never isolated at more than one sampling. Males of both animal species were infected more often than females.The existing evidence for the geophilic nature of both fungi is reviewed and shown to be very weak, especially for M. persicolor.This is the first report from Great Britain of T. mentagrophytes infection of wood mice not in contact with human habitation.     

Development of polymorphic microsatellite markers in sesame (Sesamum indicum L.)

Fifty microsatellite sequences (SSRs) were isolated from an enriched library of sesame (Sesamum indicum L.) using a modified protocol. After screening, 10 polymorphic microsatellites were used to determine their usefulness in diversity analysis among 16 sesame accessions. The number of alleles ranged from three to six alleles per locus with an average of 4.6 alleles. The fragment size varied from 150 bp to 307 bp. Expected heterozygosites (H_E) and polymorphism information contents (PICs) ranged from 0.437 to 0.858 and 0.34 to 0.80, respectively, which indicates the highly informative nature of the microsatellites reported here. These microsatellite markers will be very useful in diversity analysis among a large germplasm collection of sesame present in our Korean gene bank and also in the establishment of its core collection.     

POPULATION BIOLOGY OF BONAMIA GRANDIFLORA (CONVOLVULACEAE): EFFECTS OF FIRE ON PLANT AND SEED BANK DYNAMICS

The effects of disturbance on reproduction and plant and seed bank dynamics in the perennial herb Bonamia grandiflora were studied by comparing populations in recently burned, mechanically disturbed, and undisturbed habitats in central Florida over a 3-year period. Plant densities, seed production, and the occurrence of herbivory and predispersal seed predation varied considerably between sites and between years, with recently disturbed sites supporting the densest and most dynamic populations. Death of established plants was rare in all sites. In each site, the soil seed bank was several-fold larger than single season seed rains suggesting that B. grandiflora seeds are long-lived and accumulate in the soil. There was no evidence that postdispersal predation or pathogens have any significant influence on the seed bank dynamics. Fire resulted in large increases in stem densities due to both increased clonal stem production and new genet recruitment from seed. Burning also caused significant increases in the percentage of flowers producing seed and the numbers of capsules and seeds per plant. The seed rain was ten to thirty times greater in the burned site relative to adjacent unburned site during the 3 years after burning. However, additions to the seed bank from the postfire seed rain were balanced by equivalent losses due primarily to seed mortality during fire, and to a much lesser extent due to germination and new genet establishment. As a result, the subsequent densities of seeds stored in the soil in these two sites were similar, indicating that fire results in a significant turnover in the seed bank population but no immediate change in its size. These effects on seed bank dynamics, in addition to new genet recruitment, suggest that periodic fires may play an important role in the maintenance of genetic variability as well as the size of these populations.     

A large panel of novel microsatellite markers for the bank vole (Myodes glareolus)

We describe a set of 66 highly polymorphic microsatellite loci isolated from the bank vole, Myodes (Clethrionomys) glareolus. These microsatellites were characterized for a long-term study on periodically fluctuating density of the bank vole population in Central Finland. We detected six to 38 alleles per locus in the population sampled at two different density phases, and the levels of observed and expected heterozygosities varied between 0.17 and 1.00, and between 0.72 and 0.95, respectively. This microsatellite panel serves as an informative tool for population and molecular genetic studies.     

Effect of light stress from phytoplankton on the relationship between aquatic vegetation and the propagule bank in shallow lakes

1. The way light stress controls the recruitment of aquatic plants (phanerogams and charophytes) is a key process controlling plant biodiversity, although still poorly understood. Our aim was to investigate how light stress induced by phytoplankton, that is, independent from the aquatic plants themselves, determines the recruitment and establishment of plant species from the propagule bank. The hypotheses were that an increase in light stress (i) decreases abundance and species richness both of established aquatic plants and of propagules in the bank and (ii) decreases the recruitment success of plants from this bank. 2. These hypotheses were tested in 25 shallow lakes representing a light stress gradient, by sampling propagule banks before the recruitment phase and when the lakes are devoid of actively growing plants (i.e. at the end of winter), established vegetation at the beginning of the summer and phytoplankton biomass (chlorophyll a) during the recruitment and establishment phase. 3. The phytoplankton biomass was negatively correlated with the richness and abundance of established vegetation but was not correlated with the propagule bank (neither species richness nor propagule abundance). The similarity between the propagule bank and established vegetation decreased significantly with increasing phytoplankton biomass. 4. The contrast in species composition between the vegetation and the propagule bank at the highest light stress suggests poor recruitment from the propagule bank but prompts questions about its origin. It could result from dispersal of propagules from neighbouring systems. Propagules could also originate from a persistent propagule bank formerly produced in the lake, suggesting strong year‐to‐year variation in light stress and, as a consequence, in recruitment and reproductive success of plants.     

Does invasion by an alien plant species affect the soil seed bank?

Questions: How does invasion affect old‐field seed bank species richness, composition and density? How consistent are these effects across sites? Does the soil seed bank match vegetation structure in old‐fields? Location: Menorca, Balearic Islands, Spain, western Mediterranean basin. Methods: We monitored seed germination in soils from old‐fields that were both uninvaded and invaded (legacy effect) by the annual geophyte Oxalis pes‐caprae. We also added O. pes‐caprae bulbs to uninvaded soils to test O. pes‐caprae interference with seedling emergence (competitive effect). We compared species composition in the seed bank with that of the vegetation. Results: Species richness in the seed bank and in the vegetation was not significantly different between invaded and uninvaded areas. Uninvaded areas did not have larger seed banks than invaded areas. More seedlings, especially of geophytes, emerged when O. pes‐caprae bulbs were added to the soil. Species similarity between invaded and uninvaded areas was higher in the seed bank (74%) than in the vegetation (49%). Differences in species composition were as important as differences among sites. The degree of species similarity between the seed bank and the vegetation was very low (17%). Conclusions: Despite invasion by O. pes‐caprae not affecting species richness, the variation in the seed bank species composition in invaded and uninvaded areas, and the differences between the seed bank and the mature vegetation, highlights that even if the invader could be eradicated the vegetation could not be restored back to the exact composition as found in uninvaded areas.     

Leeward bank margin Halimeda meadows and draperies and their sedimentary importance on the western Great Bahama Bank slope

Bryopsidalean algal meadows in water depths of 20–40 m on the leeward side of western Great Bahama Bank (WGBB) lie between non-skeletal-dominated sand flats on the bank top to the east and a cemented steep escarpment to the west. The meadows contain dense populations of rhipsalian Halimeda species, as well as Udotea and Rhipocephalus. Extensive populations of other Halimeda species (opuntioids) occur at greater depths on the cemented rocky escarpment, growing as drapes or vines rather than as upright thalli. These meadows and draperies are important sources of coarse-grained carbonate sediments. This is shown by (1) deeper bank-edge sediments (30–60 m) containing considerably more Halimeda fragments than do the bank top, non-skeletal sands, and (2) the coarser fraction of slope sediments (down to 200 m) dominated by Halimeda plates, partly or extensively altered and internally cemented by magnesian calcite and aragonite. A transect across the bank margin from bank top (<10 m) to lower slope (300 m) provides a useful comparison for the locus of sediment production and accumulation. The production of Halimeda in these bank-edge habitats approximates that in the Great Barrier Reef or off Indonesia and Nicaragua in similar water depths. The apparent lack of thick sediment accumulation in WGBB compared to that seen elsewhere may reflect the high rates of downslope transport off Great Bahama Bank.     

洮河上游紫果云杉群落土壤种子库特征及其与地上植被的关系

该研究以甘肃洮河国家级自然保护区大峪沟林区(TH)、冶力关林区(YLG)、尕海 则岔国家级自然保护区则岔林区(GZ)的紫果云杉(Picea purpurea)天然林群落为研究对象,通过样地调查与萌发实验,分析洮河上游紫果云杉群落土壤种子库特征,以揭示洮河上游紫果云杉群落土壤种子库特征及与地上植被的关系,为紫果云杉群落恢复和管理提供依据。结果表明：(1)3个林区土壤种子库共萌发27科45属50种植物,种子库密度在958~1 129粒/m²之间,草本植物是构成研究区土壤种子库的主体。(2)3个林区紫果云杉群落土壤种子库垂直结构明显,物种数及种子密度随土层的加深呈减少趋势。(3)3个林区地上植被物种数大于土壤种子库物种数,相似性系数在0.15~0.23之间,表现为极不相似性;土壤种子库的多样性指数除Pielou指数高于地上植被外,Margalef指数、Shannon Wiener指数、Simpson指数均低于地上植被。研究认为,洮河上游紫果云杉群落土壤种子库以草本植物为主,乔木和灌木的储量较小,特别是建群种紫果云杉的储量较小;地上植被和土壤种子库之间相互的贡献力较低,仅依靠紫果云杉林土壤种子库进行自然恢复,远不能缓解现阶段紫果云杉林退化的问题,因此需开展人工育苗、造林等措施来促进紫果云杉的更新与发展。     

Restoration potential of invaded abandoned agricultural fields: what does the seed bank tell us?

Soil seed banks can play an important role in the restoration of degraded ecosystems, especially where indigenous species are well represented in, and invasive species are largely absent from, the seed bank. Here, we studied the potential contribution of the soil seed bank to the restoration of invaded, abandoned agricultural fields in the Eastern Cape, South Africa. We recorded the aboveground cover and belowground abundance of all vascular plant species from 120 quadrats that differ in cover of the extralimital woody invader, Pteronia incana. Our results show that higher cover of P. incana is associated with lower species richness, aboveground cover, and belowground seed abundance. Furthermore, community similarity between the above‐ and belowground component was low, with the seed bank and standing vegetation having only 15 species in common and 49 species being recorded only from the seed bank. We suggest that this large number of seed bank‐only species is a relic of previous vegetation, prior to large‐scale invasion by P. incana. The most important finding from our study is the absence of P. incana from the soil seed bank. This finding, combined with the large number of mostly native species from the seed bank, holds promise from a restoration perspective. However, given the susceptibility of the invaded systems to erosion, coupled with the low grazing value of the seed bank species, we suggest that P. incana removal should be accompanied by both erosion control measures and reseeding with palatable grass species, to secure the livelihoods of local communities.     

Gene conversion in the mitochondrial genome on interspecific hybridization in voles of the <Emphasis Type="Italic">Clethrionomys</Emphasis> genus

The phenomenon of interspecific hybridization accompanied by transfer of the mitochondrial genome from the northern red-backed vole (Clethrionomys rutilus) to the bank vole (Cl. glareolus) in northeastern Europe is well known already for 25 years. However, the possibility of recombination between homologous segments of maternal and paternal mtDNAs of the voles during fertilization was not previously studied. Analysis of data on variability of nucleotide sequences of the mitochondrial gene for cytochrome b in populations of red-backed and bank voles in the area of their sympatry has shown that as a result of interspecific hybridization, the mitochondrial gene pool of bank voles contains not only mtDNA haplotypes of red-backed vole females, but also mtDNA haplotypes of bank voles bearing short nucleotide tracts of red-backed vole mtDNA. This finding supports the hypothesis that an incomplete elimination of red-backed vole paternal mtDNA during the interspecific hybridization between bank vole females and red-backed vole males leads to the gene conversion of bank vole maternal mtDNA tracts by homologous ones of mtDNA of red-backed vole males.     

Diet differentiation between European arvicoline and murine rodents

Small European muroid rodents are generally divided into species which feed on seeds and/or invertebrates and species which feed on green plant material; however, there is considerable plasticity in feeding behavior among species. Here, we analyze diets of 14 low-latitude rodent species from Western Europe based on published studies. The 77 studies were submitted to principal component analysis in order to compare diet plasticity within and between the 14 species. We observed variations in food composition of arvicoline and murine rodents which are associated with differences in morphology and habitat use. Most arvicoline rodents eat mainly green matter of the herbaceous layers of open habitats whereas most murine species are able to use a greater diversity of high energetic plant tissues from denser habitats, where they can exploit the different vegetation layers. Despite its phylogenetic position among arvicoline rodents, the bank vole (Myodes glareolus) shows morpho-physiological and ecological traits which tend to be more similar to murine species. These intermediate evolutionary characters seem consistent with the fact that bank voles are able to exploit a wide spectrum of trophic resources from low energetic lignified tissues to high calorific invertebrate prey. This results in a very diverse diet, which is intermediate between true herbivorous arvicolines and typical seed- and invertebrate-eating murine species. More investigations on genetic affiliation and ecological driving forces will help understand this intermediate position of bank vole diet, and further investigations among other arvicoline species will help determine if bank voles and other Myodes species are unique.     

Examining the bank of microscopic stages in kelps using culturing and barcoding

This paper describes a method to study the diversity of young kelp sporophytes that are recruited from the bank of microscopic stages. Small samples of rocky substratum (0.5 cm²) were collected from the low intertidal zone, which was dominated by the kelp Laminaria digitata. Samples were cultivated in the laboratory under conditions permitting gametogenesis. Sporophyte recruits in the cultures were isolated and identified at the species level using the barcoding mitochondrial marker rpl31–rns. Sixty per cent of the collected samples had at least one to a maximum of 30 kelp recruits, belonging to five different species (L. digitata, L. hyperborea, L. ochroleuca, Saccharina latissima and Sacchorhiza polyschides). As the examination of freshly collected rocky samples under a stereo microscope did not reveal any kelp sporophytes, the recruitment in these samples after culture probably occurred from the bank of microscopic forms present on the substratum. Despite the dominance of L. digitata in the field, the young sporophytes obtained after culturing were mainly S. polyschides. This study illustrates the suitability of culturing in combination with molecular identification of young sporophytes to address several key aspects of kelp ecology related to the existence of a bank of microscopic stages in the field.