Does the differential seedling mortality caused by slugs alter the foliar traits and subsequent susceptibility of hybrid willows to a generalist herbivore?

Abstract 1. Many Salicaceae species naturally form hybrid swarms with parental and hybrid taxa that differ in secondary chemical profile and in resistance to herbivores. Theoretically, the differential mortality in the seedling stage can lead to changes in trait expression and alter subsequent interactions between plants and herbivores. This study examines whether herbivory by the generalist slug Arion subfuscus, which causes extensive mortality in young willow seedlings, causes shifts in (a) the foliar chemistry of F2 willow hybrids (Salix sericea and Salix eriocephala), and (b) the subsequent susceptibility to Japanese Beetles, Popillia japonica. 2. In 2001, two populations of F2 seedlings were generated: those that survived slug herbivory (80–90% of seedlings placed in the field were killed by the slugs) were designated as S-plants, whereas C-plants (controls) experienced no mortality. 3. Common garden experiments with cuttings from these populations, in 2001 and 2002, revealed extensive variation in the phenolic chemistry of F2 hybrids, but revealed no significant difference between S- and C-plants, although the levels of foliar nutrients, proteins and nitrogen tended to be higher in S-plants. 4. Concentrations of salicortin and 2′-cinnamoylsalicortin explained 55 and 38% of the the variation in leaf damage caused by Japanese beetles, and secondary chemistry was highly correlated within replicate clones (salicortin R²= 0.85, 2-cinnamoylsalicortin R²= 0.77, condensed tannins R²= 0.68). 5. Interestingly, Japanese beetle damage and condensed tannins were positively correlated within the S-plants, but not in the C-plants, suggesting that slugs had selected for plants with a positive relationship between tannins and P. japonica damage. This is unlikely to be a consequence of a preference for tannins, but is suggested to be related to the elevated nutrient levels in the S-plants, perhaps in combination with the complex-binding properties of tannins. 6. The damage was highly correlated within replicate clones and a model choice analysis suggested that Japanese beetle damage may be explained by four factors: concentrations of salicortin, condensed tannins, and nitrogen, as well as the specific leaf area (thick leaves were damaged less).     

Effects of insect herbivory on induced chemical defences and compensation during early plant development in Penstemon virgatus

Background and Aims

The lack of studies assessing the simultaneous expression of tolerance and resistance traits during seedling development and overall seedling defences as compared with adult plants, in general, constitutes a significant research need that can greatly improve our understanding of overall investment in defences during plant ontogeny.

Methods

Using two seedling and two juvenile stages of the perennial herb Penstemon virgatus (Plantaginaceae) evaluations were made of (a) patterns of investment in constitutive chemical defences [i.e. iridoid glycosides (IGs)], and (b) simultaneous variation in the short-term ability of seedling and juvenile stages to induce resistance traits, measured as induced chemical defences, or tolerance traits, measured as compensatory re-growth following moderate levels of damage by a specialist insect herbivore.

Key Results

Plants were highly defended during most of their transition from seedling to early juvenile stages, reaching a constant approx. 20 % dry weight total IGs. Furthermore, following 30 % above-ground tissue damage, seedlings and juvenile stages were equally able to induce resistance, by raising their IG concentration by approx. 8 %, whereas compensatory re-growth was only achieved at young juvenile but not seedling stages.

Conclusions

Two major trends emerged from this study: (1) in contrast to expected and previously observed trends, in this perennial plant species, seedlings seem to be one of the most well-defended stages as compared with adult ones; (2) high levels of constitutive defences did not limit the ability of young developmental stages to induce resistance following damage, although this response may come with a cost (i.e. decreased compensation) in young seedling stages. Hence, as has been previously demonstrated in few other systems, these results points towards an indirect evidence for a trade-off between tolerance and resistance traits at some, but not all, developmental stages; making them often difficult to detect.     

Larval competition alters susceptibility of adult Aedes mosquitoes to dengue infection

Dengue, the most important human arboviral disease, is transmitted primarily by Aedes aegypti and, to a lesser extent, by Aedes albopictus. The current distributions of these invasive species overlap and are affected by interspecific larval competition in their container habitats. Here we report that competition also enhances dengue infection and dissemination rates in one of these two vector species. We determined the effects of competition on adult A. aegypti and A. albopictus, comparing their susceptibility to infection with a Southeast Asian strain of dengue-2 virus. High levels of intra- or interspecific competition among larvae enhanced the susceptibility of A. albopictus to dengue virus infection and potential for transmission, as indicated by disseminated infections. Doubling the number of competing larvae (A. albopictus or A. aegypti), led to a significant (more than 60%) increase in the proportion of A. albopictus with disseminated dengue-2 infection. Competition-enhanced vector competence appears to result from a reduction in 'barriers' (morphological or physiological) to virus infection and dissemination and may contribute to the importance of A. albopictus in dengue transmission. Similar results for other unrelated arboviruses suggest that larval competition, common in mosquitoes, should be considered in estimates of vector competence for pathogens that infect humans.     

Copper and herbivory lead to priming and synergism in phytohormones and plant volatiles in the absence of salicylate-jasmonate antagonism

Abiotic stress factors can interfere with the emission of herbivore-induced plant volatile organic compounds (VOCs) and thus disrupt chemical communication channels between plants and other organisms. We investigated whether copper (Cu) stress alone or in conjunction with insect damage modifies the kinetics of (1) VOCs, (2) the VOC-inducing phytohormone jasmonic acid (JA) and (3) its putative antagonist salicylic acid (SA). Hydroponically grown Zea mays exposed to 10 and 80 µM of Cu showed no increases in JA or VOC levels in the absence of herbivory. However when challenged by herbivores, Cu (80 µM) caused ROS generation in root tissues and primed for increased JA accumulation and VOC emission in leaves. SA synthesis was equally primed but higher concentrations were also apparent before insects started feeding. In contrast, plants grown at 10 µM Cu did not differ from controls. These results show that abiotic and biotic stresses result in concentration-dependent, non-additive defense responses. Further support is given to the notion that JA-SA antagonism is absent in Z. mays.     

Interactive effects of plant-available soil silicon and herbivory on competition between two grass species

Background and Aims

The herbivore defence system of true grasses (Poaceae) is predominantly based on silicon that is taken up from the soil and deposited in the leaves in the form of abrasive phytoliths. Silicon uptake mechanisms can be both passive and active, with the latter suggesting that there is an energetic cost to silicon uptake. This study assessed the effects of plant-available soil silicon and herbivory on the competitive interactions between the grasses Poa annua, a species that has previously been reported to accumulate only small amounts of silicon, and Lolium perenne, a high silicon accumulator.

Methods

Plants were grown in mono- and mixed cultures under greenhouse conditions. Plant-available soil silicon levels were manipulated by adding silicon to the soil in the form of sodium silicate. Subsets of mixed culture pots were exposed to above-ground herbivory by desert locusts (Schistocerca gregaria).

Key Results

In the absence of herbivory, silicon addition increased biomass of P. annua but decreased biomass of L. perenne. Silicon addition increased foliar silicon concentrations of both grass species >4-fold. Under low soil-silicon availability the herbivores removed more leaf biomass from L. perenne than from P. annua, whereas under high silicon availability the reverse was true. Consequently, herbivory shifted the competitive balance between the two grass species, with the outcome depending on the availability of soil silicon.

Conclusions

It is concluded that a complex interplay between herbivore abundance, growth–defence trade-offs and the availability of soil silicon in the grasses'' local environment affects the outcome of inter-specific competition, and so has the potential to impact on plant community structure.     

Allocation of biomass and photoassimilates in juvenile plants of six Patagonian species in response to five water supply regimes

Background and Aims

The growth–differentiation balance hypothesis (GDBH) states that there is a physiological trade-off between growth and secondary metabolism and predicts a parabolic effect of resource availability (such as water or nutrients) on secondary metabolite production. To test this hypothesis, the response of six Patagonian Monte species (Jarava speciosa, Grindelia chiloensis, Prosopis alpataco, Bougainvillea spinosa, Chuquiraga erinacea and Larrea divaricata) were investigated in terms of total biomass and resource allocation patterns in response to a water gradient.

Methods

One-month-old seedlings were subjected to five water supply regimes (expressed as percentage dry soil weight: 13 %, 11 %, 9 %, 7 % or 5 % – field water capacity being 15 %). After 150 d, plants were harvested, oven-dried and partitioned into root, stem and leaf. Allometric analysis was used to correct for size differences in dry matter partitioning. Determinations of total phenolics (TP), condensed tannins (CT), nitrogen (N) and total non-structural carbohydrates (TNC) concentrations were done on each fraction. Based on concentrations and biomass data, contents of TP and CT were estimated for whole plants, and graphical vector analysis was applied to interpret drought effect.

Key Results

Four species (J. speciosa, G. chiloensis, P. alpataco and B. spinosa) showed a decrease in total biomass in the 5 % water supply regime. Differences in dry matter partitioning among treatments were mainly due to size variation. Concentrations of TP, CT, N and TNC varied little and the effect of drought on contents of TP and CT was not adequately predicted by the GDBH, except for G. chiloensis.

Conclusions

Water stress affected growth-related processes (i.e. reduced total biomass) rather than defence-related secondary metabolism or allocation to different organs in juvenile plants. Therefore, the results suggest that application of the GDBH to plants experiencing drought-stress should be done with caution, at least for Patagonian Monte species.     

Varying responses of insect herbivores to altered plant chemistry under organic and conventional treatments

The hypothesis that plants supplied with organic fertilizers are better defended against insect herbivores than those supplied with synthetic fertilizers was tested over two field seasons. Organic and synthetic fertilizer treatments at two nitrogen concentrations were supplied to Brassica plants, and their effects on the abundance of herbivore species and plant chemistry were assessed. The organic treatments also differed in fertilizer type: a green manure was used for the low-nitrogen treatment, while the high-nitrogen treatment contained green and animal manures. Two aphid species showed different responses to fertilizers: the Brassica specialist Brevicoryne brassicae was more abundant on organically fertilized plants, while the generalist Myzus persicae had higher populations on synthetically fertilized plants. The diamondback moth Plutella xylostella (a crucifer specialist) was more abundant on synthetically fertilized plants and preferred to oviposit on these plants. Glucosinolate concentrations were up to three times greater on plants grown in the organic treatments, while foliar nitrogen was maximized on plants under the higher of the synthetic fertilizer treatments. The varying response of herbivore species to these strong differences in plant chemistry demonstrates that hypotheses on defence in organically grown crops have over-simplified the response of phytophagous insects.     

Environmental influences on growth and defence responses of the invasive shrub,Lonicera maackii,to simulated and real herbivory in the juvenile stage

Background and Aims

Tolerance and defence against herbivory are among the many mechanisms attributed to the success of invasive plants in their novel ranges. Because tolerance and defence against herbivory differ with the ontogeny of a plant, the effects of herbivore damage on plant fitness vary with ontogenetic stage and are compounded throughout a plant''s lifetime. Environmental stresses such as light and nutrient limitations can further influence the response of the plant. Much is known about the response of plants in the seedling and reproductive adult stages, but less attention has been given to the pre-reproductive juvenile stage.

Methods

Juvenile plants of the North American invasive Lonicera maackii were exposed to simulated herbivory under high and low light and nitrogen availability and growth, allocation patterns and foliar defensive chemistry were measured. In a second experiment, complete nutrient availability and damage type (generalist caterpillar or simulated) were manipulated.

Key Results

Juvenile plants receiving 50 % defoliation had lower total biomass and a higher root^:^shoot ratio than controls for all treatment combinations except low nitrogen/low light. Low light and defoliation increased root^:^shoot ratio. Light, fertilization and defoliation had little impact on foliar defensive chemistry. In the second experiment, there was a reduction in total biomass when caterpillar damage was applied. The root^:^shoot ratio increased under low soil fertility and was not affected by defoliation. Stem-diameter growth rates and specific leaf area did not vary by damage type or fertilization. Foliar protein increased through time, and more strongly in defoliated plants than in controls, while peroxidase activity and total flavonoids decreased with time. Overall, resource limitations were more influential than damage in the growth of juvenile L. maackii plants.

Conclusions

The findings illustrate that even when resources are limited, the tolerance and defence against herbivory of a woody invasive plant in the juvenile stage may contribute to the establishment and persistence of some species in a variety of habitats.     

Influence of inoculation with plant growth promoting rhizobacteria (PGPR) on tomato plant growth and nematode reproduction under greenhouse conditions

Numerous species of soil bacteria which flourish in the rhizosphere of plants or around plant tissues stimulate plant growth and reduce nematode population by antagonistic behavior. These bacteria are collectively known as PGPR (plant growth promoting rhizobacteria). The effects of six isolates of PGPR Pseudomonas putida, Pseudomonas fluorescens, Serratia marcescens, Bacillus amyloliquefaciens, Bacillus subtilis and Bacillus cereus, were studied on tomato plant growth and root knot nematode reproduction after 45 days from nematode infection. The highest number of shoot dry weight/g (43.00 g) was detected in the plant treated with S. marcescens; then P. putida (34.33 g), B. amyloliquefaciens (31.66 g), P. fluorescens (30.0 g), B. subtilis (29.0 g), B. cereus (27.0 g) and nematode alone (untreated) 20 g/plant. While the highest number of plant height was observed when plant was treated with S. marcescens, P. fluorescens, P. putida, B. amyloliquefaciens and P. putida 52.66, 50.66, 48 and 48 cm respectively. No significant differences were seen between previous treatments but only had significant differences compared with untreated plant. The highest number of fruit/plant was observed when plants were treated with S. marcescens (10.66), then B. amyloliquefaciens (8.66), P. putida (8), P. fluorescens (8) and B. cereus (7.66). No significant differences between the last 4 treatments, but all had significant differences compared with untreated plants. The highest weight of plant yield (g) was observed with S. marcescens (319.6 g/plant) and the lowest weight of plant yield was observed in plants treated with nematode alone (untreated). On the other hand, the lowest numbers of J₂/10 g of soil (78), galls/root, (24.33) galls/root, egg masses/root (12.66) and egg/egg masses were observed in the plants treated with S. marcescens.     

Below-ground herbivory limits induction of extrafloral nectar by above-ground herbivores

Background and Aims Many plants produce extrafloral nectar (EFN), and increase production following above-ground herbivory, presumably to attract natural enemies of the herbivores. Below-ground herbivores, alone or in combination with those above ground, may also alter EFN production depending on the specificity of this defence response and the interactions among herbivores mediated through plant defences. To date, however, a lack of manipulative experiments investigating EFN production induced by above- and below-ground herbivory has limited our understanding of how below-ground herbivory mediates indirect plant defences to affect above-ground herbivores and their natural enemies.Methods In a greenhouse experiment, seedlings of tallow tree (Triadica sebifera) were subjected to herbivory by a specialist flea beetle (Bikasha collaris) that naturally co-occurs as foliage-feeding adults and root-feeding larvae. Seedlings were subjected to above-ground adults and/or below-ground larvae herbivory, and EFN production was monitored.Key Results Above- and/or below-ground herbivory significantly increased the percentage of leaves with active nectaries, the volume of EFN and the mass of soluble solids within the nectar. Simultaneous above- and below-ground herbivory induced a higher volume of EFN and mass of soluble solids than below-ground herbivory alone, but highest EFN production was induced by above-ground herbivory when below-ground herbivores were absent.Conclusions The induction of EFN production by below-ground damage suggests that systemic induction underlies some of the EFN response. The strong induction by above-ground herbivory in the absence of below-ground herbivory points to specific induction based on above- and below-ground signals that may be adaptive for this above-ground indirect defence.     

Genetic analysis of a wild-caught hybrid between non-sister Heliconius butterfly species

Interspecific hybridization occurs regularly in wild Heliconius butterflies, although hybrid individuals are usually very rare. However, hybridization generally occurs only between the most closely related species. We report a rare naturally occurring hybrid between non-sister species and carry out the first genetic analysis of such distant hybridization. Mitochondrial and nuclear genes indicate that the specimen is an F1 hybrid between a female Heliconius ethilla and a male Heliconius melpomene, originating from a group of 13 species estimated to have diverged over 2.5 Myr ago. The presence of such distant natural hybrids, together with evidence for backcrossing, suggests that gene flow across species boundaries can take place long after speciation. Adaptive genes such as those involved in wing coloration could thus be widely shared among members of this highly mimetic genus.     

Superparasitism in Cotesia glomerata does not benefit the host plant by reduction of herbivory caused by Pieris brassicae

Superparasitism occurs in Cotesia glomerata L. (Hymenoptera: Braconidae), a gregarious endoparasitoid of Pieris spp. (Lepidoptera: Pieridae). The responses of Pieris brassicae L. larvae to superparasitism were examined in order to elucidate the ecological significance of this behaviour. Models of tritrophic interactions often imply that attraction of herbivore natural enemies by the plant constitutes a defence. Parasitoid attack on herbivores is assumed to result in a reduction in herbivory and or an increase in plant fitness. Coupled with the active involvement of the plant in producing signals, this can be seen as an indirect mediation of wound induced defence. The results show that superparasitism of P. brassicae by the parasitoid C. glomerata reduced survivorship but increased food consumption and weight growth in P. brassicae larvae. The duration of host larval development was found prolonged as the number of oviposition increased and superparasitized larvae (three to five time parasitized) grew slower than unparasitized larvae or larvae parasitized one or two times.     

Ontogenetic patterns in the mechanisms of tolerance to herbivory in Plantago

Background and Aims

Herbivory and plant defence differ markedly among seedlings and juvenile and mature plants in most species. While ontogenetic patterns of chemical resistance have been the focus of much research, comparatively little is known about how tolerance to damage changes across ontogeny. Due to dramatic shifts in plant size, resource acquisition, stored reserves and growth, it was predicted that tolerance and related underlying mechanisms would differ among ontogenetic stages.

Methods

Ontogenetic patterns in the mechanisms of tolerance were investigated in Plantago lanceolata and P. major (Plantaginaceae) using the genetic sib-ship approach. Pot-grown plants were subjected to 50 % defoliation at the seedling, juvenile and mature stages and either harvested in the short-term to look at plasticity in growth and photosynthesis in response to damage or allowed to grow through seed maturation to measure phenology, shoot compensation and reproductive fitness.

Key Results

Tolerance to defoliation was high in P. lanceolata, but low in P. major, and did not vary among ontogenetic stages in either species. Mechanisms underlying tolerance did vary across ontogeny. In P. lanceolata, tolerance was significantly related to flowering (juveniles) and pre-damage shoot biomass (mature plants). In P. major, tolerance was significantly related to pre-damage root biomass (seedlings) and induction of non-photochemical quenching, a photosynthetic parameter (juveniles).

Conclusions

Biomass partitioning was very plastic in response to damage and showed associations with tolerance in both species, indicating a strong role in plant defence. In contrast, photosynthesis and phenology showed weaker responses to damage and were related to tolerance only in certain ontogenetic stages. This study highlights the pivotal role of ontogeny in plant defence and herbivory. Additional studies in more species are needed to determine how seedlings tolerate herbivory in general and whether mechanisms vary across ontogeny in consistent patterns.     

入侵植物黄顶菊生长、再生能力对模拟天敌危害的响应

缺乏专性天敌可能是外来植物扩散蔓延的原因之一.生物防治是环境友好且高效的防除方法,而人工模拟天敌危害对植物的生长、再生指标影响的效果与自然天敌的效果相似.在田间条件下,对入侵植物黄顶菊进行不同程度模拟天敌危害处理,探讨对黄顶菊生长、再生能力影响的效果,为生物防治提供理论基础.结果表明,轻度处理和摘顶处理下黄顶菊生物量、株高、分枝数、花蕾数、净光合速率(Pn)、水分利用效率(WUE)指标表现出超补偿效应,只有重度处理下受到显著抑制;轻度至重度处理初始荧光(F0)则显著高于对照和摘顶处理,而PSⅡ的最大光化学效率(Fv/Fm)和PSⅡ的潜在活性(FV/F0)则显著降低.分析发现,分枝数、花蕾数、生物量等具很高的表型可塑性指数,显示黄顶菊的生长指标对模拟天敌危害具有更强的适应能力.综上,轻度天敌危害对黄顶菊无明显抑制作用,重度危害对黄顶菊的生长、开花结实抑制效果最为理想.生产实践中建议结合其他方法以实现对黄顶菊的有效控制.     

Sensitivity of growth and biomass allocation patterns to increasing nitrogen: a comparison between ephemerals and annuals in the Gurbantunggut Desert,north-western China

Background and Aims

Biomass accumulation and allocation patterns are critical to quantifying ecosystem dynamics. However, these patterns differ among species, and they can change in response to nutrient availability even among genetically related individuals. In order to understand this complexity further, this study examined three ephemeral species (with very short vegetative growth periods) and three annual species (with significantly longer vegetative growth periods) in the Gurbantunggut Desert, north-western China, to determine their responses to different nitrogen (N) supplements under natural conditions.

Methods

Nitrogen was added to the soil at rates of 0, 0·5, 1·0, 3·0, 6·0 and 24·0 g N m⁻² year⁻¹. Plants were sampled at various intervals to measure relative growth rate and shoot and root dry mass.

Key Results

Compared with annuals, ephemerals grew more rapidly, increased shoot and root biomass with increasing N application rates and significantly decreased root/shoot ratios. Nevertheless, changes in the biomass allocation of some species (i.e. Erodium oxyrrhynchum) in response to the N treatment were largely a consequence of changes in overall plant size, which was inconsistent with an optimal partitioning model. An isometric log shoot vs. log root scaling relationship for the final biomass harvest was observed for each species and all annuals, while pooled data of three ephemerals showed an allometric scaling relationship.

Conclusions

These results indicate that ephemerals and annuals differ observably in their biomass allocation patterns in response to soil N supplements, although an isometric log shoot vs. log root scaling relationship was maintained across all species. These findings highlight that different life history strategies behave differently in response to N application even when interspecific scaling relationships remain nearly isometric.     

The acceptability of meadow plants to the slug Deroceras reticulatum and implications for grassland restoration

Background and Aims

Despite the selective pressure slugs may exert on seedling recruitment there is a lack of information in this context within grassland restoration studies. Selective grazing is influenced by interspecific differences in acceptability. As part of a larger study of how slug–seedling interactions may influence upland hay meadow restoration, an assessment of relative acceptability is made for seedlings of meadow plants to the slug, Deroceras reticulatum.

Methods

Slug feeding damage to seedling monocultures of 23 meadow species and Brassica napus was assessed in microcosms over 14 d. The severity and rate of damage incurred by each plant species was analysed with a generalized additive mixed model. Plant species were then ranked for their relative acceptability.

Key Results

Interspecific variation in relative acceptability suggested seedlings of meadow species form a hierarchy of acceptability to D. reticulatum. The four most acceptable species were Achillea millefolium and the grasses Holcus lanatus, Poa trivialis and Festuca rubra. Trifolium pratense was acceptable to D. reticulatum and was the second highest ranking forb species. The most unacceptable species were mainly forbs associated with the target grassland, and included Geranium sylvaticum, Rumex acetosa, Leontodon hispidus and the grass Anthoxanthum odoratum. A strong positive correlation was found for mean cumulative feeding damage and cumulative seedling mortality at day 14.

Conclusions

Highly unacceptable species to D. reticulatum are unlikely to be selectively grazed by slugs during the seedling recruitment phase, and were predominantly target restoration species. Seedlings of highly acceptable species may be less likely to survive slug herbivory and contribute to seedling recruitment at restoration sites. Selective slug herbivory, influenced by acceptability, may influence community-level processes if seedling recruitment and establishment of key functional species, such as T. pratense is reduced.     

Major trends in stem anatomy and growth forms in the perianth-bearing Piperales,with special focus on Aristolochia

Background and Aims

The order Piperales has the highest diversity of growth forms among the earliest angiosperm lineages, including trees, shrubs, climbers and herbs. However, within the perianth-bearing Piperales (Asarum, Saruma, Lactoris, Hydnora, Prosopanche, Thottea and Aristolochia), climbing species only occur in the most species-rich genus Aristolochia. This study traces anatomical and morphological traits among these lineages, to detect trends in growth form evolution and developmental processes.

Methods

Transverse stem sections of different developmental stages of representatives of Asarum, Saruma, Lactoris, Hydnora, Thottea and Aristolochia were compared and anatomical traits were linked to growth form evolution. Biomechanical properties of representative climbers were determined in three-point bending tests and are discussed based on the anatomical observations. Growth form evolution of the perianth-bearing Piperales was reconstructed by ancestral character state reconstruction using Mesquite.

Key Results

While species of Asarum and Saruma are exclusively herbaceous, species of the remaining genera show a higher diversity of growth habit and anatomy. This growth form diversity is accompanied by a more complex stem anatomy and appropriate biomechanical properties. The ancestral growth form of the perianth-bearing Piperales is reconstructed with either a shrub-like or herbaceous character state, while the following three backbone nodes in the reconstruction show a shrub-like character state. Accordingly, the climbing habit most probably evolved in the ancestor of Aristolochia.

Conclusions

Since the ancestor of the perianth-bearing Piperales has been reconstructed with a herb- or shrub-like habit, it is proposed that the climbing habit is a derived growth form, which evolved with the diversification of Aristolochia, and might have been a key feature for its diversification. Observed anatomical synapomorphies, such as the perivascular fibres in Lactoris, Thottea and Aristolochia, support the phylogenetic relationship of several lineages within the perianth-bearing Piperales. In addition, the hypothesis that the vegetative organs of the holoparasitic Hydnoraceae are most probably rhizomes is confirmed.     

Contributions to the faunistics and bionomics of Staphylinidae (Coleoptera) in northeastern North America: discoveries made through study of the University of Guelph Insect Collection, Ontario, Canada

Staphylinidae (Rove Beetles) from northeastern North America deposited in the University of Guelph Insect Collection (Ontario, Canada) were curated from 2008-2010 by the first author. The identification of this material has resulted in the recognition of thirty-five new provincial or state records, six new Canadian records, one new record for the United States and two new records for eastern Canada. All records are for subfamilies other than Aleocharinae and Pselaphinae, which will be treated in future publications as collaborative projects. Range expansions of ten exotic species to additional provinces and states are reported. The known distributions of each species in northeastern North America are summarized and presented as maps, and those species with a distinctive habitus are illustrated with color photographs. Genitalia and/or secondary sexual characters are illustrated for those species currently only identifiable on the basis of dissected males. The majority of the new records are in groups that have been recently revised, demonstrating the importance of curation and local insect surveys to the understanding of biodiversity, even for taxa and areas considered 'relatively well-known'.     

Host plant and population determine the fitness costs of resistance to Bacillus thuringiensis

Novel adaptations often cause pleiotropic reductions in fitness. Under optimal conditions individual organisms may be able to compensate for, or reduce, these fitness costs. Declining environmental quality may therefore lead to larger costs. We investigated whether reduced plant quality would increase the fitness costs associated with resistance to Bacillus thuringiensis in two populations of the diamondback moth Plutella xylostella. We also measured the rate of decline in resistance on two host-plant (Brassica) species for one insect population (Karak). Population X plant species interactions determined the fitness costs in this study. Poor plant quality increased the fitness costs in terms of development time for both populations. However, fitness costs seen in larval survival did not always increase as plant quality declined. Both the fitness and the stability experiment indicated that fitness costs were higher on the most suitable plant for one population. Theoretically, if the fitness cost of a mutation interacts additively with environmental factors, the relative fitness of resistant insects will decrease with environmental quality. However, multiplicative costs do not necessarily increase with declining quality and may be harder to detect when fitness parameters are more subject to variation in poorer environments.     

Population Genetics and Identity of an Introduced Terrestrial Slug: Arion subfuscus s.l. in the North-east USA (Gastropoda, Pulmonata, Arionidae)

Several European species of the terrestrial slug genus Arion have been introduced into North America. A case in point is the species complex A. subfuscus s.l. which has become one of the most abundant slug taxa in North America. In Europe this complex consists of at least two cryptic species, viz. A. fuscus and A. subfuscus s.s., the latter of which is further subdivided in five strongly divergent mtDNA lineages (A. subfuscus S1–S5). In order to determine which of these A. subfsucus s.l. taxa are present in the NE USA and in order to assess their population genetic structure, we compared mtDNA, nDNA and allozyme variation between populations from the NE USA and Europe. Our results show that (1) at least A. subfuscus S1 has become successfully established in the NE USA, (2) founder effects are the most likely explanation for the loss of a large amount of molecular genetic variation in populations from the NE USA (i.e. a loss of 96% of the 16S rDNA haplotypes, 67% of the ITS1 alleles and 46% of the alleles at polymorphic allozyme loci), and (3) part of the remaining genetic variation in NE USA populations was probably due to multiple introductions from the British Isles and the European mainland, and the hybrid structure of most of these source populations. Apparently, the extreme loss of molecular genetic variation in this introduced species has not prevented it from successfully establishing and spreading in novel environments.