Plant structural defences against browsing birds: a legacy of New Zealand's extinct moas

Browsing by large vertebrates has been a major force in the evolution of terrestrial plants but Holocene extinctions of the browsers have left a legacy of broken biotic partnerships. Ratite birds were the largest herbivores in several regions, such as the moas of New Zealand. Many woody plants there have a distinct form of branching, described as "divaricate", with thin, wide angled, branches intertwining to form a tangled canopy. Divaricate branching has been interpreted as a form of protection against climate extremes or as an anachronistic defense against the extinct moas. Here we report the first experimental evidence that many of these plants are defended against extant ratite browsers. In feeding experiments on two tree species with different (heteroblastic) juvenile and adult branch morphology, emus and ostriches obtained adequate feeding rates from adult shoots but sub-maintenance feeding rates from juvenile shoots with the ratite-resistant traits. Divaricate juvenile shoots suffered 30–70% less biomass removal to the birds than adult shoots. Ratites browse by a distinctive clamping and tugging action. Structural defence traits that exploit the limitations of this feeding mode include narrow, strong, elastic branches that resist being torn off, wide branching angle ("divaricate") that makes shoots difficult to swallow, and small, widely spaced leaves. This novel plant architectural defence has developed in at least 20% of the native woody flora of New Zealand, including 10 heteroblastic tree species that exhibit the ratite-resistant strategy until they reach ca 3 metres height. It is also a major axis of variation amongst homoblastic woody shrub species. The defences are useless against mammalian browsers that shear shoots, contributing to marked decreases in the abundances of ratite-resistant species in New Zealand after the introduction of mammals.     

An investigation into induced plant defences

This laboratory exercise involves techniques that can be used to investigate induced plant defences. Runner beans are damaged, and the leaves that subsequently grow are tested for the presence of additional defence mechanisms. A control (undamaged) group is kept for comparison. Induced physical defences are indicated by an increase in the density of hairs (trichomes) on the leaves, and induced chemical defences by a decrease in the palatability of the leaves. The latter is tested by a bioassay using garden snails. These basic methods can be used to investigate a variety of defensive responses in plants.     

An automatic method for assessing structural importance of amino acid positions

Background  

A great deal is known about the qualitative aspects of the sequence-structure relationship, for example that buried residues are usually more conserved between structurally similar homologues, but no attempts have been made to quantitate the relationship between evolutionary conservation at a sequence position and change to global tertiary structure. In this paper we demonstrate that the Spearman correlation between sequence and structural change is suitable for this purpose.     

Herbivore specific induction of silica-based plant defences

Induced plant responses to herbivory have major impacts on herbivore feeding behaviour, performance and population dynamics. These effects are well established for chemical defences, but induction of physical defences remains far less studied. However, for many plants, it is physical defences that play the major role in regulating the levels of herbivore damage sustained. We provide evidence that, in grasses, induction of physical defences is both specific to herbivore feeding, as opposed to mechanical damage, and may be dependant on the amount of damage imposed. Furthermore, we show that the magnitude of the induction response is sufficient to deter further damage and affect herbivore performance. We compared silica induction in two grass species in response to vertebrate and invertebrate damage, and to mechanical defoliation. Induction was assessed at two levels of damage over 16 months. Foliar silica content did not increase in response to mechanical defoliation, but damage by either voles or locusts resulted in increases in silica content of over 400%. This increase deterred feeding by both voles and locusts. Silica induction in grasses due to repeated damage events over a prolonged period suggests a possible role for silica defence in the cyclical population fluctuations observed in many grass-feeding herbivores.     

Inhibition of lipoxygenase affects induction of both direct and indirect plant defences against herbivorous insects

Herbivore-induced plant defences influence the behaviour of insects associated with the plant. For biting–chewing herbivores the octadecanoid signal-transduction pathway has been suggested to play a key role in induced plant defence. To test this hypothesis in our plant—herbivore—parasitoid tritrophic system, we used phenidone, an inhibitor of the enzyme lipoxygenase (LOX), that catalyses the initial step in the octadecanoid pathway. Phenidone treatment of Brussels sprouts plants reduced the accumulation of internal signalling compounds in the octadecanoid pathway downstream of the step catalysed by LOX, i.e. 12-oxo-phytodienoic acid (OPDA) and jasmonic acid. The attraction of Cotesia glomerata parasitoids to host-infested plants was significantly reduced by phenidone treatment. The three herbivores investigated, i.e. the specialists Plutella xylostella, Pieris brassicae and Pieris rapae, showed different oviposition preferences for intact and infested plants, and for two species their preference for either intact or infested plants was shown to be LOX dependent. Our results show that phenidone inhibits the LOX-dependent defence response of the plant and that this inhibition can influence the behaviour of members of the associated insect community.     

Use of the leukocyte adherence inhibition reaction for assessing the effectiveness of vaccination against measles

The reaction of the inhibition of leukocyte adhesion to a glass slide under the action of measles antigen may be used for the evaluation of the activity of antigen-specific T-lymphocytes in the process of immunization against measles and recommended, along with serological studies, for finding out persons susceptible to measles among vaccinees. The immunological effect of booster immunizations against measles can be evaluated by the degree of the inhibition of leukocyte agglutination to a glass slide.     

Induced systemic resistance (ISR) against pathogens in the context of induced plant defences

Induced systemic resistance (ISR) of plants against pathogens is a widespread phenomenon that has been intensively investigated with respect to the underlying signalling pathways as well as to its potential use in plant protection. Elicited by a local infection, plants respond with a salicylic-dependent signalling cascade that leads to the systemic expression of a broad spectrum and long-lasting disease resistance that is efficient against fungi, bacteria and viruses. Changes in cell wall composition, de novo production of pathogenesis-related-proteins such as chitinases and glucanases, and synthesis of phytoalexins are associated with resistance, although further defensive compounds are likely to exist but remain to be identified. In this Botanical Briefing we focus on interactions between ISR and induced resistance against herbivores that is mediated by jasmonic acid as a central signalling molecule. While many studies report cross-resistance, others have found trade-offs, i.e. inhibition of one resistance pathway by the other. Here we propose a framework that explains many of the thus far contradictory results. We regard elicitation separately from signalling and from production, i.e. the synthesis of defensive compounds. Interactions on all three levels can act independently from each other.     

Evidence of induced plant defences in a pondweed

SUMMARY. 1. Palatability changes, induced by herbivore damage, have received much attention in terrestrial plant-insect research but negligible investigation in freshwater systems.
2. Potamogeton coloratus (Potamogetonaceae) and the folivorous caddis larva Triaenodes bicolor (Insecta: Trichoptera) were used to duplicate bioassay techniques common in terrestrial plant-insect research.
3. Leaves of P. coloratus were artificially damaged. Grazing on damaged leaves, and undamaged leaves from damaged plants, was compared to that on control leaves from undamaged plants up to 10 days after initial damage.
4. The palatability of damaged and undamaged leaves from damaged plants declined compared to control leaves. The differences were significant at 5 days after damage, but had recovered to approximately equal palatability after 10 days.     

Genetics of resistance against defences of the host plant Barbarea vulgaris in a Danish flea beetle population

One essential aspect of the study of the evolution of host-plant use by insects is (variation in) its genetic basis. The genetic basis of the ability of a flea beetle (Phyllotreta nemorum) to use the crucifer Barbarea vulgaris ssp. arcuata (G type) as a host plant was studied in a Danish population (Kvaerkeby) occurring naturally on this atypical host plant. Evidence was found that this ability was determined by a single, major, autosomal gene, although the presence of genes at additional loci at lower frequencies could not be excluded. No evidence was found for sex-linked inheritance, which was common in a second population in Denmark (Ejby) using Barbarea as a host plant. All beetles in the Kvaerkeby sample were homozygous 'resistant' to Barbarea defence. After crossing resistant F1 offspring from pairs consisting of a field-collected beetle and a susceptible one amongst each other, genotyping the F2 (reared on radish) showed a 1:2:1 ratio of homozygous resistant, heterozygous and susceptible beetles. No evidence was found for a reduction in the viability of beetles that were homozygous resistant at the autosomal locus, in contrast to what had been found earlier for two backcrossed lines founded by beetles from Ejby. The results show that there is variation in the genetic basis of host-plant use across local populations and imply that population structure should form part of the study of the interaction between P. nemorum and its host plants.     

Inter-generational equity index for assessing environmental sustainability: An example on global warming

Inter-generational equity is essential for environmental sustainability. The current generation inherits an environment with a certain quality from the previous generation. The impact on the environment gradually exacerbates and accumulates over a period of time between two generations. However, currently there is no index available to assess inter-generational equity. Generally a typical environmental index is established to represent the environmental status in a specific year. This kind of index, although it presents the annual environmental variation, does not reflect the degree of change in environmental sustainability between two generations. Therefore, an inter-generational equity index (IGEI) and an endowment equation to examine the temporal trend of the changing environment are proposed for assessing inter-generational equity. To demonstrate the applicability of the endowment equation, an IGEI was established to assess the inter-generational equity of global warming. The global warming IGEI evaluates the status between two generations based on three sub-indexes; CO₂ emission, loss due to climate disasters, and the size of the existing forest area. The pressure–state–response (PSR) framework was adopted to explain the causal relationship between these three sub-indexes. According to the endowment rate determined by the proposed equation for each sub-index, the increase in CO₂ emission from 1980 to 2000 shows an obviously inequitable pattern between generations. Subsequently, the loss due to climate disasters between generations was also more serious. The size of the forest area, an important factor for reducing the impact of global warming, is unfortunately also decreasing significantly between generations. Using the endowment rate determined by the proposed endowment equation, the evaluation of the inter-generational equity is made possible and is demonstrated by the IGEI established for global warming.     

An easy-to-use index of ecological integrity for prioritizing freshwater sites and for assessing habitat quality

Prioritizing and assessing the condition of sites for conservation action requires robust and ergonomic methodological tools. We focus here on prioritizing freshwater sites using two promising biodiversity indices, the Dragonfly Biotic Index (DBI) and Average Taxonomic Distinctness (AvTD). The AvTD had no significant association with either species richness or endemism. In contrast, the DBI was highly significantly associated with species richness and endemism, although the strengths of the associations were weak. These associations are related to how the sub-indices in the DBI are weighted, and how species are distributed geographically. Additionally, the DBI was found to be very useful for site selection based on its ability to measure ecological integrity, combined with level of threat, at multiple spatial scales. The AvTD was found to be useful principally for regional use. As the DBI is a low-cost, easy-to-use method, it has the additional use as a method for assessing habitat quality and recovery in restoration programs. The DBI operates at the species level, and is therefore highly sensitive to habitat condition and has great potential for environmental assessment and monitoring freshwater biodiversity and quality. Practical, worked examples of river restoration are given here. In view of the ease and versatility by which the DBI can be employed, we recommend its testing and possible integration into freshwater management and conservation schemes elsewhere in the world.     

An index of weed size for assessing the soil productivity of ancient crop fields

A method is presented for generating data on archaeological weed species relevant to soil productivity and consequently crop husbandry. Three plant attributes (maximum canopy height, maximum canopy spread and maximum dry leaf weight per node) which are functionally related to habitat productivity were measured for 161 British annual species. These three attributes were combined to produce an index of weed size. Index values were found to differ significantly between character species of phytosociological classes from fertile and infertile habitats and to provide an objective assessment of CSR (Competitor/Stress-tolerator/Ruderal) strategysensu Grime (1974, 1979). Further work is required, however, to distinguish medium-sized species that exploit highly disturbed and productive habitats from those of less disturbed and less productive situations.     

Timing of white-tailed deer browsing affects wetland plant communities

White-tailed deer (Odocoileus virginianus Zimm.) have the potential to alter plant community composition and successional trajectory by browsing differentially on forb, graminoid, and woody species. The objective of this study was to determine if seasonal elimination of deer browsing changed wetland plant community composition and structure. We established 66 deer exclosure plots in two wetland vegetation communities in Canaan Valley, West Virginia, USA. Plots were established in April 2005 and monitoring was conducted in June and October, 2005–2007 to obtain data on both early and late species. Composition differed between control and treatment plots in Solidago spp.–Rubus hispidus L. communities in late-protected plots (enclosed July–October) when data were gathered in October. Community composition also varied in early-protected plots (enclosed April–July) when data were gathered in June. Forb cover increased in treatment plots in Solidago spp.–Rubus hispidus communities. Composition differed in Populus tremuloides Michx. communities in late-protected and continuously protected plots. There was no increase in cover by any wetland indicator status categories after 2 years of protection. Timing of browse played an influential role in the effect that white-tailed deer have on wetland plant communities. Our results suggest that reducing browsing pressure seasonally can increase forb species cover.     

Biofilm image reconstruction for assessing structural parameters

The structure of biofilms can be numerically quantified from microscopy images using structural parameters. These parameters are used in biofilm image analysis to compare biofilms, to monitor temporal variation in biofilm structure, to quantify the effects of antibiotics on biofilm structure and to determine the effects of environmental conditions on biofilm structure. It is often hypothesized that biofilms with similar structural parameter values will have similar structures; however, this hypothesis has never been tested. The main goal was to test the hypothesis that the commonly used structural parameters can characterize the differences or similarities between biofilm structures. To achieve this goal (1) biofilm image reconstruction was developed as a new tool for assessing structural parameters, (2) independent reconstructions using the same starting structural parameters were tested to see how they differed from each other, (3) the effect of the original image parameter values on reconstruction success was evaluated, and (4) the effect of the number and type of the parameters on reconstruction success was evaluated. It was found that two biofilms characterized by identical commonly used structural parameter values may look different, that the number and size of clusters in the original biofilm image affect image reconstruction success and that, in general, a small set of arbitrarily selected parameters may not reveal relevant differences between biofilm structures.     

Ecological and evolutive implications of bacterial defences against predators

Bacterial communities are often heavily consumed by microfaunal predators, such as protozoa and nematodes. Predation is an important cause of mortality and determines the structure and activity of microbial communities in both terrestrial and aquatic ecosystems, and bacteria evolved various defence mechanisms helping them to resist predation. In this review, I summarize known antipredator defence strategies and their regulation, and explore their importance for bacterial fitness in various environmental conditions, and their implications for bacterial evolution and diversification under predation pressure. I discuss how defence mechanisms affect competition and cooperation within bacterial communities. Finally I present some implications of bacterial defence mechanisms for ecosystem services provided by microbial communities, such as nutrient cycling, virulence and the biological control of plant diseases.     

The jasmonate pathway alters herbivore feeding behaviour: consequences for plant defences

The jasmonate pathway is a highly conserved defensive cascade in plants that regulates the induction of resistance against herbivores; however, its role in herbivore feeding behaviour remains unknown. We used a mutant tomato plant (def‐1) deficient in the production of jasmonate‐related defensive proteins to test the hypothesis that genotypes with a reduced ability to induce resistance have a higher and more concentrated pattern of herbivore damage. Wild‐type and def‐1 plants received either damage by Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) caterpillars or no damage. After treatment, we tested for systemic responses by allowing a free roaming S. exigua caterpillar to feed on the undamaged portions of plants. Weight‐gain and leaf consumption of S. exigua were highest on def‐1 plants, regardless of prior herbivore damage. Def‐1 plants also had fewer numbers of leaves and leaflets eaten, and fewer feeding holes, which was indicative of a more concentrated distribution of damage on mutant compared to wild‐type plants. Following these results, we mimicked the amount and distribution of feeding damage that wild‐type or jasmonate‐deficient plants would receive on wild‐type plants to test whether changes in feeding behaviour may feedback to influence the expression of induced resistance. We mimicked the distribution of damage in wild‐type and jasmonate‐deficient plants by allowing caterpillars to feed on either one (leaf 1 or 2) or two leaves (leaf 1 and 2). Increased herbivore damage resulted in higher proteinase inhibitor (PI) activity, a jasmonate‐regulated defensive protein, and lower S. exigua performance on wild‐type but not jasmonate‐deficient plants. Compared to undamaged plants, a concentrated pattern of herbivore damage increased systemic resistance; these induced responses were greater on leaflets with stronger vascular connections to the damaged leaf. A more dispersed pattern of caterpillar damage altered the expression of induced responses, but the outcome depended on the specific pattern of damage. When leaf 1 was damaged and then leaf 2, the undamaged (third) leaf (which is more strongly connected to leaf 1 than 2) expressed reduced the PI activity compared to plants receiving concentrated damage to leaf 1; whereas in plants where leaf 2 was first damaged and then leaf 1, there were no differences in PI activity in leaf 3 compared to plants receiving concentrated damage to leaf 2. Thus, induction of the jasmonate pathway may not only determine the amount and distribution of feeding damage by herbivores, but this may feedback to affect the subsequent expression of plant defence.     

Experience in using P. hamadryas for assessing the effectiveness of a peroral vaccination method against plague]

For the first time P. hamadryas were used for studying the effectiveness of oral immunization with dried live plague vaccine. Oral immunization was shown to produce morphological changes in the organs and tissues of the monkeys, which indicated the immune transformation of the organism. The challenge of the immunized animals with the infective agent introduced in aerosol showed the effectiveness of the inhalation and oral methods of immunization. P. hamadryas proved to be a suitable model for the evaluation of the effectiveness of oral vaccination. A more precise quantitative evaluation of the effectiveness of oral vaccination against plague requires further research.