Responses to fertility and disturbance in a low-diversity grassland

We examined variation in species composition in a low-diversity, anthropogenic grassland in response to 11 years of nitrogen (N) manipulation and disturbance. The species-poor grassland (2–3 species/0.5 m²) represents a wide spread vegetation type (>10 million ha in North America) dominated by the introduced perennial grasses Bromus inermis and Agropyron cristatum. Four levels of N and three of soil disturbance were applied in all combinations to plots (5 × 15 m, N = 120) in a completely randomized design each year. Seeds or transplants of 47 species were added to ensure that dispersal was not a barrier to changes in species composition. After 11 years of treatment, all but the most disturbed plots continued to be dominated by B. inermis. The cover of the second-most abundant species, A. cristatum, decreased with disturbance but did not vary significantly with N. Despite the lack of changes in the identity of the dominant species, our environmental manipulations strongly influenced ecosystem characteristics. Added N increased soil available N, and decreased the cover of bare ground and light availability. Soil disturbance decreased aboveground biomass, and increased the cover of bare ground and light availability. Sawdust application, designed to decrease N availability, significantly reduced community biomass, and increased light availability and the cover of bare ground, but did not alter nutrient availability or species composition. The results highlight the difficulty of restoring diversity in species-poor, anthropogenic communities dominated by introduced species, and thus the importance of conserving remnants of diverse natural grasslands.     

The biology of Brachycentrus subnubilus Curtis (Trichoptera) in the River Frome,Dorset

Aspects of life-history, oviposition and microdistribution within beds of Ranunculus penicillatus var. calcareus (R. W. Butcher) C.D.K. Cook are considered. Brachycentrus subnubilus Curtis has one generation each year, with five larval instars. Larvae favour sites beneath the weedbeds for most of the year, migrating to more exposed areas in the spring to pupate. Pupation, emergence, oviposition and eclosion are completed in just over two months. Eggs are usually laid on submerged marginal vegetation but any semi-submerged object may be utilized. Larvae appear to disperse mainly as first instars; in this they are likely to be seriously affected by weedcutting activities. Initial development is rapid to fourth instar. Larvae overwinter as fifth instars. Sex ratios show a predominance of males.     

Ecological correlates of invasion by <Emphasis Type="Italic">Arundo donax</Emphasis> in three southern California riparian habitats

Arundo donax L. (Poaceae) is an aggressive invader in California’s riparian habitats. Field experiments were conducted to examine invader and site attributes important in early invasion. One hundred A. donax rhizomes were planted along five transects into each of three southern California riparian habitats. Pre-planting rhizome weight was recorded, along with site variables including percent bare ground, litter depth, PAR, soil moisture, soil temperature, incidence of herbivory, native canopy cover, and plant community richness and diversity. A. donax shoot emergence, survival time, and shoot height were recorded for approximately 10 months. The experiment was repeated over three years in different locations within each site. When years and sites were pooled to reveal large-scale patterns, A. donax performance was explained by rhizome weight, soil moisture, bare ground, soil temperature, and herbivory. When each site was considered singly, A. donax was positively correlated with different variables in each location. Species richness was correlated with A. donax performance in only one site. Our results indicate that A. donax establishment in riparian habitats is promoted by both vegetative reproduction and favorable abiotic environmental factors and relatively unaffected by the composition of the native community. The positive response of A. donax to disturbance (bare ground) and high resource availability (soil moisture), combined with a competitive perennial habit suggest that this species takes advantage of a competitive-ruderal life history. The ability of A. donax to respond to different conditions in each site combined with low genetic and phenotypic variation seen in other studies also suggests that a high degree of environmental tolerance contributes to invasion success.     

The role of exotic plants in the invasion of Seychelles by the polyphagous insect <Emphasis Type="Italic">Aleurodicus dispersus</Emphasis>: a phylogenetically controlled analysis

The accidental introduction of the spiralling whitefly, Aleurodicus dispersus Russell (Homoptera: Aleyrodidae) to Seychelles in late 2003 is exploited during early 2005 to study interactions between A. dispersus, native and exotic host plants and their associated arthropod fauna. The numbers of A. dispersus egg spirals and pupae, predator and herbivore taxa were recorded for eight related native/exotic pairs of host plants found on Mahé, the largest island in Seychelles. Our data revealed no significant difference in herbivore density (excluding A. dispersus) between related native and exotic plants, which suggests that the exotic plants do not benefit from ‘enemy release’. There were also no differences in predator density, or combined species richness between native and exotic plants. Together these data suggest that ‘biotic resistance’ to invasion is also unlikely. Despite the apparent lack of differences in community structure significantly fewer A. dispersus egg spirals and pupae were found on the native plants than on the exotic plants. Additional data on A. dispersus density were collected on Cousin Island, a managed nature reserve in which exotic plants are carefully controlled. Significantly higher densities of A. dispersus were observed on Mahé, where exotic plants are abundant, than on Cousin. These data suggest that the rapid invasion of Seychelles by A. dispersus may largely be due to the high proportion of plant species that are both exotic and hosts of A. dispersus; no support was found for either the ‘enemy release’ or the ‘biotic resistance’ hypotheses.     

Tomato-aphid-hoverfly: a tritrophic interaction incompatible for pest management

Trichome-based tomato resistance offers the potential to reduce pesticide use, but its compatibility with biological control remains poorly understood. We evaluated Episyrphus balteatus De Geer (Diptera, Syrphidae), an efficient aphidophagous predator, as a potential biological control agent of Myzus persicae Sulzer (Hemiptera, Aphididae) on trichome-bearing tomato cultivars. Episyrphus balteatus’ foraging and oviposition behavior, as well as larval mobility and aphid accessibility, were compared between two tomato cultivars (Lycopersicon esculentum Mill. ‘Moneymaker’ and ‘Roma’) and two other crop plants; broad bean (Vicia faba L.) and potato (Solanum tuberosum L.). Hoverfly adults landed and laid more eggs on broad beans than on three species of Solanaceae. Hoverfly larval movement was drastically reduced on tomato, and a high proportion of hoverfly larvae fell from the plant before reaching aphid prey. After quantifying trichome abundance on each of these four plants, we suggest that proprieties of the plant surface, specifically trichomes, are a key factor contributing to reduced efficacy of E. balteatus as a biological agent for aphid control on tomatoes. Handling editor: Stanislaw Gorb     

Patterns of host ant use by sympatric populations of <Emphasis Type="Italic">Maculinea alcon</Emphasis> and <Emphasis Type="Italic">M. ‘rebeli’</Emphasis> in the Carpathian Basin

Maculinea butterflies show social parasitism via obligatory myrmecophily as their larvae are adopted and raised to pupation by Myrmica ants. Suitable hosts differ for different Maculinea species, and host ant specificity can further differ at the population-level. Although early studies suggested single ant species as main hosts for each Maculinea species, it has recently become clear that their host ant specificity is more complex. Maculinea alcon and Maculinea ‘rebeli’ have variously been separated according to adult and larval morphology, phenology, and their use of different ecosystems, including host plant and host ant species. However, recent genetic evidence has questioned their separation as good species. Here we compare the use of host ants by M. alcon and M. ‘rebeli’ at the regional scale in NE-Hungary and Transylvania (Romania), where molecular studies have found no species-level separation between the two forms. We opened 778 nests of Myrmica ants and searched for Maculinea specimens (larvae, pupae and exuviae) shortly before imago emergence from the nest in seven M. alcon sites, six M. ‘rebeli’- sites and one site where both M. alcon and M. ‘rebeli’ are syntopic. In all, Maculinea caterpillars were found in the nests of seven different ant species (M. alcon was recorded mainly with Myrmica scabrinodis and occasionally with M. salina and M. vandeli; M. ‘rebeli’ used mainly M. scabrinodis, M. sabuleti and M. schencki and occasionally M. lonae and M. specioides). Myrmica scabrinodis was found to be a general host of both M. alcon and M. ‘rebeli’, which is the first record for a common host ant of these two closely related butterflies within the same region. However there were also differences in host ant use patterns between the sites occupied by the two Maculinea taxa, which reflect differences in Myrmica communities between the two types of habitat. Possible explanations for the similar but not identical host use patterns of M. alcon and M. ‘rebeli’, and their relevance for the question of whether they are separate species are discussed. Received 27 November 2007; revised 28 May 2008; accepted 11 June 2008.     

Effects of ants on plant diversity in semi-natural grasslands

Ants (L. niger and L. flavus) build conspicuous mounds that are covered with vegetation. The aim of this study was to investigate whether the vegetation on ant mounds in semi-natural grasslands differed from that around the mounds. Another aim was to investigate whether the changes in the vegetation on ant mounds were influenced by grazing management or by habitat characteristics, semi-dry versus moist. Here, the total number of plant species and total plant cover were lower on ant mounds than in patches off-mound. The plant cover of perennials that form rosettes was twice as high on mounds inhabited by L. niger than on those inhabited by L. flavus. Only a few plant species were restricted to either ant mounds or adjacent field and the effects of ants on the plant diversity in semi-natural grasslands seemed to be low. Grazing management did not affect the differences in the vegetation on ant mounds and in equal-sized patches off-mound, whereas habitat characteristics affected ant-induced changes in vegetation cover of some plant species.     

Influence of food hoarding behavior on the over-winter survival of pikas in strongly seasonal environments

Food hoarding is a behavioral adaptation of some herbivores to manage food availability through time and space. In strongly seasonal environments, where summer growing seasons are short relative to winter, an earlier start to hoarding should increase the amount of vegetation stored for winter and improve subsequent survival. We examined hoarding behavior (‘haying’) and its impact on survival for a small alpine lagomorph, the collared pika (Ochotona collaris) in Yukon, Canada. We used a combination of video surveillance, haypile measurements, and survival data from marked individuals of known age and sex. Annual haypile initiation was strongly influenced by age and year. Adult pikas began haying an average of 16 days earlier in 2004 relative to 2005, whereas young of the year (juveniles) did not vary in the timing of haypile initiation. The mean haying rate per hour increased monthly from 3.7 ± 0.7 trips in June to 6.6 ± 0.8 trips in August. Simulation analysis estimated the median haypile mass (dry weight) by mid-September to be 5.5 kg. At least 75% of simulated haypiles had a minimum of 90 days (3 months) of food reserves, and 50% of simulated haypiles had a minimum of 177 days (5.9 months) of food reserves by mid-September, supporting the hypothesis that haypiles serve as the primary source of food during winter. Survival was greatest for pikas in 2005 when they began haying prior to 31 July, but the benefits of earlier accumulation of vegetation on survival also varied between years. The implications of earlier spring snowmelt are discussed with respect to pika foraging and overwinter survival.     

Does Prunus serotina act as an aggressive invader in areas with a low propagule pressure?

Since most studies on Prunus serotina in Western Europe focused on heavily invaded areas, we wondered whether P. serotina also acts as an aggressive invader in areas with a low propagule pressure. Based on long-term data for the Liedekerke forest reserve, we found that connectivity to seed sources and light availability were the major drivers of P. serotina presence: long-distance dispersal events and ‘windows of opportunity’ seem to direct P. serotina colonization. In the studied forest, P. serotina could not be considered an aggressive invader since its spread slowed down rather quickly and did not hamper the establishment of native tree species. Furthermore, understory P. serotina showed low growth and seed production, while the high Rubus cover hampered germination and establishment. Nonetheless, calamities opening up the canopy layer in the few areas with high P. serotina sapling density might alter the course of the invasion process.     

Response of ants and spiders to prescribed fire in oak woodlands of California

Conservation managers of oak woodlands have been reintroducing fire both as an ecological process per se and to assist in restoring native plant communities. To increase our understanding of the impacts of reintroduced fire on ground-dwelling invertebrates we examined the response of ants and spiders to a late season (autumn) prescribed fire conducted in a blue oak (Quercus douglasii) woodland ecosystem in northern California. Twelve 100 m × 100 m plots were established, six plots received a burn treatment and the remaining six plots were unburned controls. Ants and spiders were sampled using pitfall traps left open continuously and collected approximately every 32 days. Sampling was conducted over a year, consisting of four pre-burn and nine post-burn collections. Abundance was analyzed using a repeated measures ANOVA, which showed seed-harvester ants decreased significantly in the two months following the fire. Total spider abundance also showed a significant decrease in two months, although this did not occur immediately after the burn. One spider hunting guild, the ‘diurnal ambush’ group (Thomisidae) remained suppressed for up to nine months. Correspondence analysis measures of ant species abundance with environmental and vegetation variables (percent rock, bare ground, plant species richness and height of herbaceous vegetation) were higher than expected by chance, which assists in explaining some of the responses. Findings from this study revealed that the reintroduction of autumn burns has modest and short-term effect on the invertebrates sampled, suggesting that late season fires are compatible with other conservation goals for oak woodland ecosystems.     

<Emphasis Type="Italic">Fopius arisanus</Emphasis> oviposition in four <Emphasis Type="Italic">Anastrepha</Emphasis> fruit fly species of economic importance in Mexico

We studied the oviposition performance of Fopius arisanus (Sonan) (Hymenoptera: Braconidae) attacking eggs of four fruit flies of the genus Anastrepha Schiner (Diptera: Tephritidae) under laboratory conditions. The complete process of oviposition on an individual egg of Anastrepha ludens (Loew) lasts in average 85.4 ± 2.9 s, including a tremor (25.8 ± 1.03 s) observed in the middle of this process related to the egg’s descent. The average parasitism of A. ludens egg was 60.9 ± 7.5%, with only 1.2% of superparasitized eggs. During individual acts of oviposition, we noted that F. arisanus possesses a highly flexible ovipositor that curves easily as it searches for additional suitable eggs, which may be of particular benefit when a female finds large clutches of eggs. The individual oviposition of F. arisanus in host fruits attacked by Anastrepha spp. varies with the egg clutch size of each fruit fly species: A. serpentina laid the biggest egg clutches (21.3 ± 1.4), followed by A. ludens (14.2 ± 0.9), and A. striata (1.0 ± 0.0) (=A. obliqua). The time spent by F. arisanus in individual ovipositions was parallel to these findings, reinforcing the idea that F. arisanus attacks several eggs in each individual insertion of its ovipositor. Neither formal oviposition acts, nor adult emergences of F. arisanus were registered in A. obliqua. We discuss the potential of F. arisanus as natural enemy of fruit flies of the genus Anastrepha, and explore the eventual developing of its mass rearing. Handling Editor: Torsten Meiners.     

The role of below-ground competition during early stages of secondary succession: the case of 3-year-old Scots pine (Pinus sylvestris L.) seedlings in an abandoned grassland

In abandoned or extensively managed grasslands, the mechanisms involved in pioneer tree species success are not fully explained. Resource competition among plants and microclimate modifications have been emphasised as possible mechanisms to explain variation of survivorship and growth. In this study, we evaluated a number of mechanisms that may lead to successful survival and growth of seedlings of a pioneer tree species (Pinus sylvestris) in a grass-dominated grassland. Three-year-old Scots pines were planted in an extensively managed grassland of the French Massif Central and for 2 years were either maintained in bare soil or subjected to aerial and below-ground interactions induced by grass vegetation. Soil temperatures were slightly higher in bare soil than under the grass vegetation, but not to an extent explaining pine growth differences. The tall grass canopy reduced light transmission by 77% at ground level and by 20% in the upper part of Scots pine seedlings. Grass vegetation presence also significantly decreased soil volumetric water content (Hv) and soil nitrate in spring and in summer. In these conditions, the average tree height was reduced by 5% compared to trees grown in bare soil, and plant biomass was reduced by 85%. Scots pine intrinsic water-use efficiency (A/g), measured by leaf gas-exchange, increased when Hv decreased owing to a rapid decline of stomatal conductance (g). This result was also confirmed by δ ¹³C analyses of needles. A summer ¹⁵N labelling of seedlings and grass vegetation confirmed the higher NO₃ capture capacity of grass vegetation in comparison with Scots pine seedlings. Our results provide evidence that the seedlings' success was linked to tolerance of below-ground resource depletion (particularly water) induced by grass vegetation based on morphological and physiological plasticity as well as to resource conservation.     

High-efficiency <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of citrus via sonication and vacuum infiltration

An improved method for the Agrobacterium infiltration of epicotyl segments of ‘Pineapple’ sweet orange [Citrus sinensis (L.) Osbeck] and ‘Swingle’ citrumelo [Citrus paradisi Macf. X Poncirus trifoliata (L.) Raf.] was developed in order to increase transformation frequency. Sonication-assisted Agrobacterium-mediated transformation (SAAT), vacuum infiltration, and a combination of the two procedures were compared with conventional Agrobacterium-mediated inoculation method (‘dipping’ method). It was observed that the morphogenic potential of the epicotyl segments decreased as the duration of SAAT and vacuum treatments increased. Transient GUS expression was not affected by the different SAAT treatments, but it was significantly enhanced by the vacuum infiltration treatments. The highest transformation efficiencies were obtained when the explants were subjected to a combination of SAAT for 2 s followed by 10 min of vacuum infiltration. PCR and Southern blot analysis of the uidA gene were used to confirm the integration of the transgenes. The transformation frequencies achieved in this study (8.4% for ‘Pineapple’ sweet orange and 11.2% for ‘Swingle’ citrumelo) are the highest ones reported for both cultivars.     

A caveat in mouse genetic engineering: ectopic gene targeting in ES cells by bidirectional extension of the homology arms of a gene replacement vector carrying human PARP-1

Here we report an approach to generate a knock-in mouse model using an ‘ends-out’ gene replacement vector to substitute the murine Parp-1 (mParp-1) coding sequence (32 kb) with its human orthologous sequence (46 kb). Unexpectedly, examination of mutant ES cell clones and mice revealed that site-specific homologous recombination was mimicked in three independently generated ES cell clones by bidirectional extension of the vector homology arms using the endogenous mParp-1-flanking sequences as templates. This was followed by adjacent integration of the targeting vector, thus leaving the endogenous mParp-1 locus functional. A related phenomenon termed ‘ectopic gene targeting’ has so far only been described for ‘ends-in’ integration-type vectors in non-ES cell gene targeting. We provide reliable techniques to detect such ectopic gene targeting which represents an unexpected caveat in mouse genetic engineering that should be considered in the design and validation strategy of future gene knock-in approaches. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Rust mite resistance in apple assessed by quantitative trait loci analysis

The aim of this study was to assess the genetic basis of rust mite (Aculus schlechtendali) resistance in apple (Malus × domestica). A. schlechtendali infestation of apple trees has increased as a consequence of reduced side effects of modern fungicides on rust mites. An analysis of quantitative trait loci (QTLs) was carried out using linkage map data available for F₁ progeny plants of the cultivars ‘Fiesta’ × ‘Discovery’. Apple trees representing 160 different genotypes were surveyed for rust mite infestation, each at three different sites in two consecutive years. The distribution of rust mites on the individual apple genotypes was aggregated and significantly affected by apple genotype and site. We identified two QTLs for A. schlechtendali resistance on linkage group 7 of ‘Fiesta’. The AFLP marker E35M42-0146 (20.2 cM) and the RAPD marker AE10-400 (45.8 cM) were closest positioned to the QTLs and explained between 11.0% and 16.6% of the phenotypic variability. Additionally, putative QTLs on the ‘Discovery’ chromosomes 4, 5 and 8 were detected. The SSR marker Hi03a10 identified to be associated to one of the QTLs (AFLP marker E35M42-0146) was traced back in the ‘Fiesta’ pedigree to the apple cultivar ‘Wagener’. This marker may facilitate the breeding of resistant apple cultivars by marker assisted selection. Furthermore, the genetic background of rust mite resistance in existing cultivars can be evaluated by testing them for the identified SSR marker. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Intraspecific nestmate recognition in two parabiotic ant species: acquired recognition cues and low inter-colony discrimination

Parabiotic ants—ants that share their nest with another ant species—need to tolerate not only conspecific nestmates, but also nestmates of a foreign species. The parabiotic ants Camponotus rufifemur and Crematogaster modiglianii display high interspecific tolerance, which exceeds their respective partner colony and extends to alien colonies of the partner species. The tolerance appears to be related to unusual cuticular substances in both species. Both species possess hydrocarbons of unusually high chain lengths. In addition, Cr. modiglianii carries high quantities of hereto unknown compounds on its cuticle. These unusual features of the cuticular profiles may affect nestmate recognition within both respective species as well. In the present study, we therefore examined inter-colony discrimination within the two parabiotic species in relation to chemical differentiation. Cr. modiglianii was highly aggressive against workers from alien conspecific colonies in experimental confrontations. In spite of high inter-colony variation in the unknown compounds, however, Cr. modiglianii failed to differentiate between intracolonial and allocolonial unknown compounds. Instead, the cuticular hydrocarbons functioned as recognition cues despite low variation across colonies. Moreover, inter-colony aggression within Cr. modiglianii was significantly influenced by the presence of two methylbranched alkenes acquired from its Ca. rufifemur partner. Ca. rufifemur occurs in two varieties (‘red’ and ‘black’) with almost no overlap in their cuticular hydrocarbons. Workers of this species showed low aggression against conspecifics from foreign colonies of the same variety, but attacked workers from the respective other variety. The low inter-colony discrimination within a variety may be related to low chemical differentiation between the colonies. Ca. rufifemur majors elicited significantly more inter-colony aggression than medium-sized workers. This may be explained by the density of recognition cues: majors carried significantly higher quantities of cuticular hydrocarbons per body surface.     

Parasitism ofLeptinotarsa decemlineata [Coleoptera: Chrysomelidae] byEdovum puttleri [Hymenoptera: Eulophidae] in different cultivars of eggplant

Experiments were conducted to quantify parasitism of Colorado potato beetle,Leptinotarsa decemlineata (Say), by the egg parasitoid,Edovum puttleri Grissell, on 3 different cultivars of eggplant,Solanum melongena L. Levels of parasitism were higher (P<0.05) on ‘Black Pride’ than on other cultivars. The percentage of egg masses that were parasitized was 1.2-fold higher (P<0.05) on ‘Black Pride’ than on ‘Harris Special’ and ‘White’. The number of eggs per mass that were parasitized was 1.3- and 1.4- fold greater (P<0.05) on ‘Black Pride’ than on ‘Harris Special’ and ‘White’, respectively. The percentage of eggs that were parasitized per mass and percentage of emerged adult parasitoids did not differ (P>0.05) among cultivars; between 2.1- to 2.6- fold more females than males emerged from eggs on all cultivars during the growing season.Edovum puttleri suppressed the 2nd generation ofL. decemlineata on ‘Black Pride’ and ‘Harris Special’, but did not suppress populations on ‘White’.      

Prospects for Bonobo Insectivory: Lui Kotal, Democratic Republic of Congo

Chimpanzees (Pan troglodytes) are well-known to eat invertebrates, especially social insects, across Africa, but allopatric bonobos (P. paniscus) are not. Bonobo insectivory is sparsely documented and apparently sporadic. However, the availability to bonobos of social insect prey and raw materials with which to make tools to exploit them is unknown. Here, we test a set of hypotheses that relates to questions of presence, abundance, density, and distribution of taxa that Pan consume and of vegetation suitable for making extractive foraging tools. We worked at Lui Kotal, Democratic Republic of Congo, where unprovisioned bonobos live in intact forest, far from villages. We collected insect and fecal specimens, transected for prey and assessed raw materials, and monitored mounds of Macrotermes. All but 1 of the major taxa of relevant termites, ants, and (stinging) honey bees were present. The 3 main taxa of insects that chimpanzees elsewhere eat —Macrotermes (fungus-growing termites), Dorylus (Anomma; army or driver ants), and Apis (honey bees)— were abundant and widespread, and usually at densities exceeding those at well-known chimpanzee study-sites. Similarly, woody and nonwoody vegetation suitable for making fishing probes was common at mounds of Macrotermes. There is no obvious ecological reason why bonobos should not use elementary technology in extractive foraging, e.g., termite-fish, ant-fish, ant-dip, honey-dip, to obtain social insects.