Resistance and tolerance to herbivory in Salix cordata are affected by different environmental factors

Abstract.  1. Effects of sand burial and nutrients on the ability of sand-dune willow ( Salix cordata ) to tolerate or resist herbivory by the beetle Altica subplicata were evaluated in field experiments.
2. To assess tolerance, all combinations of sand burial (none, 50%), nutrients (presence, absence), and beetles (presence, absence) were applied to caged plants and growth responses to herbivory were measured. Sand burial increased plant growth rate, but decreased S. cordata 's tolerance to herbivory. Although nutrients increased growth, tolerance to herbivory was unaffected.
3. To assess resistance, plants were exposed to all combinations of sand burial and nutrients, and then to natural beetle colonisation. The presence of nutrients, but not sand burial, significantly increased the percentage of plants with beetles, for both adults and larvae. This decreased resistance to beetles of plants grown with added nutrients occurred only in the absence of sand burial.
4. The performance and preference of beetles were examined in laboratory experiments. Larvae developed faster and had increased pupation success on plants with nutrients added. Beetles also showed a marginally significant feeding preference for leaves grown with added nutrients. Thus, S. cordata tolerance to herbivory was affected by sand burial, whereas resistance, preference, and performance were affected by nutrient level.     

Consequences of insect herbivory on grape fine root systems with different growth rates

Herbivory tolerance has been linked to plant growth rate where plants with fast growth rates are hypothesized to be more tolerant of herbivory than slower-growing plants. Evidence supporting this theory has been taken primarily from observations of aboveground organs but rarely from roots. Grapevines differing in overall rates of new root production, were studied in Napa Valley, California over two growing seasons in an established vineyard infested with the sucking insect, grape phylloxera (Daktulosphaira vitifoliae Fitch). The experimental vineyard allowed for the comparison of two root systems that differed in rates of new root tip production (a 'fast grower', Vitis berlandieri x Vitis rupestris cv. 1103P, and a slower-growing stock, Vitis riparia x Vitis rupestris cv. 101-14 Mgt). Each root system was grafted with a genetically identical shoot system (Vitis vinifera cv. Merlot). Using minirhizotrons, we did not observe any evidence of spatial or temporal avoidance of insect populations by root growth. Insect infestations were abundant throughout the soil profile, and seasonal peaks in phylloxera populations generally closely followed peaks in new root production. Our data supported the hypothesis that insect infestation was proportional to the number of growing tips, as indicated by similar per cent infestation in spite of a threefold difference in root tip production. In addition, infested roots of the fast-growing rootstock exhibited somewhat shorter median lifespans (60 d) than the slower-growing rootstock (85 d). Lifespans of uninfested roots were similar for the two rootstocks (200 d). As a consequence of greater root mortality of younger roots, infested root populations in the fast-growing rootstock had an older age structure. While there does not seem to be a trade-off between potential growth rate and relative rate of root infestation in these cultivars, our study indicates that a fast-growing root system may more readily shed infested roots that are presumably less effective in water and nutrient uptake. Thus, differences in root tip production may be linked to differences in the way plants cope with roots that are infested by sucking insects.     

环境和基因型对刺参幼参表型变异和生长的影响

将6个刺参幼参全同胞家系置于E1(高密度,自然光周期)、E2(低密度,全黑暗)和E3(低密度,自然光周期)3种不同环境下养殖60 d,通过建立模型分析环境、基因型及环境与基因型互作对刺参幼参成活率、生长性状的特定生长率和变异系数的影响.结果表明:环境、基因型及其互作对刺参幼参成活率无显著性影响(P＞0.05);环境对刺参幼参体长和体重的特定生长率有极显著性影响(P＜0.01),对其变异系数无显著性影响;基因型对刺参幼参体长和体重的特定生长率、体长变异系数有极显著性影响,对刺参幼参体重变异系数有显著性影响(P＜0.05);基因型与环境互作对刺参幼参体长和体重的特定生长率、变异系数均无显著性影响,因此实验室育种过程中可忽略家系与环境(光周期和密度)互作的影响;E3环境下有利于刺参幼参的生长,其体长和体重的平均特定生长率可达0.03％和1.58％.本研究为刺参家系育种和建立刺参健康养殖模式提供理论依据.     

Will plant vigor and tolerance be genetically correlated? Effects of intrinsic growth rate and self-limitation on regrowth

Plants are known to maintain fitness despite herbivore attack by a variety of damage-induced mechanisms. These mechanisms are said to confer tolerance, which can be measured as the slope of fitness over the proportion of plant biomass removed by herbivore damage. It was recently supposed by Stowe et al. (2000) that another plant property, general vigor, has little effect on tolerance. We developed simple models of annual monocarpic plants to determine if a genetic change in components of growth vigor will also change the fitness reaction to damage. We examined the impact of intrinsic growth rate on the tolerance reaction norm slope assuming plants grow geometrically, i.e., without self-limitation. In this case an increase in intrinsic growth rate decreases tolerance (the reaction norm slope becomes more negative). A logistic growth model was used to examine the impact of self-limiting growth on the relationship between intrinsic growth rate and the tolerance reaction norm slope. With self-limitation, the relationship is sensitive to the timing of attack. When attack is early and there is time for regrowth, increasing growth rate increases tolerance (slope becomes less negative). The time limitations imposed by late attack prevent appreciable regrowth and induce a negative relationship between growth rate and tolerance. In neither of these simple cases will the correlation between vigor and tolerance constrain selection on either trait. However, a positive correlation between growth rate and self-limitation will favor fast growth/strong self-limitation in a high-damage environment, but slow growth/weak self-limitation in a low-damage environment. Thus, fundamental growth rules that determine vigor have constitutive effects on tolerance. The net costs and benefits of damage-induced tolerance mechanisms will thus be influenced by the background imposed by fundamental growth rules. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of the specialist herbivore Luehdorfia puziloi on the performance of a woodland herbaceous plant, Asarum heterotropoides

Plants show many responses to herbivore damage caused by insects. We investigated the effect of the specialist leaf herbivore Luehdorfia puziloi on the performance of a deciduous forest understory perennial herb Asarum heterotropoides . We conducted artificial defoliation experiments with different levels of damage (0, 50 or 100% clipping) in the early growing period (flowering time: early May) and in the late growing period (when natural herbivory by L. puziloi larvae occurs: early June) in a natural population. Effects of the defoliation treatments on reproduction (seed-set ratio) of A. heterotropoides in the treated year and on survival and development of the plant in the subsequent year were investigated. Severe defoliation conducted in the early period resulted in less current-year seed production and increased regression to a dormant or non-reproductive stage in the following year, which would reduce the probability of future flowering. In contrast, defoliation conducted in the late period had no effect on the reproduction, survival and development of A. heterotropoides . Similarly, we found no obvious correlation between the damaged leaf area during the later period and seed set. Our results show that the specialist herbivore L. puziloi did not influence the performance of A. heterotropoides by damaging the plant later in the season when it was tolerant of damage.     

螺类牧食与沉积物类型对苦草生长的影响

在室外实验条件下,研究了螺类牧食与沉积物类型对苦草生长的影响。结果表明:椭圆萝卜螺的牧食对苦草生长有显著影响,牧食损害使苦草的相对生长率明显降低、块茎数量及重量下降。沉积物类型对苦草生长也有明显影响,苦草的相对生长率在营养盐相对丰富的湖泥处理组中要远高于岸泥处理组,而根须数与块茎重量在湖泥处理组中显著低于岸泥处理组。螺类牧食与沉积物类型对苦草的各项生长指标无明显交互作用。     

Susceptibility of willow clones (Salix spp.) to herbivory by Phyllodecta vulgatissima (L.) and Galerucella lineola (Fab.) (Coleoptera, Chrysomelidae)

Levels of damage by mixed natural infestations of the leaf-feeding chrysomelid beetles, Phyllodecta vulgatissima (L.) (the blue willow beetle) and Galerucella lineola (Fab.) (the brown willow beetle), were determined in replicated field plots of 24 Salix clones at Long Ashton (Bristol, UK) during 1993–94. Over the same period, the host plant preferences of both chrysomelids were investigated in a standard multiple-choice laboratory procedure, where beetles were enclosed in Petri dishes with leaf discs cut from young pot-grown trees propagated from shoot cuttings taken from 20 of the 24 willow clones represented in the field study. The laboratory experiments indicated that P. vulgatissima and G. lineola had similar host plant preferences in the range of willows examined (r >0.85). In both field and laboratory, the least preferred Salix clones and hybrids were those of 5. eriocephala, followed by S. purpurea, S. burjatica, S. dasyclados and S. triandra. Clones of S. eriocephala and S. purpurea were frequently rejected altogether in laboratory tests. Most preferred were clones of S. viminalis and several hybrids of S. viminalis, S. aurita, S. caprea and S. cinerea. These results substantiate the reports that P. vulgatissima and G. lineola are deterred from feeding on willows which have relatively high concentrations of phenolic (salicylate) glucosides in the leaves. The least preferred willows, particularly S. eriocephala, S. purpurea and S. burjatica, could be of great potential value in plant breeding for resistance to these willow beetle pests.     

Effects of genetic variability and habitat of Qualea parviflora (Vochysiaceae) on herbivory by free-feeding and gall-forming insects

• Background and Aims Differences in the chemical and physical traits of plants caused by both genetic and habitat characteristics may influence attack by herbivores. Leaves of Qualea parviflora (Vochysiaceae), a common tree of different habitats in the Brazilian Neotropical savannas (cerrado), are susceptible to severe attack by herbivorous free-living and gall-forming insects. Attack by free-living and gall-forming insects within and between populations of Q. parviflora were examined and it was determined to what extent genetic variability (detected by RAPD markers), phenotypic characteristics of the plants and habit traits influence the number of free-living and gall-forming insect species and individuals attacking the plants, and the intensity of attack.• Methods On four occasions in 2000, leaves were sampled from ten individual trees in each of three types of vegetation in the cerrado: campo sujo, cerrado sensu stricto and cerradão at the Ecological Station of Pirapitinga (ESP), in Três Marias, north-western Minas Gerais, Brazil. Genetic variability was detected by RAPD markers, and concentrations of nutrients, phenols and tannins, sclerophylly and pre-dawn water potential of leaves were measured. Water and nutrient contents in the soil below each tree characterized the habitat. The free-living and gall-forming herbivorous insects were determined.• Key Results Of 69 RAPD markers analysed, 41 were polymorphic and were used for analyses of genetic variability of Q. parviflora. Most of the variability occurred within habitats, accounting for 97·65 % of the genetic variability. Plants in the cerrado sensu stricto and campo sujo were the most similar. There were no significant associations between genetic similarity and the chemical and physical traits of Q. parviflora, or with habitat, nor was there significant correlation between phenotypic and habitat traits. Increasing concentrations of tannins and sulphur, C : N ratio and sclerophylly correlated with increasing percentage of leaf area damaged by herbivores. Decreased sclerophylly, concentration of tannins and C : N ratio, and increased concentration of nutrients in leaves correlated with increased severity of attack by gall-forming insects.• Conclusions Nutrient concentration in the soil had more influence, indirectly, on free-feeding insects than did composition of Q. parviflora leaves. However, gall-forming insects are affected more by leaf quality, attacking fewer sclerophyllous leaves, with larger nutrient but smaller tannin concentrations.Key words: Cerrado, genetic variability, gall attack, herbivory, insect galls, plant quality, Qualea parviflora, RAPD, Vochysiaceae     

Effects of pepper (Capsicum chinense) genotypic diversity on insect herbivores

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Effects of experimental inbreeding on herbivore resistance and plant fitness: the role of history of inbreeding, herbivory and abiotic factors

Inbreeding is common in plant populations and can affect plant fitness and resistance against herbivores. These effects are likely to depend on population history. In a greenhouse experiment with plants from 17 populations of Lychnis flos-cuculi, we studied the effects of experimental inbreeding on resistance and plant fitness. Depending on the levels of past herbivory and abiotic factors at the site of plant origin, we found either inbreeding or outbreeding depression in herbivore resistance. Furthermore, when not damaged experimentally by snail herbivores, plants from populations with higher heterozygosity suffered from inbreeding depression and those from populations with lower heterozygosity suffered from outbreeding depression. These effects of inbreeding and outbreeding were not apparent under experimental snail herbivory. We conclude that inbreeding effects on resistance and plant fitness depend on population history. Moreover, herbivory can mask inbreeding effects on plant fitness. Thus, understanding inbreeding effects on plant fitness requires studying multiple populations and considering population history and biotic interactions.     

Exotic invasive black willow (Salix nigra) in Australia: influence of hydrological regimes on population dynamics

Floodplain vegetation occupies disturbance prone habitats vulnerable to exotic plant invasion. Black willow (Salix nigra Marshall) is a flood-tolerant tree native to the southeastern United States and recently invasive in Australia, where it is considered detrimental to riparian environments. Effective management of S. nigra requires understanding the impacts of hydrological conditions on population dynamics at each stage of the plant’s life cycle. The influence of inundation events (timing, duration, and recession rates) on S. nigra stand dynamics and relative growth rate (RGR) was quantified across a hydrological gradient on the shorelines of Blowering Dam reservoir (NSW, Australia). Successful recruitment (sexual and asexual) and establishment is highly dependent on the position of S. nigra recruits above reservoir water levels and exposure to flooding during the first few years of establishment. Recruitment was ubiquitous along the hydrological gradient but a greater number of asexual recruits were found at higher elevations where inundation events are less frequent. Juvenile mortality was highest at lower elevations, which experienced greater depth and duration of inundation. Mean RGR was greatest in S. nigra stands experiencing no inundation over the study period and declined as inundation duration increased. Flooding events inhibit adult growth, but create suitable conditions for seedling recruits, provided the depth and duration of the flood does not exceed complete submersion for more than 30 days. To investigate relative tolerance to water table decline rooted S. nigra cuttings were grown in rhizopods, controlled growth devices that allow water-table manipulation. Water-table decline rates of 0, 1, 2, 4, and 8 cm day⁻¹ were applied and the response of leaf abscission measured. S. nigra cuttings were not significantly impacted at water-table decline rates of between 1 and 4 cm day⁻¹. Spatial location of S. nigra recruits in Australian floodplains represents a trade-off among hydrological conditions that promote recruitment without inducing mortality, resulting in a narrow spatial and temporal regeneration window critical to successful establishment. Future distribution and abundance of S. nigra in Australia will be determined by propagule availability and the degree to which current and future flow regimes create suitable hydrological conditions for successful establishment.     

Florivory: the intersection of pollination and herbivory

Plants interact with many visitors who consume a variety of plant tissues. While the consequences of herbivory to leaves and shoots are well known, the implications of florivory, the consumption of flowers prior to seed coat formation, have received less attention. Herbivory and florivory can yield different plant, population and community outcomes; thus, it is critical to distinguish between these two types of consumption. Here, we consider the ecological and evolutionary consequences of florivory. A growing number of studies recognize that florivory is common in natural systems and in some cases surpasses leaf herbivory in magnitude and impact. Florivores can affect male and female plant fitness via direct trophic effects and through altered pathways of species interactions. In particular, florivory can affect pollination and have consequences for plant mating and floral sexual system evolution. Plants are not defenceless against florivore damage. Concepts of resistance and tolerance can be applied to plant–florivore interactions. Moreover, extant theories of plant chemical defence, including optimal defence theory, growth rate hypothesis and growth differentiation–balance hypothesis, can be used to make testable predictions about when and how plants should defend flowers against florivores. The majority of the predictions remain untested, but they provide a theoretical foundation on which to base future experiments. The approaches to studying florivory that we outline may yield novel insights into floral and defence traits not illuminated by studies of pollination or herbivory alone.     

Additive effects of genotype,nutrient availability and type of tissue damage on the compensatory response of Salix planifolia ssp. planifolia to simulated herbivory

Plant responses to herbivory include tolerance (i.e. compensatory growth) and defense. Several factors influence the tolerance of a plant following herbivory, including plant genetic identity, site nutrient availability, and previous and/or concurrent herbivory. We studied the effects of these factors on the compensatory response of Salix planifolia ssp. planifolia, a shrub species common in the boreal and subarctic regions of North America. We cloned several genets of S. planifolia and submitted them to simulated root and/or leaf herbivory while varying the nutrient availability. Simulated leaf herbivory was more detrimental to the plant than simulated root herbivory, reducing both above- and below-ground tissue production. Leaf demography was unaffected by either simulated herbivory treatment. There was some compensatory growth following simulated leaf and root herbivory, but only the root compartment responded to increased nutrient availability. Simulated leaf herbivory increased leaf transpiration and reduced stomatal resistance, suggesting increased carbon fixation. The unexpected finding of the experiment was the absence of interactions among factors (genotype, nutrient availability and type of tissue damage) on the compensatory response of S. planifolia. These factors thus have additive effects on the species' compensatory ability.     

Effects of plant quality and ant defence on herbivory rates in a neotropical ant‐plant

1. Understanding the degree to which populations and communities are limited by both bottom‐up and top‐down effects is still a major challenge for ecologists, and manipulation of plant quality, for example, can alter herbivory rates in plants. In addition, biotic defence by ants can directly influence the populations of herbivores, as demonstrated by increased rates of herbivory or increased herbivore density after ant exclusion. The aim of this study was to evaluate bottom‐up and top‐down effects on herbivory rates in a mutualistic ant‐plant. 2. In this study, the role of Azteca alfari ants as biotic defence in individuals of Cecropia pachystachya was investigated experimentally with a simultaneous manipulation of both bottom‐up (fertilisation) and top‐down (ant exclusion) factors. Four treatments were used in a fully factorial design, with 15 replicates for each treatment: (i) control plants, without manipulation; (ii) fertilised plants, ants not manipulated; (iii) unfertilised plants and excluded ants and (iv) fertilised plants and ants excluded. 3. Fertilisation increased the availability of foliar nitrogen in C. pachystachya, and herbivory rates by chewing insects were significantly higher in fertilised plants with ants excluded. 4. Herbivory, however, was more influenced by bottom‐up effects – such as the quality of the host plant – than by top‐down effects caused by ants as biotic defences, reinforcing the crucial role of leaf nutritional quality for herbivory levels experienced by plants. Conditionality in ant defence under increased nutritional quality of leaves through fertilisation might explain increased levels of herbivory in plants with higher leaf nitrogen.     

莲草直胸跳甲取食对空心莲子草和莲子草克隆整合的影响

很多外来入侵植物都具有克隆生长习性,探究克隆整合特性与外来克隆植物入侵性间的关系对阐明其生态适应性及入侵机制具有重要的意义。本研究以入侵植物空心莲子草及其本地同属种莲子草为研究对象,比较在生防昆虫莲草直胸跳甲的取食下,克隆整合对两种植物先端分株、基端分株及整个克隆片段生长和生物量分配的影响。结果表明: 在莲草直胸跳甲取食下,有克隆整合的空心莲子草先端分株的叶片数、茎长、分株数及整个克隆片段的地径均显著高于无克隆整合植株,其基端分株及整个克隆片段的地下生物量和总生物量相较于无克隆整合植株分别降低了78.2%、60.9%和48.7%、37.2%;有克隆整合的莲子草先端分株的地径及整个克隆片段的叶片数与无克隆整合植株相比显著增加,其基端分株数显著降低了21.7%,而其先端分株、基端分株及整个克隆片段的生物量均无显著差异。耗益分析表明,在莲草直胸跳甲取食下,空心莲子草先端分株的分株数与生物量及莲子草先端分株的分株数均能通过克隆整合显著受益,而两种植物基端的分株数、生物量的耗益则不受克隆整合处理的影响。这些结果表明,克隆整合虽能在一定程度缓解莲草直胸跳甲对于两种植物先端分株的取食压力,且空心莲子草的克隆整合作用要强于莲子草,但在整个克隆片段水平上,两种植物并不能通过克隆整合显著获益。     

Effects of environmental enrichment on survivorship,growth, sex ratio and behaviour in laboratory maintained zebrafish Danio rerio

Environmental enrichment involves increasing the complexity of a fish's environment in order to improve welfare. Researchers are legally obliged to consider the welfare of laboratory animals and poor welfare may result in less robust data in experimental science. Laboratory zebrafish Danio rerio are usually kept in bare aquaria for ease of husbandry and, despite being a well-studied species, little is known about how laboratory housing affects their welfare. This study shows that environmental enrichment, in the form of the addition of gravel substratum and plants into the tank, affects survivorship, growth and behaviour in laboratory-maintained D. rerio. Larvae reared in enriched tanks had significantly higher survivorship compared with larvae reared in bare tanks. Effects of the tank conditions on growth were more variable. Females from enriched tanks had a higher body condition than females maintained in bare tanks, but intriguingly this was not the case for males, where the only difference was a more variable body condition in males maintained in bare tanks. Sex ratio in the rearing tanks did not differ between treatments. Resource monopolisation was higher for fish in enriched tanks than for those in bare tanks. Fish from enriched tanks displayed lower levels of behaviours associated with anxiety compared with fish from bare tanks when placed into a novel environment. Thus, this study demonstrates differences in welfare for D. rerio maintained under different environmental conditions with enhancements in welfare more commonly associated with tank enrichment.     

Elephant herbivory of knob-thorn (Senegalia nigrescens) and ivory palm (Hyphaene petersiana) in Bwabwata National Park,Caprivi, Namibia: The role of ivory palm as a biotic refuge

African elephants have major impacts on vegetation, particularly at high densities. Knob-thorns (Senegalia nigrescens) are typically ring-barked by elephant, and high levels of mortality are common at high elephant densities. Our study aimed to test whether ivory palm clusters (Hyphaene petersiana) form a biotic refuge for knob-thorn against elephant herbivory. We measured the density, damage and mortality of knob-thorns in sites differing according to ivory palm presence and elephant density, and thus, the probability of knob-thorn encounter by elephants. The site with palms and low elephant density, had a high density of knob-thorns, but lower proportions of damaged and dead trees, than sites without palms but with similar or higher elephant density. In the former, knob-thorns were associated with palm clusters, particularly saplings and young adults. In this site, low proportions of damaged and dead knob-thorns were recorded in palm clusters, compared with outside clusters, and to those in the other sites. Our study also showed that juvenile palms which protected knob-thorns, suffered low mortality in contrast to subadult palms. We have no evidence but implicate elephants and suggest that in palm clusters, subadult palms are more accessible to elephants than knob-thorns because of the different methods of utilisation.