Influence of habitat complexity and landscape configuration on pollination and seed-dispersal interactions of wild cherry trees

Land-use intensification is a major cause for the decline in species diversity in human-modified landscapes. The loss of functionally important species can reduce a variety of ecosystem functions, such as pollination and seed dispersal, but the intricate relationships between land-use intensity, biodiversity and ecosystem functioning are still contentious. Along a gradient from forest to intensively used farmland, we quantified bee species richness, visitation rates of bees and pollination success of wild cherry trees (Prunus avium). We analysed the effects of structural habitat diversity at a local scale and of the proportion of suitable habitat around each tree at a landscape scale. We compared these findings with those from previous studies of seed-dispersing birds and mammals in the same model system and along the same land-use gradient. Bee species richness and visitation rates were found to be highest in structurally simple habitats, whereas bird species richness—but not their visitation rates—were highest in structurally complex habitats. Mammal visitation rates were only influenced at the landscape scale. These results show that different functional groups of animals respond idiosyncratically to gradients in habitat and landscape structure. Despite strong effects on bees and birds, pollination success and bird seed removal did not differ along the land-use gradient at both spatial scales. These results suggest that mobile organisms, such as bees and birds, move over long distances in intensively used landscapes and thereby buffer pollination and seed-dispersal interactions. We conclude that measures of species richness and interaction frequencies are not sufficient on their own to understand the ultimate consequences of land-use intensification on ecosystem functioning.     

Pollination efficiency of wild bees and hoverflies provided to oilseed rape

• 1 Declining numbers in honeybees and various wild bee species pose a threat to global pollination services. The identification and quantification of the pollination service provided by different taxa within the pollinator guild is a prerequisite for the successful establishment of nature conservation and crop management regimes.
• 2 Wild bees and hoverflies are considered to be valuable pollinators in agricultural and natural systems. Although some information on pollination efficiency of individual pollinator species is available, comparative studies of both taxa at different densities are rare. In the present study, the efficiency of the solitary mason bee Osmia rufa and two hoverfly species (Eristalis tenax and Episyrphus balteatus) as pollinators of oilseed rape Brassica napus was examined in a standardized caged plant breeding regime. Honeybee Apis mellifera colonies were used as a reference pollinator taxon.
• 3 Yield parameters responded differently to pollinator density and identity. Fruit set and number of seeds per pod increased with increasing pollinator density, although these were stronger in the mason bee than the hoverfly treatment. Weight per 1000 seeds did not respond to any pollinator treatment, indicating that seed quality was not affected. Oilseed rape yield in the highest tested densities of both pollinator taxa resulted in yield values close to the efficiency of small honeybee colonies.
• 4 Hoverflies required approximately five‐fold densities of the red mason bees to reach a similar fruit set and yield. Thus, mason bees are more efficient in plant breeding and managed pollination systems. Both natural pollinator taxa, however, are of potential value in open and closed crop production systems.

     

Blimp-1Deltaexon7: a naturally occurring Blimp-1 deletion mutant with auto-regulatory potential

Blimp-1 is a master regulator of terminal B cell differentiation and plays a pivotal role in various developmental processes. In addition to full length Blimp-1, a Blimp-1 mRNA lacking exon 7 (Blimp-1Δ7) has been described to occur in murine B cells. The activity and function of the mutant mRNA-encoded protein (Blimp-1Δ7), lacking three crucial zinc fingers necessary for DNA interaction, is completely unknown. Since isoforms of other prdm family proteins affect each other's functions, we wondered whether Blimp-1Δ7 still plays a role in B cells, independent of direct DNA binding. In this study, we found that Blimp-1Δ7 is preferentially expressed in naïve CD19⁺ B cells. A fraction of Blimp-1Δ7 migrates to the nucleus, colocalizes with HDAC2 and is found at sites of repressed chromatin, although it does not bind to the Blimp-1 DNA consensus site. Unexpectedly, Blimp-1 and Blimp-1Δ7 homodimerize as well as heterodimerize with each other. Ectopic expression of Blimp-1Δ7 in WEHI 231 cells, a Blimp-1-negative murine lymphoma line, leads to cessation of proliferation and enhancement of apoptosis. Importantly, LPS-induced differentiation is suppressed in the presence of Blimp-1Δ7. This is in agreement with our finding that Blimp-1Δ7 interferes with endogenous Blimp-1 expression. Thus, our data suggest an auto-regulatory mechanism of Blimp-1 activation.     

Plant attributes determining the regional abundance of weeds on central European arable land

Aim Several recent studies have aimed to identify the biological, ecological and distributional attributes that determine the regional abundance of plant species. Here we aim to assess the relationships between regional abundance and species attributes in weeds on arable land. Location Czech Republic, central Europe. Methods The relationships between regional abundance and species attributes were studied with a data set of 381 weed species occurring on arable land in the Czech Republic. Regional species abundances were estimated from their occurrence frequency in vegetation plots distributed across the country. Using regression tree models, abundance was related to the biological traits, ecological indicator values, geographical distribution and habitat range of species. The models were calculated for the entire country and separately for weeds in cereals, root crops, lowlands and uplands. The effects of phylogenetic relatedness among species on their regional abundance were quantified and compared with the effects of species attributes. Results The results were similar for the whole data set and its particular subsets. Phylogeny explained 11.2–14.9% and species attributes 16.1–56.9% of the variation in regional abundance of weed species. Removal of the phylogenetic signal did not result in important changes in the effects of particular attributes. The most abundant species were those flowering in pre‐spring and early spring, adapted to low temperatures, relatively shade tolerant and with high nutrient requirements. The high regional abundance of these species positively correlated with their broad geographical (often circumpolar) distribution and broad habitat ranges. Main conclusions The regional abundance of weeds can, to some extent, be explained by their attributes. The most important attributes are those that enable weeds to grow and reproduce in the cool season when there is limited competition with crop plants, and those that are adaptations to growth in dense vegetation stands and highly productive habitats.     

Molecular and Genetic Characterization of Propionicin F, a Bacteriocin from Propionibacterium freudenreichii

This work describes the purification and characterization of propionicin F, the first bacteriocin isolated from Propionibacterium freudenreichii. The bacteriocin has a bactericidal activity and is only active against strains of P. freudenreichii. Propionicin F appears to be formed through a processing pathway new to bacteriocins. The mass of the purified bacteriocin was determined by mass spectrometry, and the N-terminal amino acid sequence was determined by Edman degradation. Sequencing of pcfA, the bacteriocin structural gene, revealed that propionicin F corresponds to a 43-amino-acid peptide in the central part of a 255-amino-acid open reading frame, suggesting that mature propionicin F is excised from the probacteriocin by N- and C-terminal proteolytic modifications. DNA sequencing and Northern blot hybridizations revealed that pcfA is cotranscribed with genes encoding a putative proline peptidase and a protein from the radical S-adenosylmethionine family. A gene encoding an ABC transporter was also identified in close proximity to the bacteriocin structural gene. The potential role of these genes in propionicin F maturation and secretion is discussed.     

Effects of landscape context on herbivory and parasitism at different spatial scales

Local community structure and interactions have been shown to depend partly on landscape context. In this paper we tested the hypothesis that the spatial scale experienced by an organism depends on its trophic level. We analyzed plant-herbivore and herbivore-parasitoid interactions in 15 agricultural landscapes differing in structural complexity using the rape pollen beetle ( Meligethes aeneus ), an important pest on oilseed rape ( Brassica napus ), and its parasitoids. In the very center of each landscape a patch of potted rape plants was placed in a grassy field margin strip for standardized measurement. Percent non-crop area of landscapes was negatively related to plant damage caused by herbivory and positively to the herbivores' larval mortality resulting from parasitism. In a geographic scale analysis, we quantified the structure of the 15 landscapes for eight circular sectors ranging from 0.5 to 6 km diameter. Correlations between parasitism and non-crop areas as well as between herbivory and non-crop area were strongest at a scale of 1.5 km, thereby not supporting the view that higher trophic levels experience the world at a larger spatial scale. However, the predictive power of non-crop area changed only slightly for herbivory, but greatly with respect to parasitism as scales from 0.5 to 1.5 km and from 1.5 to 6 km diameter increased. Furthermore, the effect of non-crop area tended to be stronger in parasitism than herbivory suggesting a greater effect of changes in landscape context on parasitoids. This is in support of the general idea that higher trophic levels should be more susceptible to disturbance.     

Strong Synergy between a Eukaryotic Antimicrobial Peptide and Bacteriocins from Lactic Acid Bacteria

The antimicrobial effect obtained upon combining the prokaryotic antimicrobial peptides (AMPs; more commonly referred to as bacteriocins) pediocin PA-1, sakacin P, and curvacin A (all produced by lactic acid bacteria [LAB]) with the eukaryotic AMP pleurocidin (from fish) has been investigated. The three LAB AMPs alone were active against gram-positive Listeria ivanovii bacteria at nanomolar concentrations, whereas they were inactive against gram-negative Escherichia coli bacteria. Pleurocidin alone was active against both of these types of bacteria at micromolar concentrations. Little if any synergy between the LAB AMPs and pleurocidin against the gram-positive L. ivanovii strain was obtained. In contrast, the LAB AMPs and pleurocidin acted highly synergistically against the gram-negative E. coli strain. Nanomolar concentrations of LAB AMPs increased the growth inhibitory potency of pleurocidin by about fourfold. When micromolar concentrations of LAB AMPs were combined with 2 μg of pleurocidin/ml, 100% growth inhibition was attained, whereas pleurocidin alone at a concentration of 2 μg/ml gave no growth inhibition. Most noteworthy, when high concentrations (128 μg/ml) of pleurocidin in the absence of LAB AMPs were used over a long period of incubation (1 week), some growth of E. coli was observed, whereas 16 μg of pleurocidin/ml completely abolished growth in the presence of 64 to 128 ng of LAB AMPs/ml over the same period of time. The results clearly demonstrate that combining eukaryotic and prokaryotic AMPs can greatly increase the specific activity and broaden the target-cell range of these peptides.     

How does landscape context contribute to effects of habitat fragmentation on diversity and population density of butterflies?

Aim Studies on habitat fragmentation of insect communities mostly ignore the impact of the surrounding landscape matrix and treat all species equally. In our study, on habitat fragmentation and the importance of landscape context, we expected that habitat specialists are more affected by area and isolation, and habitat generalists more by landscape context. Location and methods The study was conducted in the vicinity of the city of Göttingen in Germany in the year 2000. We analysed butterfly communities by transect counts on thirty‐two calcareous grasslands differing in size (0.03–5.14 ha), isolation index (2100–86,000/edge‐to‐edge distance 55–1894 m), and landscape diversity (Shannon–Wiener: 0.09–1.56), which is correlated to percentage grassland in the landscape. Results A total of 15,185 butterfly specimens belonging to fifty‐four species are recorded. In multiple regression analysis, the number of habitat specialist (n = 20) and habitat generalist (n = 34) butterfly species increased with habitat area, but z‐values (slopes) of the species–area relationships for specialists (z = 0.399) were significantly steeper compared with generalists (z = 0.096). Generalists, but not specialists, showed a marginally significant increase with landscape diversity. Effects of landscape diversity were scale‐dependent and significant only at the smallest scale (landscape context within a 250 m radius around the habitat). Habitat isolation was not related to specialist and generalist species numbers. In multiple regression analysis the density of specialists increased significantly with habitat area, whereas generalist density increased only marginally. Habitat isolation and landscape diversity did not show any effects. Main conclusions Habitat area was the most important predictor of butterfly community structure and influenced habitat specialists more than habitat generalists. In contrast to our expectations, habitat isolation had no effect as most butterflies could cope with the degree of isolation in our study region. Landscape diversity appeared to be important for generalist butterflies only.