Cascading Effects of Climate Change: Do Hurricane‐damaged Forests Increase Risk of Exposure to Parasites?

Increased parasitism in animals in disturbed habitats is often understood to be the result of increased disease susceptibility due to low food availability resulting in nutritionally stressed and immunocompromised individuals. Such habitat change, however, might also lead to increased exposure to disease. In this article, we test measures of susceptibility and exposure to explain the prevalence and intensity of directly and indirectly transmitted helminths in black howler monkeys (Alouatta pigra) following a hurricane in Belize. None of these parasites were predicted by direct measures of susceptibility (as measured by fruit consumption and fecal cortisol levels). Rather, directly transmitted parasites (Trichuris sp. and strongylid type eggs.) were predicted by host density and group size, both measures of exposure. Similarly, only the consumption of Cecropia peltata, a fast growing pioneer that has a mutualistic relationship with ants predicted levels of the indirectly transmitted trematode Controrchis spp., also suggesting exposure. Cecropia peltata also increased in density post‐hurricane, was high in digestible protein, sugar, and salt and eaten by monkeys more frequently than predicted based on distribution. These data suggest that in this hurricane‐damaged forest the ingestion of this abundant and nutritious pioneer species increased exposure of the monkeys to Controrchis through ingestion of ant intermediate hosts. These results may point to a pattern true of pioneer species in general, leaving animals in disturbed forests with higher levels of parasitism as a result of changes to forest structure. As severe weather events are expected to increase, this suggests a cascading effect of climate change on ecosystem interactions and disease ecology.     

Polyglutamylation: a fine‐regulator of protein function?

Polyglutamylation is a post-translational modification in which glutamate side chains of variable lengths are formed on the modified protein. It is evolutionarily conserved from protists to mammals and its most prominent substrate is tubulin, the microtubule (MT) building block. Various polyglutamylation states of MTs can be distinguished within a single cell and they are also characteristic of specific cell types or organelles. Polyglutamylation has been proposed to be involved in the functional adaptation of MTs, as it occurs within the carboxy-terminal tubulin tails that participate directly in the binding of many structural and motor MT-associated proteins. The discovery of a new family of enzymes that catalyse this modification has brought new insight into the mechanism of polyglutamylation and now allows for direct functional studies of the role of tubulin polyglutamylation. Moreover, the recent identification of new substrates of polyglutamylation indicates that this post-translational modification could be a potential regulator of diverse cellular processes.     

Localized outbreak of a willow leaf beetle: plant vigor or natural enemies?

The possible roles of plant quality (vigor) and natural enemies in the development of a localized out-break of the leaf beetle Galerucella lineola (Coleoptera: Chrysomelidae) in a stand of Salix cinerea were investigated. Caged and uncaged larvae on six bushes in the outbreak area were compared with caged and uncaged larvae on six bushes in an adjacent nonoutbreak area in terms of performance. In 1997, when the studies were performed, the natural density of the insect (beetles plus eggs) was six times higher in the outbreak area compared with the nonoutbreak area. Even though the vigor (measured as shoot length) of bushes in the outbreak was 72% higher than that of bushes in the nonoutbreak area, we found no difference between areas in the performance (survival, developmental time, pupal weight) of caged larvae or in the willingness of caged females to lay eggs. Among larvae exposed to natural enemies, the disappearance rate was significantly higher in the nonoutbreak area. The density of generalist predators was significantly higher in the nonoutbreak than in the outbreak area. We conclude that differences in plant quality, despite the observed difference in plant vigor, could not explain the observed difference in beetle density between areas. Lower predation pressure in the outbreak area could, however, not be excluded as a possible reason for the higher density of leaf beetles in this area. Received: October 18, 1999 / Accepted: February 4, 2000     

Can the pheromones of predators modulate responses to herbivore‐induced plant volatiles?

Biological control of greenhouse pests has been successfully developed and applied. In greenhouse crops, several entomophagous species (predators and parasitoids) are used simultaneously in the crop cycle. One important aspect of these crops, which represent modified ecosystems, is the interactions among complexes of species, including plants, phytophagous insects, and predators. The chemical relationships (semiochemicals: pheromones and kairomones) among these species likely play an important role in greenhouse crops; however, few studies have focused on these relationships. The aim of this study was to analyse the importance of semiochemicals. Three groups of laboratory trials were conducted with two predatory species: Nabis pseudoferus and Nesidiocoris tenuis (Hemiptera: Nabidae and Miridae, respectively). The results of the first group of trials indicated that the adult females of both species were more attracted to herbivore‐induced plant volatiles (HIPVs) than they were to the control plants or plants with artificial damage. Based on the second group of trials, pheromones triggered an attraction in adult females of both species for conspecifics. Finally, based on the interactions of the adult females of the same species, pheromones changed or modulated the predatory responses to HIPVs. The implications of these results for the biological control of pest species in greenhouses are further discussed.     

Between‐year variation of MHC allele frequencies in great reed warblers: selection or drift?

The major histocompatibility complex (MHC) genes are extremely polymorphic and this variation is assumed to be maintained by balancing selection. Cyclic interactions between pathogens and their hosts could generate such selection, and specific MHC alleles or heterozygosity at certain MHC loci have been shown to confer resistance against particular pathogens. Here we compare the temporal variation in allele frequencies of 23 MHC class I alleles with that of 23 neutral microsatellite markers in adult great reed warblers (a passerine bird) in nine successive cohorts. Overall, the MHC alleles showed a significantly higher variation in allele frequencies between cohorts than the microsatellite alleles, using a multi-variate genetic analysis (amova). The frequency of two specific MHC alleles, A3e (P = 0.046) and B4b (P = 0.0018), varied more between cohorts than expected from random, whereas none of the microsatellite alleles showed fluctuations exceeding the expectation from stochastic variation. These results imply that the variation in MHC allele frequencies between cohorts is not a result of demographic events, but rather an effect of selection favouring different MHC alleles in different years.     

Genomic‐scale comparison of sequence‐ and structure‐based methods of function prediction: Does structure provide additional insight?

A function annotation method using the sequence-to-structure-to-function paradigm is applied to the identification of all disulfide oxidoreductases in the Saccharomyces cerevisiae genome. The method identifies 27 sequences as potential disulfide oxidoreductases. All previously known thioredoxins, glutaredoxins, and disulfide isomerases are correctly identified. Three of the 27 predictions are probable false-positives. Three novel predictions, which subsequently have been experimentally validated, are presented. Two additional novel predictions suggest a disulfide oxidoreductase regulatory mechanism for two subunits (OST3 and OST6) of the yeast oligosaccharyltransferase complex. Based on homology, this prediction can be extended to a potential tumor suppressor gene, N33, in humans, whose biochemical function was not previously known. Attempts to obtain a folded, active N33 construct to test the prediction were unsuccessful. The results show that structure prediction coupled with biochemically relevant structural motifs is a powerful method for the function annotation of genome sequences and can provide more detailed, robust predictions than function prediction methods that rely on sequence comparison alone.     

Non‐native conditions favor non‐native populations of invasive plant: demographic consequences of seed size variation?

Trait differences between native and non‐native populations may explain the greater abundance and impact of some organisms in their non‐native ranges than in their native ranges. Here, we conducted reciprocal common gardens in southwestern Turkey (home) and central Argentina (away) to explore the hypothesis that the greater success of the invasive ruderal Centaurea solstitialis in Argentina than Turkey is partially explained by differences between home and away populations. Unusual among common gardens, our experimental design included seed additions to explicitly evaluate population level responses, as well as disturbance and no‐disturbance treatments. We documented seed mass in native and non‐native populations, and during the experiment, we periodically measured density, plant size, and herbivory. After six months, we determined the establishment of plants for populations from both origins in both home and away common gardens. Seed mass was two times larger for Argentinean than Turkish populations. Density, plant size and final establishment were also greater for plants from Argentinean than from Turkish populations, but only in the common garden in Argentina. In Turkey, no differences between population origins were detected for these variables. Herbivory was similar for populations from both origins in both common gardens. As expected, disturbance generally increased plant performance in both regions. Our results suggest that increased seed size in non‐native populations may have demographic consequences under non‐native conditions that can contribute to the invasive success of C. solstitialis. This is the first reciprocal common garden that supports the idea that seed size variation contributes to demographic differences for an invasive species between native and non‐native distributions, but our findings further suggest that seed size effects on demography depend on the ecological context in which population processes occur.     

Morphological anti‐predator defences in the nine‐spined stickleback: constitutive,induced or both?

Environmental differences among populations are expected to lead to local adaptation, while spatial or temporal environmental variation within a population will favour evolution of phenotypic plasticity. As plasticity itself can be under selection, locally adapted populations can vary in levels of plasticity. Nine‐spined stickleback (Pungitius pungitius) originating from isolated ponds (low piscine predation risk, high competition) vs. lake and marine populations (high piscine predation risk, low competition) are known to be morphologically adapted to their respective environments. However, nothing is known about their ability to express phenotypic plasticity in morphology in response to perceived predation risk or food availability/competition. We studied predator‐induced phenotypic plasticity in body shape and armour of marine and pond nine‐spined stickleback in a factorial common garden experiment with two predator treatments (present vs. absent) and two feeding regimes (low vs. high). The predation treatment did not induce any morphological shifts in fish from either habitat or food regime. However, strong habitat‐dependent differences between populations as well as strong sexual dimorphism in both body shape and armour were found. The lack of predator‐induced plasticity in development of the defence traits (viz. body armour and body depth) suggests that morphological anti‐predator traits in nine‐spined stickleback are strictly constitutive, rather than inducible. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

What is the function of neuronal AP‐3?

Neurotransmission requires the proper organization and rapid recycling of synaptic vesicles. Rapid retrieval has been suggested to occur either by kiss-and-stay or kiss-and-run mechanisms, whereas classical recycling is mediated by clathrin-dependent endocytosis. Molecular coats are key components in the selection of cargos, AP-2 (adaptor protein 2) playing a prominent role in synaptic vesicle endocytosis. Another coat protein, AP-3, has been implicated in synaptic vesicle biogenesis and in the generation of secretory and lysosomal-related organelles. In the present review, we will particularly focus on the recent data concerning the recycling of synaptic vesicles and the function of AP-3 and the v-SNARE (vesicular soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) TI-VAMP (tetanus neurotoxin-insensitive vesicle-associated membrane protein) in these processes. We propose that AP-3 plays an important regulatory role in neurons which contributes to the basal and stimulated exocytosis of synaptic vesicles.     

Degradation of fibrin-β amyloid co-aggregate: A novel function attributed to ubiquitin

Human placental extract contains numerous bioactive components that are effective wound healing, antimicrobial and anti-inflammatory agents. During our investigation on the therapeutic potency of human placental extract, we have purified ubiquitin-like molecules that showed strong fibrino(geno)lytic activity. Further investigation confirmed similar potency of ubiquitin purified from adult human erythrocyte. Additionally, ubiquitin efficiently degraded disordered amyloid β 42 peptide (Aβ42) aggregate and fibrin-Aβ42 co-aggregate in vitro and reduced co-aggregate induced cytotoxicity in SH-SY5Y human neuroblastoma cells as compared to plasmin. Ubiquitin also degraded abnormal co-aggregates of fibrin with other plasma proteins such as fibronectin, albumin, lysozyme, tranthyretin and α-synuclein. To elucidate the mechanism of degradation, synthetic peptides (ADG, GKT, DQQ, QRL, LIF, AGK, HLVL) derived from ubiquitin template as well as synthetic ubiquitin (8565.32?Da) were employed. Synthetic ubiquitin completely degraded preformed Aβ 42 aggregate and fibrin-Aβ42 co-aggregate, whereas, the smaller synthetic peptides showed varying degrees of degradation. These observations attribute a novel function of ubiquitin that may be used for degrading abnormal fibrin clots in human body. Thorough investigation might unfold a novel molecular mechanism of ubiquitin in protein homeostasis.     

Do Insectivorous Birds use Volatile Organic Compounds from Plants as Olfactory Foraging Cues? Three Experimental Tests

Some insectivorous birds orient towards insect‐defoliated trees even when they do not see the foliar damage or the herbivores. There are, however, only a few studies that have examined the mechanisms behind this foraging behaviour. Previous studies suggest that birds can use olfactory foraging cues (e.g. volatile organic compounds (VOCs) emitted by defoliated plants), indirect visual cues or a combination of the two sensory cues. VOCs from insect‐defoliated plants are known to attract natural enemies of herbivores, and researchers have hypothesized that VOCs could also act as olfactory foraging cues for birds. We conducted three experiments across a range of spatial scales to test this hypothesis. In each experiment, birds were presented with olfactory cues and their behavioural responses or foraging outcomes were observed. In the first experiment, two different VOC blends, designed to simulate the volatile emissions of mountain birch (Betula pubescens ssp. czerepanovii) after defoliation by autumnal moth (Epirrita autumnata) larvae, were used in behavioural experiments in aviaries with pied flycatchers (Ficedula hypoleuca). The second experiment was a field‐based trial of bird foraging efficiency; the same VOC blends were applied to mountain birches, silver birches (B. pendula) and European white birches (B. pubescens) with plasticine larvae attached to the trees to serve as artificial prey for birds and provide a means to monitor predation rate. In the third experiment, the attractiveness of silver birch saplings defoliated by autumnal moth larvae versus intact controls was tested with great tits (Parus major) and blue tits (Cyanistes caeruleus) in an aviary. Birds did not orient towards either artificial or real trees with VOC supplements or towards herbivore‐damaged saplings when these saplings and undamaged alternatives were hidden from view. These findings do not support the hypothesis that olfactory foraging cues are necessary in the attraction of birds to herbivore‐damaged trees.     

The cabbage aphid: a walking mustard oil bomb

The cabbage aphid, Brevicoryne brassicae, has developed a chemical defence system that exploits and mimics that of its host plants, involving sequestration of the major plant secondary metabolites (glucosinolates). Like its host plants, the aphid produces a myrosinase (beta-thioglucoside glucohydrolase) to catalyse the hydrolysis of glucosinolates, yielding biologically active products. Here, we demonstrate that aphid myrosinase expression in head/thoracic muscle starts during embryonic development and protein levels continue to accumulate after the nymphs are born. However, aphids are entirely dependent on the host plant for the glucosinolate substrate, which they store in the haemolymph. Uptake of a glucosinolate (sinigrin) was investigated when aphids fed on plants or an in vitro system and followed a different developmental pattern in winged and wingless aphid morphs. In nymphs of the wingless aphid morph, glucosinolate level continued to increase throughout the development to the adult stage, but the quantity in nymphs of the winged form peaked before eclosion (at day 7) and subsequently declined. Winged aphids excreted significantly higher amounts of glucosinolate in the honeydew when compared with wingless aphids, suggesting regulated transport across the gut. The higher level of sinigrin in wingless aphids had a significant negative impact on survival of a ladybird predator. Larvae of Adalia bipunctata were unable to survive when fed adult wingless aphids from a 1% sinigrin diet, but survived successfully when fed aphids from a glucosinolate-free diet (wingless or winged), or winged aphids from 1% sinigrin. The apparent lack of an effective chemical defence system in adult winged aphids possibly reflects their energetic investment in flight as an alternative predator avoidance mechanism.     

Low light reflectance may explain the attraction of birds to defoliated trees

Plants use volatile organic compounds to attract invertebratepredators and parasitoids of their herbivore pests. Recently,it has been suggested that plants, either through visual orolfactory cues, may also "cry for help" from vertebrate predatorssuch as birds. We show that in a laboratory choice test, passerinebirds (Parus major and Cyanistes caeruleus) were attracted tothe intact branches of trees (Betula pendula) suffering fromfoliar damage caused by herbivore larvae (Epirrita autumnata)in nontest branches. Species, age, or sex of the experimentalbird or lighting (ultraviolet [UV] or non-UV) did not affectthe preference. However, the birds made a clear choice betweenthe treatments when the trees came from a forest patch receivingmore sunlight, whereas no obvious choice was observed when thetrees came from a shadier forest patch. Results of the choicetest were supported by the spectral reflectance of tree leaves.In the sunnier forest patch, control trees reflected more visiblelight than the herbivore trees, whereas no such difference wasfound in the shadier forest patch trees. We suggest that avianpredators use their vision within visible wavelengths to findinsect-rich plants even when they do not see the prey itemsor damaged leaves.     

Ant associations in the Neotropical shrub Turnera subulata (Turneraceae): Costs or benefits to the host plant?

The results of ecological interactions depend on the costs and benefits involved in different ecological contexts. Turnera subulata is a shrubby plant with extrafloral nectaries that are associated with ants. Here, we test the hypotheses that the association between T. subulata and ants results in: (i) positive effects on host plant growth and reproduction; (ii) plant herbivory reduction and (iii) inhibition of the host plant visitation by beneficial organisms. Thirty experimental plots were established in northeastern Brazil, either in association with ants or without ants (N = 15 plots/treatment), with four plants each (total 120 plants). Vegetative growth (plant height and number of leaves), reproductive investment (flowers and fruits), herbivory rates and numbers of beneficial visitors were quantified during all phenological stages of the host plant. Data were analysed using generalized linear mixed models. At the host plant maturation stage, we found a trade‐off between growth and reproduction. Plants with ants had lower mean height; however, they invested more in reproduction (a higher number of flowers and fruits) compared to plants without ants. During the flowering stage, the abundance of sucking herbivores was higher in plots without ants but chewing herbivore abundance increased in the maturation stage in plots with ants. The cumulative proportion of leaves with herbivore damage did not differ between treatments, and the presence of ants reduced the number of beneficial visitors (e.g. pollinators and natural enemies) to the host plants. Our results show that association with ants results in some costs for the host plant, however, these costs appear to be offset by the defensive role of ants, which favours plant reproductive investment. In general, our results help to elucidate mechanisms involved in trophic interactions within the complex network of interactions involving ants and plants.