UV-screening of grasses by plant silica layer?

UV-screening by terrestrial plants is a crucial trait since colonization of terrestrial environments has started. In general, it is enabled by phenolic substances. Especially for grasses it remains unclear why plants grown under the absence of UV-B-radiation exhibit nonetheless a high UV-B-screening potential. But this may be explained by the UV-screening effect of the silicon double layer. It was shown for seedlings of soybeans (Glycine max L.) and wheat (Triticum aestivum L.) that enhanced silicon supply reduces stress induced by UV-radiation. Even more important is a direct correlation between silicon content in the epidermis near area (intercellular spaces) and the absorption of UV-radiation in this area shown in other papers. The silicon double layer may act like a glass layer and decreases the transmission of UV-radiation at the epidermis near area. In summary, the absorbance/reflection of ultraviolet radiation is dependent on the characteristics of the epidermis near area of leaves, particularly the occurrence (qualitatively and quantitatively) of phenolic substances and/or a silicon double layer in this area. Consequently, UV-screening by plant silicon double layer should get more attention in future research with emphasis on effects of UV-radiation on plant physiology.     

Does leaf ontogeny lead to changes in defensive strategies against insect herbivores?

Plants use different defense strategies throughout their ontogenetic development. In this study, three questions were proposed: (1) Is there a greater abundance of ants on young leaves, which possess active extrafloral nectaries, than on mature leaves? (2) Do ants exert an indirect defense that is effective against the attack of herbivorous insects? (3) Do mature leaves have a greater concentration of physical and chemical defense than young leaves? These questions were addressed through an ant-exclusion experiment in which two branches of Copaifera langsdorffii (n = 25) were marked and monitored throughout the entire foliar expansion and development period. A reduction in the abundance of ants throughout foliar development was observed. The ants exerted an effective defense against herbivores on C. langsdorffii: the branches where ants were excluded had a greater number of herbivores. The mature leaves possessed a greater index of leaf sclerophylly than young leaves, but the leaves did not differ in the concentration of tannins. The foliar ontogeny of C. langsdorffii promoted an inversion in the defense strategy against herbivores, and despite showing an opportunistic relationship, the interaction between ants and extrafloral nectaries appears to play an important role in structuring the interactions between herbivorous insects and their host plants.     

Can metals defend plants against biotic stress?

Farmers have used metal compounds in phytosanitary treatments for more than a century; however, it has recently been suggested that plants absorb high concentrations of metals from the substrate as a self-defense mechanism against pathogens and herbivores. This metal defense hypothesis is among the most attractive proposals for the 'reason to be' of metal hyperaccumulator species. On a molecular basis, metal defense against biotic stress seems to imply common and/or complementary pathways of signal perception, signal transduction and metabolism. This does not imply a broad band of co-resistance to different stress types but reflects a continuous cross talk during the coevolution of plants, pathogens and herbivores competing in an environment where efficient metal ion acquisition and ion homeostasis are essential for survival.     

Gamma-aminobutyrate: defense against invertebrate pests?

Gamma-aminobutyrate (GABA) is a ubiquitous four-carbon, non-protein amino acid. In plants, stress-induced GABA accumulation is well documented. However, the role(s) of GABA accumulation is contentious. In this Opinion article, we argue that wounding due to herbivory and crawling by insect larvae causes rapid GABA accumulation via the disruption of cellular compartmentation and the release of the acidic vacuolar contents to the cytosol. The activity of glutamate decarboxylase, the cytosolic enzyme responsible for GABA synthesis, has an acidic pH optimum. Subsequent GABA ingestion has a plant defense function by directly acting on GABA-regulated invertebrate neuromuscular junctions. Plants with an enhanced GABA-producing capacity reduce herbivory by invertebrate pests. These findings suggest that GABA accumulation is a rapidly deployed, local resistance mechanism that constitutes a first line of defense in deterring herbivory.     

Are silica defences in grasses driving vole population cycles?

Understanding the factors that drive species population dynamics is fundamental to biology. Cyclic populations of microtine rodents have been the most intensively studied to date, yet there remains great uncertainty over the mechanisms determining the dynamics of most of these populations. For one such population, we present preliminary evidence for a novel mechanism by which herbivore-induced reductions in plant quality alter herbivore life-history parameters and subsequent population growth. We tested the effect of high silica levels on the population growth and individual performance of voles (Microtus agrestis) reared on their winter food plant (Deschampsia caespitosa). In sites where the vole population density was high, silica levels in D. caespitosa leaves collected several months later were also high and vole populations subsequently declined; in sites where the vole densities were low, levels of silica were low and population density increased. High silica levels in their food reduced vole body mass by 0.5% a day. We argue that silica-based defences in grasses may play a key role in driving vole population cycles.     

Does functional redundancy of communities provide insurance against human disturbances? An analysis using regional-scale stream invertebrate data

Human-induced reductions in species richness might alter the quality of ecosystem services when the remaining species are not able to substitute the functions provided by extirpated species. We examined how human disturbances (nutrient enrichment, land use intensification, instream habitat degradation and the presence of alien species) influence the species richness of stream invertebrates. Stream invertebrates (425 native species) were collected by kick and sweep sampling technique at 274 stream sites covering the entire area of Hungary. We measured the species richness, functional richness (i.e. number of unique functional roles provided by community members) and functional redundancy (i.e. the functional insurance of the community) using information on the feeding habits of each species. To remove the effect of natural variability, we tested the effect of stressors on the residuals of models relating species richness, functional richness and functional redundancy with natural environmental gradients. Our results showed that species richness was negatively influenced by instream habitat degradation and nutrient enrichment. Independent of the way of quantifying functional richness and functional redundancy, we found that functional richness is more sensitive to human impact than functional redundancy of stream invertebrates. The finding that a reduction of species richness is associated with a loss of unique functional roles (functional richness) is important for conservation issues, because the number of unique functional roles is usually regarded as driver of ecosystem functioning.     

Can plants use an entomopathogenic virus as a defense against herbivores?

It is by now well established that plants use various strategies to defend themselves against herbivores. Besides conventional weapons such as spines and stinging hairs and sophisticated chemical defenses, plants can also involve the enemies of the herbivores in their defense. It has been suggested that plants could even use entomopathogens as part of their defense strategies. In this paper, we show that Brassica oleraceae plants that are attacked by Myzus persicae aphids infected with an entomopathogenic parvovirus (M. persicae densovirus) transport the virus through the phloem locally and systematically. Moreover, healthy aphids that fed on the same leaf, but separated from infected aphids were infected via the plant. Hence, this is proof of the principle that plants can be vectors of an insect virus and can possibly use this virus as a defense against herbivores.     

Benevolent herbivores?

Two questions dominate current thinking on plant-herbivore interactions: what is the impact of feeding by herbivores on the distribution and abundance of plants; and what is the role of herbivory as an agency of natural selection, leading to differential performance of host plant genotypes? These two questions come together in discussions of how the evolutionary consequences of herbivory are manifest at the population and ecosystem levels.     

Plant chemical defense against herbivores and pathogens: generalized defense or trade-offs?

Plants are often attacked by multiple enemies, including pathogens and herbivores. While many plant secondary metabolites show specific effects toward either pathogens or herbivores, some can affect the performance of both these groups of natural enemies and are considered to be generalized defense compounds. We tested whether aucubin and catalpol, two iridoid glycosides present in ribwort plantain (Plantago lanceolata), confer in vivo resistance to both the generalist insect herbivore Spodoptera exigua and the biotrophic fungal pathogen Diaporthe adunca using plants from P. lanceolata lines that had been selected for high- and low-leaf iridoid glycoside concentrations for four generations. The lines differed approximately three-fold in the levels of these compounds. Plants from the high-selection line showed enhanced resistance to both S. exigua and D. adunca, as evidenced by a smaller lesion size and a lower fungal growth rate and spore production, and a lower larval growth rate and herbivory under both choice and no-choice conditions. Gravimetric analysis revealed that the iridoid glycosides acted as feeding deterrents to S. exigua, thereby reducing its food intake rate, rather than having post-ingestive toxic effects as predicted from in vitro effects of hydrolysis products. We suggest that the bitter taste of iridoid glycosides deters feeding by S. exigua, whereas the hydrolysis products formed after tissue damage following fungal infection mediate pathogen resistance. We conclude that iridoid glycosides in P. lanceolata can serve as broad-spectrum defenses and that selection for pathogen resistance could potentially result in increased resistance to generalist insect herbivores and vice versa, resulting in diffuse rather than pairwise coevolution.     

Does plant phylogenetic diversity increase invertebrate herbivory in managed grasslands?

Plant diversity and land-use intensity have been shown to affect invertebrate herbivory. Several hypotheses predict positive (e.g. associational susceptibility) or negative (e.g. associational resistance) relationships of herbivory with plant species richness. Also, the strength and direction of reported relationships vary greatly between studies leading to the conclusion that relationships either depend on the specific system studied or that other unconsidered factors are more important. Here, we hypothesized that plant phylogenetic diversity is a stronger predictor of invertebrate herbivory than plant species richness because it integrates additional information about the phenotypical and functional composition of communities. We assessed the community-wide invertebrate herbivory, plant species richness and phylogenetic diversity across a range of land-use intensities including a total of 145 managed grasslands in three regions in Germany. Increasing land-use intensity decreased plant species richness and phylogenetic diversity. Plant species richness did not predict invertebrate herbivory. By contrast herbivory moderately increased with increasing plant phylogenetic diversity even after accounting for the effects of region and land use. The strength of direct effects of land-use intensity and indirect effects via altered phylogenetic diversity on herbivory, however, varied among regions. Our results suggest that increasing phylogenetic diversity of plant communities increases invertebrate herbivory probably by providing higher resource diversity. Differences between regions underline the need to account for regional peculiarities when attempting to generalize land-use effects on invertebrate herbivory.     

Does vitamin D protect against DNA damage?

Vitamin D is a secosteroid best known for its role in maintaining bone and muscle health. Adequate levels of vitamin D may also be beneficial in maintaining DNA integrity. This role of vitamin D can be divided into a primary function that prevents damage from DNA and a secondary function that regulates the growth rate of cells. The potential for vitamin D to reduce oxidative damage to DNA in a human has been suggested by clinical trial where vitamin D supplementation reduced 8-hydroxy-2'-deoxyguanosine, a marker of oxidative damage, in colorectal epithelial crypt cells. Studies in animal models and in different cell types have also shown marked reduction in oxidative stress damage and chromosomal aberrations, prevention of telomere shortening and inhibition of telomerase activity following treatment with vitamin D. The secondary function of vitamin D in preventing DNA damage includes regulation of the poly-ADP-ribose polymerase activity in the DNA damage response pathway involved in the detection of DNA lesions. It is also able to regulate the cell cycle to prevent the propagation of damaged DNA, and to regulate apoptosis to promote cell death. Vitamin D may contribute to prevention of human colorectal cancer, though there is little evidence to suggest that prevention of DNA damage mediates this effect, if real. Very limited human data mean that the intake of vitamin D required to minimise DNA damage remains uncertain.     

Will chemical defenses become more effective against specialist herbivores under elevated CO2?

Elevated atmospheric CO₂ is known to affect plant–insect herbivore interactions. Elevated CO₂ causes leaf nitrogen to decrease, the ostensible cause of herbivore compensatory feeding. CO₂ may also affect herbivore consumption by altering chemical defenses via changes in plant hormones. We considered the effects of elevated CO₂, in conjunction with soil fertility and damage (simulated herbivory), on glucosinolate concentrations of mustard (Brassica nigra) and collard (B. oleracea var. acephala) and the effects of leaf nitrogen and glucosinolate groups on specialist Pieris rapae consumption. Elevated CO₂ affected B. oleracea but not B. nigra glucosinolates; responses to soil fertility and damage were also species‐specific. Soil fertility and damage also affected B. oleracea glucosinolates differently under elevated CO₂. Glucosinolates did not affect P. rapae consumption at either CO₂ concentration in B. nigra, but had CO₂‐specific effects on consumption in B. oleracea. At ambient CO₂, leaf nitrogen had strong effects on glucosinolate concentrations and P. rapae consumption but only gluconasturtiin was a feeding stimulant. At elevated CO₂, direct effects of leaf nitrogen were weaker, but glucosinolates had stronger effects on consumption. Gluconasturtiin and aliphatic glucosinolates were feeding stimulants and indole glucosinolates were feeding deterrents. These results do not support the compensatory feeding hypothesis as the sole driver of changes in P. rapae consumption under elevated CO₂. Support for hormone‐mediated CO₂ response (HMCR) was mixed; it explained few treatment effects on constitutive or induced glucosinolates, but did explain patterns in SEMs. Further, the novel feeding deterrent effect of indole glucosinolates under elevated CO₂ in B. oleracae underscores the importance of defensive chemistry in CO₂ response. We speculate that P. rapae indole glucosinolate detoxification mechanisms may have been overwhelmed under elevated CO₂ forcing slowed consumption. Specialists may have to contend with hosts with poorer nutritional quality and more effective chemical defenses under elevated CO₂.     

Does bee or wasp mimicry by orchid flowers also deter herbivores?

General visual bee mimicry and specific chemical mimicry by flowers to solitary female bees or wasps are well known in several orchid genera, for example, the Mediterranean genus Ophrys, the Australian genera Cryptostylis and Chiloglottis, and the South-African Disa. This mimicry has been shown to attract solitary male bees or wasps, which are their species-specific pollinators. The visual and chemical signals are considered to be a type of deceptive pollination mechanism based on mimicry for the exploitation of perceptual biases of animals. We propose that in addition to this unique pollination mechanism, these plants exhibit another, rarely mentioned and practically forgotten, non-exclusive function of bee or wasp mimicry (Batesian mimicry). This mimicry may deter large mammalian herbivores, and possibly also insects from the plants and especially from their flowers by a type of visual and olfactory deceptive aposematism. While visiting the flowers, bees and wasps may add a Müllerian effect to this defense. We extend this hypothesis to many other rewarding flowers that are bee or wasp pollinated and propose that abundance of pollinating bees or wasps may deter herbivorous mammals and insects from the plants during their peak flowering season.     

Does it always pay to defend one's nest? A case study in African penguin

Throughout the animal kingdom, individual variation in reproductive success is commonly observed, even under similar environmental conditions. However, the mechanisms behind such differences remain unclear. The notion of behavioural consistency in animals has developed rapidly since the early 21st century partly as an approach to understand among‐individual differences. In this context, a number of studies have highlighted the influence of pair assortment in personality on breeding success. In this study, we related breeding success to individual behaviour, specifically a risk‐taking behaviour, and pair assortment per behaviour in African penguins (Spheniscus demersus) over two breeding seasons of contrasting food availability. On Bird Island, Algoa Bay, South Africa, we used indices of boldness and overall mobility in penguins’ nest defence behaviour as a response to a standard pedestrian approach during chick‐rearing. These behaviours were consistent over the trials and indicated these traits may be related to personality in African penguins. Individuals were categorized as risk‐prone (“bold,” “mobile”) or risk‐averse (“shy,” “non‐mobile”). We then assessed their breeding success through chick growth and survival over 4 weeks in 2015 and 2016. There was weak positive assortment of pairs in relation to nest defence behaviour. However, pair assortment did not significantly influence birds’ breeding success. Shy penguins were generally the most successful (had the highest chick growth rates), which was especially apparent during a food shortage in 2016, possibly reflecting a higher energy investment when foraging. In contrast, chicks from bold parents grew significantly slower, especially in 2016. Bold parents may defend their nest successfully against predation or intra‐specific aggression when food is abundant, but when predation risks are limited and food availability is low, this strategy may not be beneficial. In the context of climate change, where food shortage events may become more frequent, risk‐averse individuals may be favoured and genetic diversity may be reduced in African penguins.     

Facilitation of tree saplings by nurse plants: Microhabitat amelioration or protection against herbivores?

Question: Positive interactions are predicted to be common in communities developing under high physical stress or high herbivory pressure due to neighbour amelioration of limiting physical and consumer stresses, respectively. However, when both stress sources meet in the same community, the relative importance of the two facilitation mechanisms is poorly understood. We ask: What is the relative importance of abiotic vs. biotic mechanisms of facilitation of tree saplings by shrubs in Mediterranean mountain forests? Location: Sierra Nevada, SE Spain (1800–1850 m a.s.l.) Methods: Saplings of four tree taxa (Acer opalus ssp. grana‐tense, Quercus ilex, Pinus nigra ssp. salzmanii and P. sylvestris var. nevadensis) were planted following a 2 × 2 factorial design: two levels of herbivory (control and ungulate exclusion) and two microhabitats (under shrubs and in open areas). Sapling survival and growth were monitored for five years. Results: Shrubs had positive effects on sapling survival both in control and ungulate excluded plots. This effect was species‐specific, with shrubs increasing the survival of Acer opalus and Quercus ilex three and twofold, respectively, but having a minor effect on the Pinus species. Herbivory damage was also species‐specific, being much higher for Acer opalus than for any other species. Shrubs did not protect saplings of any species against ungulates. Thus, all Acer saplings (the most damaged species) suffered herbivory outside the exclosures, which largely reduced sapling height. Conclusions: Protection from abiotic stress (summer drought and winter frost) was much more relevant than protection from biotic stress (herbivory). However, we propose that the final balance between the two mechanisms can be expected to vary strongly between sites, depending on the relative magnitude of the different sources of stress and the intrinsic traits (e.g. palatability) of the species interacting.     

Are extrafloral nectaries efficient against herbivores? Herbivory and plant defenses in contrasting tropical species

植物用于防御的资源有限,而那些具有生物防御的物种,其叶片可能会较少地用于其他类型的防御。我们比较了机械防御能力较弱,但具有花外蜜腺的植物,与没有花外蜜腺但叶片更有韧性的植物是否更不容易被取食。我们通过分析文献数据,调查有无花外蜜腺的植物被取食的情况。在巴西南部的热带稀树草原植被中,我们采集了6种热带植物的叶片数据,并测定了被取食情况和比叶面积。我们进一步评估了有无花外蜜腺的物种之间以及植物之间被取食情况和比叶面积的差异。为了检验动物取食与叶片韧性之间的关系,我们对单株平均被取食情况和平均叶片韧性进行了回归。研究结果表明,植物表现出不同程度的叶片损伤,但没有蚂蚁防御的植物因被取食造成的叶面积损失最大。不同植物的机械防御水平也不相同。无花外蜜腺的植株更坚韧,比叶面积值更小。虽然无花外蜜腺的植物有更多的坚硬叶片,但这种机械防御不足以损害和/或减少食草动物的取食,这表明由蚂蚁形成的生物防御可能比用于与叶片适口性相关的机械防御更有效。     

Does the MRCGP examination discriminate against Asian doctors?

OBJECTIVE--To ascertain whether the membership examination for the Royal College of General Practitioners (MRCGP) discriminates against doctors of Indian subcontinent ethnic origin ("Asian doctors"). DESIGN--Retrospective analysis of data from five administrations of the MRCGP examination (December 1988-December 1990). SETTING--United Kingdom national examination body. SUBJECTS--3686 doctors taking the examination for the first time, 244 of whom were classified as Asian, the remainder as non-Asian. MAIN OUTCOME MEASURES--Comparison of performance in each of the written and oral components of the examination between Asian doctors, identified by their names and classified into subgroups by countries of birth and primary medical training from data provided at registration, and non-Asian doctors. RESULTS--On written components of the examination (multiple choice paper mean score Asians versus non-Asians 42.3 v 48.6, modified essay paper 40.9 v 48.9, practice topic/critical reading paper 41.5 v 48.7, all p less than 0.001 by t testing). But analysis by countries of birth and primary training showed that these differences were due largely to poor performance by certain groups of Asian doctors, especially those born and trained in the Indian subcontinent or elsewhere outside the United Kingdom. Asian doctors born and trained in the United Kingdom and those born in Africa or the West Indies and trained in the United Kingdom performed similarly to the non-Asian doctors. CONCLUSIONS--The examination does not systematically discriminate against Asian doctors, but the poor performance of the two subgroups of Asians is cause for serious concern and requires investigation.     

Does macrophyte fractal complexity drive invertebrate diversity,biomass and body size distributions?

Habitat structure is one of the fundamental factors determining the distribution of organisms at all spatial scales, and vegetation is of primary importance in shaping the structural environment for invertebrates in many systems. In the majority of biotopes, invertebrates live within vegetation stands of mixed species composition, making estimates of structural complexity difficult to obtain. Here we use fractal indices to describe the structural complexity of mixed stands of aquatic macrophytes, and these are employed to examine the effects of habitat complexity on the composition of free-living invertebrate assemblages that utilise the habitat in three dimensions. Macrophytes and associated invertebrates were sampled from shallow ponds in southwest England, and rapid digital image analysis was used to quantify the fractal complexity of all plant species recorded, allowing the complexity of vegetation stands to be reconstructed based on their species composition. Fractal indices were found to be significantly related to both invertebrate biomass–body size scaling and overall invertebrate biomass; more complex stands of macrophytes contained a greater number of small animals. Habitat complexity was unrelated to invertebrate taxon richness and macrophyte surface area and species richness were not correlated with any of the invertebrate community parameters. The biomass–body size scaling relationship of lentic macroinvertebrates matched those predicted by models incorporating both allometric scaling of resource use and the fractal dimension of a habitat, suggesting that both habitat fractal complexity and allometry may control density–body size scaling in lentic macroinvertebrate communities.