Reproductive biology of twoPrunus species (Rosaceae) in the Northwest Iberian Peninsula

We studied the reproductive biology ofPrunus spinosa andPrunus mahaleb (Prunoideae, Rosaceae) in the northwest Iberian Peninsula. The two species flowered at the same time (peaking on March 9 and 11, respectively in 1990) but differ significantly in their fruit maturation times. Nectar volume peaked in the early morning in both species, and was ten times greater inP. spinosa than inP. mahaleb. Neither species shows apomixis, nor does fruit-set occur if pollinators are excluded. In both species self-pollination resulted in fewer fruits than open pollination. The principal pollinators belong to theApidae family (79% and 63% of visits toP. spinosa andP. mahaleb, respectively). Results are compared with those for other rosaceous plants with fleshy fruits.     

Production and nitrogen responses of the African dwarf shrub Indigofera spinosa to defoliation and water limitation

Summary The dwarf shrub Indigofera spinosa Forsk. (Papilionacea), a native forage species of arid Northwest Kenya, was propogated from seed, grown in a controlled environment, and subjected to three treatments of defoliation and watering frequencies in a factorial experimental design. Biomass production and nitrogen accumulation in tissue components were measured to determine defoliation responses in a water-limited environment. We hypothesized that plants would maintain biomass and nitrogen flows despite removal of aboveground meristems and tissues by defoliation. Principal experimental results included a slight reduction (11%; P=0.08) of total biomass production by clipping ca. 1/3 or 2/3 of new leaves and stems and all apical meristems every month. Total aboveground production was not affected by clipping, while final root biomass was reduced 17% by the 2/3 clipping. The least water stressed plants were affected most negatively by defoliation, and the unclipped plants responded more negatively to greater water limitation. Plants achieved partial biomass compensation through alterations in shoot activity and continued allocation of photosynthate to roots. A smaller fraction of leaf production was directed to litter in clipped plants although clipping only removed the youngest tissues, suggesting that clipping increased leaf longevity. In turn, each leaf probably contributed a greater total quantity of photosynthate. Photosynthetic rates were also likely to have been increased by clipping water-stressed plants. In contrast to biomass, plants overcompensated for nitrogen lost to defoliation. Total nitrogen uptake by individual plants was stimulated by defoliation, as there was more total nitrogen in leaves and stems. Increased nitrogen uptake was achieved by clipping stimulation of total uptake per unit of root rather than of total root mass.     

Change in response of Rhopalosiphum padi spring migrants to the repellent winter host component methyl salicylate

Olfactometry showed that the response of spring migrants of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae), to the repellent winter host volatile methyl salicylate changes with age of the adult aphid. Between three and four days after becoming adult, and having left the winter host Prunus padus L., aphids lost their negative response to the chemical. The change in response was not associated with contact with a summer host, oats. In a settling choice bioassay, migrants avoided oats which had been exposed to volatile methyl salicylate. Aphids with removed antennal tips did not avoid the exposed plant, indicating that plant choice was influenced by cues from the plant surface. The results are discussed in relation to the use of methyl salicylate in integrated control.     

Genotype-specific response of a lycaenid herbivore to elevated carbon dioxide and phosphorus availability in calcareous grassland

Effects of elevated CO₂ and P availability on plant growth of the legume Lotus corniculatus and consequences for the butterfly larvae of Polyommatus icarus feeding on L. corniculatus were investigated in screen-aided CO₂ control chambers under natural conditions on a calcareous grassland in the Swiss Jura mountains. Elevated CO₂ conditions and P fertilisation increased the biomass production of L. corniculatus plants and affected the plant chemical composition. CO₂ enrichment increased the C/N ratio and sugar concentration and decreased the N and P concentrations. C- and N-based allelochemicals (cyanoglycosides, total polyphenols and condensed tannins) were only marginally affected by CO₂ enrichment. P fertilisation increased the specific leaf area and concentrations of water, N, sugar and P, while the C/N ratio and the concentration of total polyphenols decreased. Furthermore, P availability marginally enhanced the effect of elevated CO₂ on the total dry mass and sugar concentration while the opposite occurred for the total polyphenol concentration. The changes in food-plant chemistry as a result of P fertilisation positively affected larval mass gain and accelerated the development time of P. icarus. Only a marginal negative effect on larval mass gain was found for CO₂ enrichment. However, we found genotype-specific responses in the development time of P. icarus to elevated CO₂ conditions. Larvae originating from different mothers developed better either under elevated CO₂ or under ambient CO₂ but some did not react to CO₂ elevation. As far as we know this is the first finding of a genotype-specific response of an insect herbivore to elevated CO₂ which suggests genetic shifts in insect life history traits in response to elevated CO₂.     

The effects of Chilomonas on the life history traits of [-2pt] Daphnia longispina under semi-natural conditions and the implications for competition in the plankton

Assuming that heterotrophic flagellates (H.F.) can sustain cladoceran life cycles, particularly at periods of low food and high detritus conditions, the growth, reproduction and life span of Daphnia longispinawere studied under conditions of summer food limitation. They were fed both natural resources and natural food enriched with a culture of the colourless Chilomonas (ovoid cell, 8 × 25 m). Four H.F. morphotypes occurred in the natural water and the first experiments with Daphnia, showed that the cladoceran would most easily ingest those of 5 m–10 m, while the addition of Chilomonas severely depressed the H.F. of 2 m. The capability of this flagellate to ingest small H.F. was confirmed using fluorescent particles ranging from 0.94 to 3.95 m. As a consequence, Daphnia could control the abundance of H.F., but also compete with the largest morphotypes. To study the influence of the H.F. on the life span of Daphnia, the cladoceran was acclimated for two generations, before the start of the experiments. In semi-natural conditions, constant temperature, without predators and fed natural water, the summer daphnids achieved smaller sizes, produced fewer offspring and lived for a shorter time than when Chilomonas was added to their diet. Despite the addition of 560 g C l^-1, this was not sufficient to enhance the Daphnia reproduction to the level of the spring population fed natural water. These results clearly illustrate that the heterotrophic flagellates contributed significantly to improving the reproduction and survival of the daphnids. They emphasise the importance of the microbial loop as a link to larger consumers, particularly when unpalatable or nutritionally inadequate algae are dominant, which is often so in lakes during summer.     

Differences in environmental response between the sexes of the dioecious shrub Baccharis halimifolia (Compositae)

Summary Baccharis halimifolia (Compositae) is a dioecious shrub which grows on the upland fringe of tidal marshes along the Atlantic and Gulf Coasts of North America. We examined the responses of the two sexes to variation in nutrient and moisture availability plant density, and defoliation. By growing plants from seedlings to flowering adults under various combinations of soil type, fertilization rate and plant density, we were able to establish different rates of plant growth and mortality. Plants grown at high density and low nutrient and water supply grew the least, incurrent the most mortality and showed a male-biased sex ratio (73% male). At low density with abundant nutrients and water, plants grew more, survived well, flowered frequently, and were female-biased (75% female). Changes in sex ratio were probably the result of sex-related mortality rather than sexual lability of the seedlings. While changes in sex ratio occurred under experimental conditions in the green-house, no evidence for differences in habitat utilization between the sexes were found in the field and the sex ratio (59% female) did not vary across habitats. In the marsh habitats we sampled where water and nutrients were apparently available, there was no evidence for differential mortality between the sexes. When defoliated (75% of leaf tissue), both sexes showed similar reductions in reproductive effort (number of flower heads/shoot). Our results indicate that differences between the sexes of Baccharis in their response to environmental growing conditions is an important ecological factor associated with the separation of male and female function into separate individuals.     

Vegetative response of Arctostaphylos uva-ursi to experimental cutting and burning

Arctostaphylos uva-ursi uses vegetative resprouting to recover rapidly after disturbances. This study aims to widen knowledge of its regeneration response, so it was subjected to experimental cutting and burning. Fifteen pairs of small circular plots (50 cm diameter) were situated at random in an area where this species is abundant and forms homogeneous carpets with close to 100% cover. One plot of each pair was burned and the other one was cut. Initial biomass was estimated as dry weight from the cut plots. A 50 cm diameter circular sampling quadrat, divided into two concentric circles, was used in order to determine cover recovery and the way in which this occurred (predominantly by colonization from outside or uniformly over the whole surface). Initial recovery was very fast after both disturbances, exceeding 30% cover from the fourth month. Recovery of aboveground biomass was also similar on comparing both types of disturbance, but statistically significant differences with respect to initial values were detected.     

Functional response of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) to Aphis gossypii Glover (Homoptera: Aphididae) in the Laboratory

Stage specific functional response of Harmonia axyridis (Pallas) to varying densities of Aphis gossypii Glover was examined in a simplified cucumber leaf arena under laboratory conditions. All stages of H. axyridis were isolated individually for 24 h with different prey densities at 25 °C and a photoperiod of 16:8 (L:D) h. The number of prey consumed by the predator was checked at 3, 6, 12, and 24 h. All stages of H. axyridis showed a Type II functional response. Based on the random predator equation, estimated attack rates of H. axyridis at 24 h were 0.0037, 0.0442, 0.3590, 0.3228, and 0.1456, and estimated handling times were 4.1001, 2.4575, 0.7500, 0.2132, and 0.1708 h for the first, second, third, and fourth instars, and female adult, respectively.     

The ampullae and medusae of the calcareous hydrozoan Millepora complanata

The ampullae and medusae of the calcareous hydrozoan Millepora complanata Lamarck from Barbados were examined by transmission and electron microscopy. The sequence of development of the ampullae, before and after release of medusae, is reported. The medusae are described from live material and compared with medusae of other hydrozoans.     

Fungi associated with the southern pine beetle: avoidance of induced defense response in loblolly pine

Summary Loblolly pines (Pinus taeda) are rapidly killed by colonizing southern pine beetle (Dendroctonus frontalis). The female beetles carry two species of fungi (Ceratocystis minor var. barrasii and an unnamed basidiomycete) within a mycangium. The insects are also frequently associated with a blue-staining form of C. minor. These fungi are inoculated into the tree during colonization. The tree has an induced defensive response that involves resin soaking and necrosis of affected tissue isolating the invading organlsms. The blue-staining fungus stimulates formation of this response in the tree, but the two mycangial fungi do not. These results suggest that the beetles are closely associated with two highly pathogenic fungi that do not stimulate one of the critical components of tree defense.     

Synthetic oligonucleotide probes for detection of mercury-resistance genes in environmental freshwater microbial communities in response to pollutants

Mercury-resistance genes were detected byin situ hybridization using new synthetic oligonucleotide probes specific formerA andmerB genes according to the published sequences of the corresponding enzymes. These DNA probes were used for the detection of specific mercury-resistant microorganisms isolated from the Rhine River which had been polluted 3 years previously in 1986. Mercuric reductase and organomercurial lyase genes persist in the bacterial genome even after the disappearance of the pollutant but are absent in axenic amoebae. A total of 49 bacterial isolates showed DNA homologies with the³²P-labelled DNA probes and 15 free-living amoebae were selected due to their harboured symbiotic mercury-resistant bacteria.     

Short-term study of effects of fertilisation and cutting treatments on the vegetation dynamics of mountain heathlands in Spain

The influence of management and nutrient availability on the vegetation dynamics of heathlands characterised by Calluna vulgaris and Erica tetralix were studied in three mountain sites in Northern Spain. A total of 90 plots (1 m² each) received different combinations of cutting and twice the estimated background atmospheric deposition of nitrogen (56 kg ha⁻¹ yr⁻¹). One of the two dominant ericaceous species was selectively cut by hand at ground level and their regeneration compared in the presence or absence of the other. The results after 2 years showed significant effects of the fertiliser on the vegetation cover, mainly by favouring perennial herbaceous species. There were less noteworthy effects on the number of flowers and on the annual growth of the ericaceous species. It is concluded that, in the short term, increased nutrients alone, at twice the estimated current atmospheric deposition for the area, will not alter significantly the composition of the mountain heathlands. However, once the stands reach the mature phase, the capacity of the community to regenerate after a severe disturbance diminishes. A drastic impact, such as cutting may not result in re-growth of the same shrub species but in replacement by herbaceous species, which will also benefit from the increased nutrients.     

A Field Experiment to Assess the Transplant Success of Salt Marsh Plants into Tidal Wetlands

Field plots were used to assess the restoration potential of three salt marsh species, Juncus maritimus, Leptocarpus similis and Schoenoplectus pungens, within an established salt marsh near Christchurch, New Zealand. A split-block design was used to asses the effects of soil type, (soil from a proposed marsh construction site or estuarine mud from a natural salt marsh), species and plant source (commercial nursery stocks or natural marsh stock). In December, after 9 months, there was no mortality in L. similis and a significant increase in the biomass compared with J. maritimus. S. pungens failed to regenerate following seasonal die-back. Plant biomass was unaffected by soil type, despite occasional higher salinities recorded in the reclamation soil. Natural stocks had significantly higher biomass than nursery stocks (p < 0.01). These results suggest that both L. similis and J. maritimus are appropriate species for transplanting in the Canterbury region and that the soil from the proposed area is suitable for the restoration and construction of tidal wetlands. The success of the transplants could be enhanced by sourcing hardy stock and management regimes may be necessary to reduce salinity extremes and herbivory by rabbits.     

Dinoflagellate community analysis of a fish kill using denaturing gradient gel electrophoresis

A molecular method using the polymerase chain reaction (PCR) amplification of small subunit gene sequences (18S rDNA) and denaturing gradient gel electrophoresis (DGGE) was used to determine both the population complexity and species identification of organisms in harmful algal blooms. Eighteen laboratory cultures of dinoflagellates, including Akashiwo, Gymnodinium, Heterocapsa, Karenia, Karlodinium, Pfiesteria, and Pfiesteria-like species were analyzed using dinoflagellate-specific oligonucleotide primers and DGGE. The method is sensitive and able to determine the number of species in a sample, as well as the taxonomic identity of each species, and is particularly useful in detecting differences between species of the same genus, as well as differences between morphologically similar species. Using this method, each of eight Pfiesteria-like species was verified as being clonal isolates of Pfiesteria piscicida. The sensitivity of dinoflagellate DGGE is approximately 1000 cells/ml, which is 100-fold less sensitive than real-time PCR. However, the advantage of DGGE lies in its ability to analyze dinoflagellate community structure without needing to know what is there, while real-time PCR provides much higher sensitivity and detection levels, if probes exist for the species of interest, attributes that complement DGGE analysis. In a blinded test, dinoflagellate DGGE was used to analyze two environmental fish kill samples whose species composition had been previously determined by other analyses. DGGE correctly identified the dominant species in these samples as Karlodinium micrum and Heterocapsa rotundata, proving the efficacy of this method on environmental samples. Toxin analysis of a clonal isolate obtained from the fish kill samples confirmed the presence of KmTx2, corroborating the earlier genetic identification of toxic K. micrum in the fish kill water sample.     

Alien seedling recruitment as a response to altitude and soil disturbance in the mountain grasslands of central Argentina

Climate and disturbance are considered key factors in explaining plant invasion, mainly by their effect on alien seedling recruitment. We tested whether soil disturbance by digging and altitude, as a sub-set of climate, affected the seedling recruitment of two alien species (Cirsium vulgare and Melilotus alba) in the mountain grasslands of central Argentina. We performed a seed-addition factorial experiment with altitude as a fixed factor co-variable (6 levels), time since sowing (6 levels) as an autoregressive co-variable, and soil disturbance by digging (two levels) and seed addition (two levels) as fixed factors. Seeds of the studied species were sown in replicated undisturbed and disturbed soil plots, in grassland stands located every 200 m from 1200 to 2200 m a.s.l. The number of emerging seedlings at each plot was recorded during a period of 8 months, at intervals of 30–60 days. Seedlings of both alien species emerged at all the studied altitudes, but only the recruitment of C. vulgare increased linearly with altitude. Moreover, the time window of seedling recruitment for this species increased with altitude. Soil disturbance produced a significant decrease in overall seedling emergence of both species; however, an increase in emergence was observed for C. vulgare at an altitude over 2000 m a.s.l. Natural emergence inside control plots without seed addition was only observed for Cirsium vulgare, which indicates that this species was not seed limited. Our results show that altitude and the absence of disturbance do not restrict the recruitment of C. vulgare and M. alba in these natural mountain grasslands. Moreover, these alien species seem to be tolerant to and even favoured by conditions occurring at higher altitudes and in absence of micro-site soil disturbances in the Córdoba mountain grasslands.     

Influence of resource abundance on the structure of the insect community attracted to fermented tree sap

There has been little or no documentation of the insect community attracted to fermented tree sap, despite our familiarity with it. This study describes the influence of resource abundance (exudate quantity) on species richness, insect abundance, and diversity at the patch level in order to elucidate the mechanisms responsible for community structure. Resource abundance was positively correlated with species richness and insect abundance, negatively correlated with the equitability index (J), and not significantly correlated with diversity (Simpsons index of diversity; 1/D). Both correlation analyses and canonical correspondence analysis based on taxonomic categories indicated that responses to resource abundance were much greater in parasitoid wasps (Ichneumonoidea), drosophilid flies (Drosophilidae), and rove beetles (Staphylinidae). Field experiments showed that patches with more of the resource had greater species richness and greater hornet abundance. These results indicate that resource abundance is an important factor that affects community structure at the patch level, although it does not influence diversity directly, due to differences in the response to a resource across subgroups; drosophilid flies, the most abundant group that was heavily dependent on tree sap, make an especially large contribution to the change in J. Various factors influence the variation in the response to resource abundance, including population size, feeding habits, and resource utilization patterns (i.e. whether the species uses patches as habitat).     

Competitive effects of the invasive shrub,Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings

Invasive plants are often associated with reduced cover of native plants, but rarely has competition between invasives and natives been assessed experimentally. The shrub Lonicera maackii, native to northeastern Asia, has invaded forests and old fields in numerous parts of eastern North America, and is associated with reduced tree seedling density in Ohio forests. A field experiment was conducted to test the effects of established L. maackii on the survival and growth of transplanted native tree species. The experiment examined above-ground competition (by removing L. maackii shoots) and below-ground competition (by trenching around transplanted seedlings). The effects of above-ground competition with L. maackii were generally more important than below-ground competition, though both were detected. Shoot treatment was the key determinant for the survival of all species except P. serotina, whereas trenching only enhanced survival for A. saccharum caged and P. serotina, and only in the shoot removal treatment. For the surviving seedlings, L. maackii shoot removal increased growth of A. saccharum seedlings protected with cages, but actually reduced the growth of unprotected Q. rubra and A. saccharum seedlings, indicating that L. maackii shoots confer some protection from deer browsing. Significant interactions between root and shoot treatment on Q. rubra growth parameters, specifically greatest growth in the shoot present & trenched treatment, is attributed to protection from deer browsing combined with release from below-ground competition. Despite this protective function of L. maackii shoots, the overall effect of this invasive shrub is increased mortality of native tree seedlings, suggesting it impacts the natural regeneration of secondary forests.     

In vitro transcriptome analysis of porcine choroid plexus epithelial cells in response to Streptococcus suis: release of pro-inflammatory cytokines and chemokines

The Gram-positive zoonotic bacterium Streptococcus suis (S. suis) is responsible for a wide range of diseases including meningitis in pigs and humans. The blood-cerebrospinal fluid (CSF) barrier is constituted by the epithelial cells of the choroid plexus, which execute barrier function also after bacteria have entered the central nervous system (CNS). We show that the bacterial capsule, a major virulence factor, strongly attenuates adhesion of S. suis to the apical side of porcine choroid plexus epithelial cells (PCPEC). Oligonucleotide microarray analysis and quantitative PCR surprisingly demonstrated that adherent wild-type and capsule-deficient S. suis influenced expression of a pronounced similar pattern of genes in PCPEC. Investigation of purified capsular material provided no evidence for a significant role of the capsule. Enriched among the regulated genes were those involved in “inflammatory response”, “defense response” and “cytokine activity”. These comprised several cytokines and chemokines including the interleukins 6 and 8, which could be detected on protein level. We show that after infection with S. suis the choroid plexus contributes to the immune response by actively producing cytokines and chemokines. Other virulence factors than the bacterial capsule may be relevant in inducing a strong inflammatory response in the CNS during S. suis meningitis.