Do plants use airborne cues to recognize herbivores on their neighbours?

Plants show defensive responses after exposure to volatiles from neighbouring plants infested by herbivores. When a plant’s neighbours host only species of herbivores that do not feed on the plant itself, the plant can conserve energy by maintaining a low defence level. An intriguing question is whether plants respond differently to volatiles from plants infested by herbivores that pose greater or lesser degrees of danger. We examined the secretion of extrafloral nectar (EFN) in lima bean plants exposed to volatiles from cabbage plants infested by common cutworm, two-spotted spider mites, or diamondback moth larvae. Although the first two herbivore species feed on lima bean plants, diamondback moth larvae do not. As a control, lima bean plants were exposed to volatiles from uninfested cabbage plants. Only when exposed to volatiles from cabbage plants infested by spider mites did lima bean plants significantly increase their EFN secretion compared with the control. Increased EFN secretion can function as an indirect defence by supplying the natural enemies of herbivores with an alternative food source. Of the three herbivore species, spider mites were the most likely to move from cabbage plants to lima bean plants and presumably posed the greatest threat. Although chemical analyses showed differences among treatments in volatiles produced by herbivore-infested cabbage plants, which compounds or blends triggered the increased secretion of EFN by lima bean plants remains unclear. Thus, our results show that plants may tune their defence levels according to herbivore risk level.     

Does universal temperature dependence apply to communities? An experimental test using natural marine plankton assemblages

The metabolic theory of ecology (MTE) is an intriguing but controversial theory that tries to explain ecological patterns at all scales on the basis of first principles. Temperature plays a pivotal role in this theory. According to MTE, the Arrhenius relationship that describes the effect of temperature on biochemical reactions extends to a 'universal temperature dependence' that encompasses all kinds of processes and scales up to the cellular, the organismal, and the community level. In this study we test the prediction that community growth rate is temperature dependent in an Arrhenius-like way. First, we performed a literature review of the scanty data on the temperature dependence of the rates of metabolism, photosynthesis and growth of communities. In contrast to the predictions of MTE, the community activation energies did not cluster around 0.32 eV, the activation energy of photosynthesis and primary production or around 0.65 eV, the activation energy of metabolism. However, in none of the published studies the conditions were sufficiently controlled to allow firm conclusions. We therefore also performed replicated and controlled experiments using natural assemblages of marine plankton. As predicted by MTE, the maximal growth rates of community biomass increased linearly in an Arrhenius plot, with a slope close to 0.32 eV. However, a diversity of other models for the temperature dependence of community growth rates fit our data equally well. Hence, our results are at best a weak confirmation of MTE.     

Do trace metals select for darker birds in urban areas? An experimental exposure to lead and zinc

Trace metals from anthropogenic activities are involved in numerous health impairments and may therefore select for detoxification mechanisms or a higher tolerance. Melanin, responsible for the black and red colourations of teguments, plays a role in metal ion chelation and its synthesis is positively linked to immunity, antioxidant capacity and stress resistance due to pleiotropic effects. Therefore, we expected darker birds to (1) store higher amounts of metals in their feathers, (2) maintain lower metal concentrations in blood and (3) suffer less from metal exposure. We exposed feral pigeons (Columba livia) exhibiting various plumage darkness levels to low, but chronic, concentrations of zinc and/or lead, two of the most abundant metals in urban areas. First, we found negative and positive effects of lead and zinc, respectively, on birds' condition and reproductive parameters. Then, we observed positive relationships between plumage darkness and both zinc and lead concentrations in feathers. Interestingly, though darker adults did not maintain lower metal concentrations in blood and did not have higher fitness parameters, darker juveniles exhibited a higher survival rate than paler ones when exposed to lead. Our results show that melanin‐based plumage colouration does modulate lead effects on birds' fitness parameters but that the relationship between metals, melanin, and fitness is more complex than expected and thus stress the need for more studies.     

Do carotenoids buffer testosterone-induced immunosuppression? An experimental test in a colourful songbird

Testosterone (T) is hypothesized to be an important honesty reinforcer of animal sexual signals. Owing to its immunosuppressive effects, only those individuals that can immunologically withstand high T levels can develop the most exaggerated traits. To date, few studies have isolated phenotypic or genotypic buffers that provide 'high-quality' animals with such an advantage. Dietary carotenoid pigments may in fact confer such a benefit because when in high supply carotenoids boost immunocompetence and coloration in animals like birds and fishes. We examined the experimental effect of T elevation on carotenoid and immune status in male and female zebra finches (Taeniopygia guttata) and found that T was immunostimulatory in a generalized cell-mediated challenge. We also detected a significant interaction between T treatment and the change in plasma carotenoids that occurred during the immune challenge; the relationship between blood carotenoid change and immunity was positive in controls and negative in T-implanted birds. This suggests that, while correlationally birds with high carotenoid stores were inherently better at mounting strong immune responses, experimentally administered T induced birds to deplete carotenoids for maximizing their health. Our findings highlight a nutrient-specific mechanism by which animals escape high immune costs of T elevation and thus can still elevate ornamentation.     

How does metabolic rate scale with egg size? An experimental test with sea urchin embryos

The consequences of changes in egg size for the development of marine invertebrates have been the subject of much theoretical and experimental work. Models that explore larval developmental modes in the context of maternal investment per offspring are often couched in an energetic framework, but the relationships between egg size and the energetics of larval development are poorly understood. We used blastomere separations to examine how experimental reductions in egg size affected (1) larval metabolic rate and (2) larval resistance to starvation. We found that separating blastomeres at the 2- and 4-cell stage resulted in average reductions of 50% and 75%, respectively, in larval metabolic rate. This suggests that, in an experimental context, mass-specific metabolic rate does not change with egg size. We also found that a 50% reduction in egg volume did not reduce the resistance of larvae to starvation when particulate food was withheld. This suggests that the material supplied to larvae in the egg is used primarily for construction of the larval body, rather than as a buffer against starvation or as a means of reducing reliance on exogenous fuel to sustain maintenance metabolism.     

Frequency distribution of egg mass of passerine and non-passerine birds based on Sch?nwetter's tables

Summary Frequency distributions of egg mass for more than 3000 species each of passerine and non-passerine birds derived from the tables ofSchönwetter are lognormal in form.

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Häufigkeitsverteilung der Eimassen nach den Angaben in den Tabellen vonSchönwetter

Zusammenfassung Die Häufigkeiten der Eimassen von jeweils über 3000 Arten der Singvögel und Nichtsingvögel aus den Tabellen im Handbuch vonSchönwetter sind lognormal verteilt (vgl. Abb.).

     

Do spatial patterns of clonal fragments and architectural responses to defoliation depend on the structural blue-print? An experimental test with two rhizomatous Cyperaceae

Clonal architecture is involved in performance of clonal fragments, as it determines spatial distribution of ramets. It is expected to rely on the species-specific expression of several architectural traits (structural blue-print). However, in contrasting environments, realized clonal architectures may differ, due to phenotypic plasticity. In this paper, we compared clonal architectures between two rhizomatous ecologically close Cyperaceae (Carex divisa and Eleocharis palustris) in non-defoliated and defoliated conditions. Two questions were addressed. (1) How much do the structural blue-print and resulting colonization and occupation of space differ between both species? (2) Does the structural blue-print constrain plastic responses of clonal architecture to defoliation? Traits related to performance, spatial pattern, architecture and biomass allocation of clonal fragments were monitored through an original non-destructive mapping method. In non-defoliated conditions, both species showed similar biomass but contrasting architectures and patterns of biomass allocation to rhizomes that resulted in different spatial patterns. The rhizome network of C. divisa, which consisted in only two primary rhizomes but several branches, was involved in resource storage rather than in spatial colonization. Conversely, E. palustris produced on average six primary rhizomes that grew in the whole horizontal plane, maximizing both occupation and colonization of space. These differences in structural constraints coupled with allometric relationships, resulted in differential responses to defoliation. In C. divisa, the costs associated to defoliation caused a decrease in branching, limiting the area occupied and number of ramets produced by clonal fragments, but increasing ramet density. Conversely, the weakly branched rhizome network of E. palustris was not affected by defoliation. Both spatial strategies (consolidation vs. colonization) are likely to provide ecological advantages allowing their coexistence in grazed meadows.     

Do female tamarins use visual cues to detect fruit rewards more successfully than do males?

Primates are unique among eutherian mammals for possessing trichromatic colour vision. It is generally proposed that trichromacy evolved to aid detection of ripe fruits against mature foliage. However, while trichromacy is routine in all Old World monkeys and apes (the catarrhines), a cone opsin polymorphism in New World monkeys (the platyrrhines) results in foraging groups with mixed capacities for chromatic distinction. Although 50-66% of female platyrrhines are trichromatic, all males are dichromatic. Here, we test the hypothesis that trichromatic platyrrhines use visual cues to detect fruit rewards more successfully than do males. Specifically, we ask whether female emperor tamarins, Saguinus imperator imperator, and saddleback tamarins, S. fuscicollis weddelli, are the first members of their foraging group to locate food patches; and, furthermore, whether they are more successful than males in using colour, shape and size cues to discriminate between sham and reward feeding sites. Our results show that females and males do not differ in their ability to locate or discriminate between feeding sites. We conclude that trichromatic vision in female tamarins does not confer an advantage for detecting yellow fruit rewards against mature foliage. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Does attraction to conspecifics explain the patch‐size effect? An experimental test

Recent theory suggests that attraction to conspecifics during habitat selection can be one potential, yet untested, mechanism for animal sensitivity to habitat fragmentation. The least flycatcher Empidonax minimus , a highly territorial migratory bird, has previously been shown to be attracted to conspecifics and sensitive to patch size by avoiding small patches of riparian forest in Montana, USA. I used a large-scale field experiment in this region to test the conspecific attraction hypothesis for explaining sensitivity to patch size, and I supplemented this experiment by estimating whether vegetation structure, nest predation, or nest parasitism rates could better explain patterns of sensitivity to patch size. Vegetation structure did not vary consistently with patch size, based on a random sample of patches across 150  km of the Madison and Missouri Rivers, Montana. Nest predation and parasitism rates by brown-headed cowbirds Molothrus ater also did not vary with patch size during the experiment. However, when conspecific cues were simulated across a gradient of patch sizes, flycatchers settled in all patches – and their sensitivity to patch size vanished – providing strong support for the conspecific attraction hypothesis. These results provide the first experimental evidence that attraction to conspecifics can indeed help explain area sensitivity in nature and highlight how understanding the role of animal behavior in heterogeneous landscapes can aid in interpreting pressing conservation issues.     

Trichomes as dangerous lollipops: Do lizards also use caterpillar body and frass odor to optimize their foraging?

When attacked by herbivores, plants produce toxic secondary metabolites that function as direct defenses, as well as indirect defenses that attract and reward predators of the offending herbivores. These indirect defenses include both nutritive rewards such as extra floral nectar, as well as informational rewards, such as the production and release of volatile compounds that betray the location of feeding herbivores to predators. Herbivory of Nicotiana attenuata by the tobacco hornworm (Manduca larvae) alters the volatile profiles of both the plant and larval headspace. Herbivory-elicited specific changes in the volatile profiles are detected by arthropod predators of Manduca larvae. The known predators that perceive volatile cues induced by Manduca herbivory of N. attenuata are insects that target Manduca at early developmental stages, when the larvae are still small; large, late-instar larvae may have outgrown these predation risks. However, here we offer evidence that branched chain aliphatic acids derived from the digestion of plant O-acyl sugars from trichomes may betray Manduca larvae to lizard predators during late developmental stages as well.     

Adaptation or exaptation? An experimental test of hypotheses on the origin of salinity tolerance in Bufo calamita

The natterjack toad (Bufo calamita) shows variation in embryonic and larval salinity tolerance across populations in southern Spain. However, its aquatic/terrestrial biphasic life cycle, together with remarkable differences in salinity tolerance between Spanish and UK freshwater populations suggest an alternative hypothesis to local adaptation. Drought resistance during the terrestrial phase and salinity tolerance during the aquatic phase are both related to osmotic stress tolerance, and if there were an association between them, one could have evolved as an exaptation from the other. To test such an association, we reared B. calamita juveniles from three populations known to differ genetically in their salinity tolerance, under either dry or humid conditions. Drought decreased growth rate, enhanced burying behaviour, and decreased foraging activity and efficiency. No significant population x treatment interaction was found for any variable, i.e. populations were equally affected by drought. These results do not support the hypothesis of a genetic association between salinity and drought tolerance.     

Can plants evolve tolerance mechanisms to heterospecific pollen effects? An experimental test of the adaptive potential in Clarkia species

Flowering plants do not occur alone and often grow in mixed‐species communities where pollinator sharing is high and interactions via pollinators can occur at pre‐ and post‐pollination stages. While the causes and consequences of pre‐pollination interactions have been well studied little is known about post‐pollination interactions via heterospecific pollen (HP) receipt, and even less about the evolutionary implications of these interactions. In particular, the degree to which plants can evolve tolerance mechanisms to the negative effects of HP receipt has received little attention. Here, we aim to fill this gap in our understanding of post‐pollination interactions by experimentally testing whether two co‐flowering Clarkia species can evolve HP tolerance, and whether tolerance to specific HP ‘genotypes’ (fine‐scale local adaptation to HP) occurs. We find that Clarkia species vary in their tolerance to HP effects. Furthermore, conspecific pollen performance and the magnitude of HP effects were related to the recipient's history of exposure to HP in C. xantiana but not in C. speciosa. Specifically, better conspecific pollen performance and smaller HP effects were observed in populations of C. xantiana plants with previous exposure to HP compared to populations without such exposure. These results suggest that plants may have the potential to evolve tolerance mechanisms to HP effects but that these may occur not from the female (stigma, style) but from the male (pollen) perspective, a possibility that is often overlooked. We find no evidence for fine‐scale local adaptation to HP receipt. Studies that evaluate the adaptive potential of plants to the negative effects of HP receipt are an important first step in understanding the evolutionary consequences of plant–plant post‐pollination interactions. Such knowledge is in turn crucial for deciphering the role of plant–pollinator interactions in driving floral evolution and the composition of co‐flowering communities.     

The use of flavonoid aglycones in in vitro systems to test biological activities: based on bioavailability data,is this a valid approach?

The majority of in vitro assays on biological activities of flavonoids have used the aglycone form as the test compound. This form is readily available from commercial sources and comparable approaches have been used for testing efficacy of drugs. This paper presents the hypothesis that aglycones are only transiently present in vivo at significant concentrations at specific sites. The pathway of metabolism of flavonoids in mammals in vivo, focusing on aglycone formation, is examined to facilitate better design in the future of in vitro cell culture experiments. In vitro experiments using flavonoids and cultured cells require careful consideration of absorption and bioavailability for their appropriate interpretation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Do homoiologies impede phylogenetic analyses of the fossil hominids? An assessment based on extant papionin craniodental morphology

Homoiologies are phylogenetically misleading resemblances among taxa that can be attributed to phenotypic plasticity. Recently, it has been claimed that homoiologies are widespread in the hominid skull, especially in those regions affected by mastication-related strain, and that their prevalence is a major reason why researchers have so far been unable to obtain a reliable estimate of hominid phylogeny. To evaluate this "homoiology hypothesis", we carried out analyses of a group of extant primates for which a robust molecular phylogeny is available-the papionins. We compiled a craniometric dataset from measurements that differ in their susceptibility to mastication-related strain according to developmental considerations and experimental evidence. We used the coefficient of variation and analysis of variance with post hoc least significant difference comparisons in order to evaluate the variability of the measurements. The prediction from the homoiology hypothesis was that dental measurements, which do not remodel in response to strain, should be less variable than low-to-moderate-strain measurements, and that the latter should be less variable than high-strain measurements. We then performed phylogenetic analyses using characters derived from the measurements and compared the resulting phylogenetic hypotheses to the group's consensus molecular phylogeny. The prediction was that, if the homoiology hypothesis is correct, the agreement between the craniometric and molecular phylogenies would be best in the analyses of dental characters, intermediate in the analyses of low-to-moderate-strain characters, and least in the analyses of high-strain characters. The results of this study support the suggestion that mastication-related mechanical loading can result in variation in hominid cranial characters. However, they do not support the hypothesis that homoiology is a major reason why phylogenetic analyses of hominid crania have so far yielded conflicting and weakly supported hypotheses of relationship. These findings are consistent with a recent test of the homoiology hypothesis using craniodental data from extant hominoids, and cast doubt on the validity of the homoiology hypothesis, as originally formulated.     

How does gene expression level contribute to thermophilic adaptation of prokaryotes? An exploration based on predictors

By analyzing the predicted gene expression levels of 33 prokaryotes with living temperature span from <10 degrees C to >100 degrees C, a universal positive correlation was found between the percentage of predicted highly expressed genes and the organisms' optimal growth temperature. A physical interpretation of the correlation revealed that highly expressed genes are statistically more thermostable than lowly expressed genes. These findings show the possibility of the significant contribution of gene expression level to the prokaryotic thermal adaptation and provide evidence for the translational selection pressure on the thermostability of natural proteins during evolution.     

Are there any differences between taxa groups having distinct ecological traits based on their responses to environmental factors?

The aim of this study was to explore the differences between taxa groups with different ecological strategies for persistence, regarding their responses to environmental factors and seasonal variation. We studied the relationship between the seasonal patterns and habitat attributes of the Ephemeroptera, Plecoptera, Trichoptera (EPT) and the Colepotera, Heteroptera (CH) assemblages. Sampling was carried out in May, July and October of 2009. Samples were taken according to the AQEM protocol at 10 stream sections in the Mecsek Mountains. Based on multivariate analyses (RDA, pRDA), distinctive differences were found between the EPT and the CH taxa groups regarding their response to local chemical variables and variables describing the riparian vegetation. The measured environmental variables had a higher relative influence on the distribution patterns of EPT and CH assemblages than spatial variation of species patterns. The physical structure of aquatic habitats, including the type of bedrock, had greater effects on CH than EPT patterns, whereas the structure of riparian vegetation was more important for EPT than CH. Average density and average taxon richness of EPT were seasonally variable, but CH assemblages were not.     

Do predators have a role to play in wetland ecosystem functioning? An experimental study in New England salt marshes

The historical ecological paradigm of wetland ecosystems emphasized the role of physical or “bottom‐up” factors in maintaining functions and services. However, recent studies have shown that the loss of predators in coastal salt marshes can lead to a significant reduction in wetland extent due to overgrazing of vegetation by herbivores. Such studies indicate that consumers or “top‐down” factors may play a much larger role in the maintenance of wetland ecosystems than was previously thought. The objective of this study was to evaluate whether altering top‐down control by manipulating the presence of predators can lead to measurable changes in salt marsh ecosystem properties. Between May and August of 2015 and 2016, we established exclosure and enclosure cages within three New England coastal wetland areas and manipulated the presence of green crab predators to assess how they and their fiddler and purple marsh crab prey affect changes in ecosystem properties. Predator presence was associated with changes in soil nitrogen and aboveground biomass at two of the three field sites, though the magnitude and direction of these effects varied from site to site. Further, path analysis results indicate that across field sites, a combination of bottom‐up and top‐down factors influenced changes in measured variables. These results challenge the growing consensus that consumers have strong effects, indicating instead that predator impacts may be highly context‐dependent.     

Are soil biota buffered against climatic extremes? An experimental test on testate amoebae in arctic tundra (Qeqertarsuaq,West Greenland)

Climate warming is likely to have pronounced impacts on soil biota in arctic ecosystems. In a warmer climate, heatwaves are more frequent and intense, but it is unclear to what extent soil communities are buffered against this. We studied the effects of an artificially induced heatwave on the structure of testate amoebae communities in dry heath tundra in Qeqertarsuaq (Disko Island, West Greenland) during the summer of 2003. While the heatwave was severe enough to induce significant leaf mortality in the aboveground vegetation, overall testate amoebae abundance did not react to the difference in temperature. However, in the heated plots transient shifts in species populations occurred during the exposure, followed by increases in species richness weeks after the heatwave had ended. The most important taxa appearing after the heating period belonged to bacterivorous genera, in agreement with a transient peak in bacterial colony forming units, caused by the heatwave. Lobose testate amoebae resisted the heating and its associated desiccation better than their filose counterparts.     

Do tree species characteristics influence soil respiration in tropical forests? A test based on 16 tree species planted in monospecific plots

The high spatial variability of soil respiration in tropical rainforests is well evaluated, but influences of biotic factors are not clearly understood. This study underlines the influence of tree species characteristics on soil respiration across a 16-monospecific plot design in a tropical plantation of French Guiana. A large variability of soil CO₂ fluxes was observed among plots (i.e. 2.8 to 6.8 μmol m^?2 s^?1) with the ranking being constant across seasons. There were no significant relationships between soil respiration and soil moisture or soil temperature, neither spatially, nor seasonally. The variability of soil respiration was mainly explained by quantitative factors such as leaf litterfall and basal area. Surprisingly, no significant relationship was observed between soil respiration and root biomass. However, the influence of substrate quality was revealed by a strong relationship between soil respiration and litterfall P (and litterfall N, to a lesser extent).