Population genetic structure of the tree-hole tick Ixodes arboricola (Acari: Ixodidae) at different spatial scales

The endophilic tick Ixodes arboricola infests cavity-nesting birds, and itsdispersal strongly depends on the movements of its host. Population genetic structureof I. arboricola was studied with seven polymorphic microsatellite markers.We collected 268 ticks from 76 nest boxes in four woodlots near Antwerp, Belgium.These nest boxes are mainly used by the principal hosts of I. arboricola,the great tit Parus major and the blue tit Cyanistes caeruleus. Asthese birds typically return to the same cavity for roosting or breeding, tickswithin nest boxes were expected to be highly related, and tick populations wereexpected to be spatially structured among woodlots and among nest boxes withinwoodlots. In line with the expectations, genetic population structure was found amongwoodlots and among nest boxes within woodlots. Surprisingly, there was considerablegenetic variation among ticks within nest boxes. This could be explained bycontinuous gene flow from ticks from nearby tree holes, yet this remains to betested. A pairwise relatedness analysis conducted for all pairs of ticks within nestboxes showed that relatedness among larvae was much higher than among later instars,which suggests that larvae are the most important instar for tick dispersal. Overall,tick populations at the studied spatial scale are not as differentiated as predicted,which may influence the scale at which host–parasite evolution occurs.     

Auxin in scapes,flower buds,flowers, and fruits of daffodil (Narcissus pseudonarcissus L.)

Summary Diffusates from flower buds, flower fruits, and scape segments, and extracts of flower stalks of Narcissus pseudonarcissus contain an auxin active in the Avena geo-curvature test. The auxin behaved like indole-3-acetic acid (IAA) in thin-layer chromatography (TLC) with neutral and basic solvents on different adsorbents. After TLC, the auxin of the extracts showed chromogenic reactions identical with those of IAA; in gas-liquid chromatography on two different columns, the purified substance, after methylation, appeared at the retention time of IAA methyl ester. The auxin content of the extracts has been estimated to be equivalent to ca. 10 g IAA kg^–1 fresh weight. Diffusates, collected at the basal end of excised flowering apices and of scape segments at different developmental stages, showed highest auxin activity when collected from old buds and young flowers, and from the basal, rapidly elongating scape regions. The diffusible auxin obtained from scape segments was very likely produced by the segments themselves. Thus, the shoot of Narcissus appears to possess two different sites of auxin production, namely, the apical region represented by the flower bud, the flower or the fruit, and the scape.Abbreviations IAA indole-3-acetic acid - IAA-OMe indole-3-acetic-acid methyl ester - TLC thin-layer chromatography - GLC gas-liquid chromatography     

Community structure in ichneumonid parasitoids at different spatial scales

The processes underlying parasitoid community structure are little known. Stochastic niche-apportionment models provide one route to underlying assemblage rules in this and other groups. Previous work has applied this approach to parasitoids found on single host species in single populations. However, parasitoid communities are known to extend across multiple hosts and scales. The patterns of relative abundances generated by five niche-apportionment models were compared to those observed in assemblages of two sub-families of the Ichneumonidae, the Diplazontinae and Pimplinae, at landscape and patch scales, Yorkshire, UK. Three of the five models produced patterns that were significantly different to the observed pattern for all taxonomic levels at both spatial scales. The Diplazontinae fit the random fraction (RF) model at the landscape scale in broadleaved woods. This suggests that hierarchical structuring and biotic interactions may play a role in the structuring of Diplazontinae assemblages at this scale. In contrast the Pimplinae fit the RF model only at the patch scale and only at one site. However, the Pimplini tribe (all chiefly parasitoids of Lepidoptera) fit the random assortment (RA) model at both the landscape and the patch scales, whilst the Ephialtini tribe (wide range of hosts) fit no model at either scale. The ecological interpretation of the RA model suggests that the Pimplini tribe is an unsaturated assemblage, where some of the total available resources are unused. Our results show, through the fit of mechanistic niche-apportionment models, that the processes that may structure ichneumonid parasitoid assemblages are not consistent across taxa and spatial scales.     

Variation of a floral polymorphism at different spatial scales in the Mediterranean geophyte Narcissus assoanus

Aims Habitat fragmentation impacts the spatial extent and isolation of local populations and communities. Although the biological consequences of these impacts have been well studied at the site level, effects directly related to changes in the spatial configuration of populations in the landscape remain less clear. The objective of this study is to examine how changes in the spatial-scale configuration of populations are associated with variability in morph rations in the floral polymorphic Mediterranean geophyte Narcissus assoanus .Methods We performed a nested analysis of morph ratio variation at three spatial scales: a 50×50 km regional scale in SE France, in fourteen 1×1 km landscapes located in the same region, and within 12 spatially extensive population patches. We also quantified variation in the behaviour of pollinators in population patches of contrasting spatial configuration.Important findings At a regional scale, morph ratios show a geographic pattern of increasing isoplethy (1:1 morph ratio) away from centres of human population development and in upland pastures. At the landscape scale, isoplethy of local population patches is more correlated with decreased isolation among patches than with patch size. Finally, within local isoplethic populations, small patches can show significantly biased morph ratios. In small isolated patches, pollinators perform shorter flight distances among consecutive flower visits than in spatially extensive patches. This study of variation in a genetic polymorphism at multiple spatial scales provides new insights into the scale-dependent effects of habitat fragmentation and the potential occurrence of metapopulation dynamics in natural plant populations.     

The site of carotenogenic enzymes in chromoplasts from Narcissus pseudonarcissus L.

The membranes from the chromoplasts of Narcissus pseudonarcissus L. which are derived from the inner envelope membrane are the site of -carotene synthesis from [1-¹⁴C]isopentenyl diphosphate. The enzymes involved are partly peripheral membrane proteins (prenyltransferase, phytoene synthase) and partly integral membrane proteins (cis-trans isomerase, dehydrogenase(s), cyclase(s)). Metabolic channeling is suggested.Abbreviations IPP isopentenyl diphosphate - GGPP geranylgeranyl diphosphate     

The evolution of polymorphic sexual systems in daffodils (Narcissus)

Narcissus, the daffodil genus, exhibits an unusual diversity of sexual systems, with populations that are monomorphic, dimorphic or trimorphic for style length. Associated with this variation are striking differences among species in floral morphology and pollination biology. This diversity provides an opportunity to investigate the evolution of mating polymorphisms, and to determine how floral morphology promotes transitions among sexual systems. Because of the absence of heteromorphic incompatibility in Narcissus, floral morphology plays a key role in governing patterns of outcrossed mating. Phylogenetic evidence indicates that stylar monomorphism is ancestral in the genus, with multiple origins of stylar polymorphism, including independent origins of stigma-height dimorphism, distyly and tristyly. Sexual polymorphisms have evolved only in lineages with narrow floral tubes that are pollinated by Lepidoptera and/or long-tongued bees. Populations of polymorphic Narcissus species are typically dominated by the long-styled morph and display imperfect reciprocity in the positions of sexual organs. These features are consequences of the unusual association between stylar polymorphism and a self-incompatibility system that permits intramorph mating.     

Spatial genetic structure in wild cherry (Prunus avium L.): II. Effect of density and clonal propagation on spatial genetic structure based on simulation studies

We conducted simulations to disentangle the effect of density and clonal propagation on spatial genetic structure and genetic diversity parameters in Prunus avium. In a previous paper, we observed stronger family structure in populations exhibiting high density and high clonal propagation, whereas one low-density and low clonal propagation population showed negative spatial autocorrelation. We tried to understand these results by simulating 200 years of growth, mating and dispersal with the model Eco-Gene, using two levels of density and three levels of clonal propagation in one high-density population (Spargründe) and one low-density population (Chorin). We used allele frequencies from eight microsatellite loci to generate the populations used for simulations. In order to detect effects of the initial structure on the results, we also ran the simulations starting from the real data. We observed positive effect of clonal propagation on the strength of SGS, while high densities exhibited a negative impact. Genetic diversity was maintained at high densities, while pollen dispersal was shorter. Heterozygosity increased at higher clonal propagation rates, although genetic diversity (accumulated number of genotypes) was lower. We discuss the results according to mating processes and potential management scenario.     

Spatial genetic structure in wild cherry (Prunus avium L.): I. variation among natural populations of different density

Conservation of forest genetic resources requires intensive knowledge of the spatial arrangement of genetic diversity. In this study, we used four natural Prunus avium stands in Germany with contrasting for densities to understand patterns of spatial genetic structure. To this end, we genotyped adults and saplings at eight microsatellite markers, 54 AFLP loci and at the gametophytic incompatibility locus. We estimated levels of clonal propagation, spatial genetic structure and gene dispersal. High mortality occurred among young clonal individuals, as depicted by the lower clonal diversity in saplings. Contrasting levels of spatial genetic structure were observed among markers, ontogenic stages and populations. AFLP were more efficient for detecting spatial autocorrelation but did not allow us to differentiate low and high density populations, while high density populations showed substantially stronger spatial genetic structure at microsatellite loci. Furthermore, kinship decreased with tree age only in low density stands. We discuss the present results in terms of population history, pollen and seed dispersal and population density. Although conspecific density seems to be an interesting indicator of genetic diversity for conservation programmes, we still need to disentangle the relative influence of clonal propagation and density on the strength of spatial genetic structure. Simulation studies are needed to further address this question.     

Population genetic structure of three freshwater mussel (Unionidae) species within a small stream system: significant variation at local spatial scales

1. Unionid mussels are highly threatened, but little is known about genetic structure in populations of these organisms. We used allozyme electrophoresis to examine partitioning of genetic variation in three locally abundant and widely distributed species of mussels from a catchment in Ohio. 2. Within‐population variation was similar to that previously reported for freshwater mussels, but genotype frequencies exhibited heterozygote deficiencies in many instances. All three species exhibited significant among‐population variation. Evidence of isolation‐by‐distance was found in Elliptio dilatata and Ptychobranchus fasciolaris, while Lampsilis siliquoidea showed no geographical pattern of among‐population variation. 3. Our results suggest that the isolating effects of genetic drift were greater in L. siliquoidea than in the other species. Differentiation of populations occurred at a much smaller spatial scale than has previously been found in freshwater mussels. Differences among species may reflect differences in the dispersal abilities of fishes that serve as hosts for the glochidia larvae of mussels. 4. Based on our results, we hypothesise that species of mussels that are common to large rivers exhibit relatively large amounts of within‐population genetic variation and little differentiation over large geographical distances. Conversely, species typical of small streams show lower within‐population genetic variation and populations will be more isolated. If this hypothesis can be supported, it may prove useful in the design of conservation strategies that maintain the genetic structure of target species.     

Bark beetle diversity at different spatial scales

To determine how the scale of observation affects ecological patterns we studied bark beetle (Coleoptera, Scolytidae) diversity in southern Finland. A block covering 160 × 160 m of a forest was delimited in four stands of different site types. Each block was divided into 256 squares (10 × 10 m) in which the occurrence of bark beetle species was recorded. In addition, environmental variables describing site type, trees, and breeding material appropriate for bark beetles were measured. The species presence/absence data were combined at different scales of resolution (10 × 10 m. 20 × 20 m, 40 × 40 m, 80 × 80 m, 160 × 160 m). At the finest scale a recently thinned pine stand showed relatively high diversity compared to other study stands due to a few evenly distributed and abundant species. However, the species diversity increased faster toward larger scales in mature spruce stands with several sporadically distributed species. According to logistic regression analyses, breeding material and site characteristics explained the occurrence of most beetle species. However, these variables did not explain the occurrence of the six most frequent species, probably because the factors regulating their distribution and occurrence operate at larger scales.     

Topographic influences on radial growth of Scots pine (Pinus sylvestris L.) at small spatial scales

Dendroecological and numerical methods were used to study the influence of topographic position on radial growth of Scots pine (Pinus sylvestris) stands exposed to soil dryness. The correlation structure of total tree-ring width and latewood width of eight scattered populations representing various topographic habitats (steep south-facing slopes, plateaus and hollows) within a rock-slide area (750 m a.s.l.) of about 1 km² was investigated by principal component analysis. Scatter plots of component loadings indicated that (i) total ring width and latewood width are influenced by various climatic factors, (ii) stands growing at similar topographic position show a high agreement in year-to-year variability of radial growth, and (iii) distinct effects of topographic features (slope aspect, slope magnitude) on tree growth are modified by local disturbances (erosion, grazing) and the age structure of stands. Furthermore, both the time series of component scores and non-metric multidimensional scaling of chronologies indicated years where extremely limiting or favorable climate conditions prevailed throughout the study area (pointer years). The influence of climate on tree growth in various topographic habitats was mediated through the influence of climatically stressful years. Because stands are located at sites with different levels of water stress, growth differences between chronologies are considered to be caused by site-specific susceptibility of tree growth to soil dryness. Significant correlations between precipitation in April to June and ring-width confirm that water availability is the primary growth-limiting factor within the study area. These small-scale variations in growth-climate relationships have significant implications for dendroclimatological studies. So paleoclimatic reconstructions based on tree rings will have to assure that an unbiased data set is used, which compensates for local growth-variabilities due to site related environmental stresses.     

Zur Verbreitung der gelben Narzisse (Narcissus pseudonarcissus L.) auf Primär- und Sekundärstandorten in Mittel- und Nordwesteuropa

N. pseudonarcissus und N. poeticus kommen in Nordwest- und Mitteleuropa sekundär in armen Triseteten und Arrhenathereten vor. N. pseudonarcissus hat weitere Vorkommen im Calthion, Molinion und Nardo-Galion; N. poeticus im Mesobromion. Primärstandorte von N. poeticus sind im Caricion ferrugineae, von N. pseudonarcissus im Calamagrostion arundinaceae zu finden Förderlich für die Entwicklung von N. pseudonarcissus ist ein ausgeglichenes Klima mit kühlen Sommern und milden Wintern Auf Grünlandstandorten wird N. pseudonarcissus durch einen phänologi-schen Vorsprung vor den anderen Wiesenarten gefördert; es ist dabei gleichgültig, ob dieser durch Wiesenbewässerung, durch “natural mulch” oder durch ein atlantisches Klima erreicht wird N. pseudonarcissus kommt in Wäldern im Acerion der Vogesen und in Niederwäldern der Ardennen vor. Auch hier ist die bodenklimatische Begünstigung in Abhängigkeit vom Waldtyp und der Exposition der ökologisch wichtigste Faktor     

Comparative analysis of the within-population genetic structure in wild cherry (Prunus avium L.) at the self-incompatibility locus and nuclear microsatellites

Gametophytic self-incompatibility (SI) systems in plants exhibit high polymorphism at the SI controlling S-locus because individuals with rare alleles have a higher probability to successfully pollinate other plants than individuals with more frequent alleles. This process, referred to as frequency-dependent selection, is expected to shape number, frequency distribution, and spatial distribution of self-incompatibility alleles in natural populations. We investigated the genetic diversity and the spatial genetic structure within a Prunus avium population at two contrasting gene loci: nuclear microsatellites and the S-locus. The S-locus revealed a higher diversity (15 alleles) than the eight microsatellites (4-12 alleles). Although the frequency distribution of S-alleles differed significantly from the expected equal distribution, the S-locus showed a higher evenness than the microsatellites (Shannon's evenness index for the S-locus: E = 0.91; for the microsatellites: E = 0.48-0.83). Also, highly significant deviations from neutrality were found for the S-locus whereas only minor deviations were found for two of eight microsatellites. A comparison of the frequency distribution of S-alleles in three age-cohorts revealed no significant differences, suggesting that different levels of selection acting on the S-locus or on S-linked sites might also affect the distribution and dynamics of S-alleles. Autocorrelation analysis revealed a weak but significant spatial genetic structure for the multilocus average of the microsatellites and for the S-locus, but could not ascertain differences in the extent of spatial genetic structure between these locus types. An indirect estimate of gene dispersal, which was obtained to explain this spatial genetic pattern, indicated high levels of gene dispersal within our population (sigma(g) = 106 m). This high gene dispersal, which may be partly due to the self-incompatibility system itself, aids the effective gene flow of the microsatellites, thereby decreasing the contrast between the neutral microsatellites and the S-locus.     

A low-density single nucleotide polymorphism panel for brown trout (Salmo trutta L.) suitable for exploring genetic diversity at a range of spatial scales

The rivers of southern England and northern France which drain into the English Channel contain several genetically unique groups of trout (Salmo trutta L.) that have suffered dramatic declines in numbers over the past 40 years. Knowledge of levels and patterns of genetic diversity is essential for effective management of these vulnerable populations. Using restriction site-associated DNA sequencing (RADseq) data, we describe the development and characterisation of a panel of 95 single nucleotide polymorphism (SNP) loci for trout from this region and investigate their applicability and variability in both target (i.e., southern English) and non-target trout populations from northern Britain and Ireland. In addition, we present three case studies which demonstrate the utility and resolution of these genetic markers at three levels of spatial separation:(a) between closely related populations in nearby rivers, (b) within a catchment and (c) when determining parentage and familial relationships between fish sampled from a single site, using both empirical and simulated data. The SNP loci will be useful for population genetic and assignment studies on brown trout within the UK and beyond.     

Population genetic structure of brown trout (Salmo trutta L.) within a northern boreal forest stream

Brown trout (Salmo trutta L.) population genetic structure and its temporal stability were studied within a small forest stream in central Sweden using five microsatellite loci. Both resident and migrating brown trout are present in the watershed. Tissue samples were collected from seven sections of the stream during two consecutive years. No differences were found in multilocus FST estimates between years within sections except in one case. Moreover, differences between age cohorts within sample sections were rare. The low interannual variation and the low heterogeny between cohorts is interpreted as indications of temporal stability. Pairwise multilocus FST estimates increased with increasing geographic distance, indicating isolation by distance. It is argued that the brown trout of the F?rs?n stream represent a population complex. The structure is probably maintained by precise natal homing and a limited, but important, amount of gene flow between closely situated sections within the stream supporting a stepping-stone model of gene flow.     

Population genetic structure of Arctic charr, Salvelinus alpinus from northwest Europe on large and small spatial scales

To examine the population genetic structure of lake-resident Arctic charr, Salvelinus alpinus from northwest Europe on multiple spatial scales, 2367 individuals from 43 lakes located in three geographical regions (Iceland, the British Isles and Scandinavia) were genotyped at six microsatellite loci. On a large scale, data provided little evidence to support clustering of populations according to geographical region. Hierarchical analysis of molecular variance indicated that, although statistically significant, only 2.17% of the variance in allelic frequencies was partitioned at the among-region level. Within regions, high levels of genetic differentiation were typically found between lakes regardless of the geographical distance separating them. These results are consistent with the hypothesis of rapid postglacial recolonization of all of northwest Europe from a single charr lineage, with subsequent restriction of gene flow. On a smaller scale, there was evidence for close genetic relationships among lakes from within common drainage basins in Scotland. Thus, interlake genetic structure reflects localized patterns of recent (or contemporary) gene flow superimposed onto a larger scale structure that is largely a result of historical processes. There was also evidence for widespread genetic structuring at the within-lake level, with sympatric populations detected in 10 lakes, and multilocus heterozygote deficits found in 23 lakes. This evidence of the Wahlund effect was found in all lakes known to contain discrete phenotypic morphs, as well as many others, suggesting that morphs may often represent separate breeding populations, and also that the phenomenon of polymorphism in this species may be more widespread than is currently realized.     

Variation in invertebrate–bryophyte community structure at different spatial scales along altitudinal gradients

Aim This study assessed changes in diversity and assemblage composition in bryophytes and their associated invertebrates along altitudinal gradients in Australia and New Zealand. The importance of altitude in shaping these communities and for the diversity of both invertebrates and bryophytes was examined at different spatial scales, including local, altitudinal, regional and biogeographical. Location Samples were taken from four Australasian mountain ranges between 42° and 43°S: Mt Field and Mt Rufus, Tasmania, Australia, and Otira Valley and Seaward Kaikoura Mountains, South Island, New Zealand. Methods On both Tasmanian mountains, five altitudes were assessed (250, 500, 750, 1000 and 1250 m). At each location (mountain/altitude combination) two sites were chosen and six samples were taken. Six altitudes were assessed on New Zealand mountains (Otira: 250, 500, 750, 1000, 1250 and 1500 m; Kaikoura: 1130, 1225, 1325, 1425, 1525 and 2000 m). Bryophyte substrate was collected, and all samples were stored in 70% ethanol. Invertebrates were extracted from bryophytes using kerosene‐phase separation and all invertebrates were identified to family. At each location in Tasmania, all bryophyte species within six 25‐cm² grids per site were collected and identified to species. Bryophytes from New Zealand were identified to species from the invertebrate sample substrate because of sampling constraints. Results Altitude did have a significant effect on diversity, however, no general trend was found along the altitudinal gradient on the four mountains. There were distinct differences in diversity between biogeographical regions, mountains, altitudes and sites. In Tasmania, Mt Field had the highest diversity in invertebrates and bryophytes at 750 m. In contrast, Mt Rufus had consistent low invertebrate and bryophyte diversity along the entire altitudinal gradient. There were also distinctive differences between locations in the composition of invertebrate and bryophyte communities in Tasmania. Along the two altitudinal gradients in New Zealand, Otira had highest diversity for both invertebrates and bryophytes at low altitudes, whereas Kaikoura had highest invertebrate and lowest bryophyte diversity at the highest altitude. Main conclusions There was an effect of altitude, however, there were no consistent changes in diversity or composition on the four different mountains. There was considerable local and regional variation, and, despite a strong sampling design, no underlying altitudinal trends were detectable. This study demonstrates the importance of examining a range of spatial scales if patterns in community structure along altitudinal gradients are to be studied. The implications of this study are discussed with reference to survey design, taxonomic resolution, climate change and conservation of habitat.     

Interactions of gall-forming species at different plant spatial scales

Interspecific competition has been intensely studied as an organizing force in insect herbivore communities that can be mediated by changes in resource availability. We analyzed patterns of interspecific association of three species of gall-forming insects at shoot length class and shrub levels for Bauhinia brevipes through a null model program. Results show that shoots galled by three species were distributed independently among shoot length classes over 3-years, hence, no evidence of competition for shoots was found. Nevertheless, at the plant level our results suggest that there was a positive association. We found no evidence of any reciprocal negative effect because the density of species did not differ among shoot length classes. We suggest that this lack of pattern was probably due to: (a) host-plant resistance mediating interactions; (b) higher abundance of plant resource available, or (c) free-feeding herbivores mediating interactions by manipulating the resources used by gall-forming species.