Direct and indirect interactions with vegetation shape crocodylian ecology at multiple scales

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Direct and indirect interactions involving ants, insect herbivores, parasitoids, and the host plant Baccharis dracunculifolia (Asteraceae)

Abstract.  1. The relative importance of direct and indirect interactions in controlling organism abundance is still an unresolved question. This study investigated the role of the direct and indirect interactions involving ants, aphids, parasitoids, and the host plant Baccharis dracunculifolia (Asteraceae) on a galling herbivore Baccharopelma dracunculifoliae (Homoptera: Psyllidae).
2. The effects of these interactions on the galling herbivore's performance were evaluated by an exclusion experiment during two consecutive generations of the galling insect.
3. Ants had a direct negative effect on the performance of the galling herbivore by reducing the number of nymphs per gall. In contrast, ants had no indirect effects on gall mortality through the associated parasitoids.
4. Aphids negatively affected gall development, suggesting that galls and aphids might be partitioning photoassimilates and nutrients moving throughout host-plant tissues.
5. In addition, galls that developed during the rainy season were heavier, indicating that variation in the host plant, due to weather changes, can affect the development of B. dracunculifoliae galls. However, variation in the development of B. dracunculifoliae galls due to presence of aphids or the weather changes did not affect parasitoid attack.
6. These results suggest that direct interactions between ants and galls influenced galling insect abundance, whereas numerical indirect effects involving galling insects, ants, aphids, and host plants were less conspicuous.     

Asymmetric interactions between plants and seed-harvesting ants in a Mediterranean pasture

A four-year study on the interactions between plants and seed-harvesting ants in a Mediterranean pasture is reviewed in this paper. As previously reported in many studies on plant–herbivore interactions, ant–plant relationships are also asymmetric; plants had a larger impact on herbivore dynamics than vice versa. However, the asymmetry did not refer to population dynamics but rather to animal foraging strategies. Ants did not exert a significant influence on vegetation dynamics in terms of plant abundance. The main constraints underlying vegetation change were self-regulation and rainfall. In contrast, the structural characteristics and abundance of vegetation had a significant impact on several important features of food harvesting by ants. This influence was not only associated with their feeding requirements but also with their foraging activities.     

植物与植食性昆虫的分子互作:基础与应用

植物与植食性昆虫之间存在着复杂的分子互作.首先,植食性昆虫会利用自身的嗅觉和味觉化学感觉系统,通过对植物挥发性和非挥发性信息化合物的编码与解析,结合对植物颜色、形状等物理信息的感觉与编码,定位及确定寄主植物.其次,植物可以通过位于细胞膜的受体识别植食性昆虫相关模式分子和损伤相关模式分子,启动由早期信号事件和植物激素信号...     

The interaction between the coastal brown ant,Pheidole megacephala (Fabricius), and other invertebrate fauna of Mt Coot-tha (Brisbane,Australia)

Abstract Sampling of invertebrate fauna was carried out on Mt Coot-tha, between 25 February and 11 March 1992, to determine whether the presence of the coastal brown ant, Pheidole megacephala (Fabricius), affected die abundance and diversity of other invertebrates. Four plots were sampled; in two the coastal brown ant was present and in two it was absent. The overall abundance of invertebrates did not differ significantly between plots. The abundance of Collembola did vary significantly, but intraplot variability was large. Mite numbers did not differ significantly between plots, except for the family Laelapidae. Abundance of other ant species did not differ significantly between plots, but there was a difference in species composition; Dolichoderinae and Ponerinae were absent or poorly represented in plots where the coastal brown ant was present.     

Direct and indirect species interactions influencing within-season dynamics of apple rust mite, Aculus schlechtendali (Acari: Eriophyidae)

We conducted a series of path analyses to determine which direct and indirect species interactions were most important in determining the within-season dynamics of apple rust mite (Aculus schlechtendali) (Eriophyidae) in a series of Nova Scotian (Canada) apple orchards. Typhlodromus pyri (Phytoseiidae) was usually more important than Zetzellia mali (Stigmaeidae) in the direct reduction of the apple rust mite population growth rate. When both predators contributed to lowering apple rust mite growth, T. pyri acted earlier in the season than did Z. mali. Predation by T. pyri was not affected by plant quality (nitrogen content or cultivar), but predation by Z. mali was enhanced by high nitrogen levels and was influenced by cultivar. There was little evidence of direct competition between Panonychus ulmi and apple rust mite in these orchards, possibly due to the low densities of P. ulmi. The indirect effects were generally smaller than the direct effects, but were occasionally important. Apparent competition between P. ulmi and apple rust mite was observed at times in some orchards, more often mediated by Z. mali than by T. pyri. Interference between the predator species was only occasionally strong enough to affect apple rust mite population dynamics.     

Direct and indirect interactions in the recognition between a cross‐neutralizing antibody and the four serotypes of dengue virus

Dengue fever is the most important vector‐borne viral disease. Four serotypes of dengue virus, DENV1 to DENV4, coexist. Secondary infection by a different serotype is a risk factor for severe dengue. Monoclonal antibody mAb4E11 neutralizes the four serotypes of DENV with varying efficacies by recognizing an epitope located within domain‐III (ED3) of the viral envelope (E) protein. To better understand the cross‐reactivities between mAb4E11 and the four serotypes of DENV, we constructed mutations in both Fab4E11 fragment and ED3, and we searched for indirect interactions in the crystal structures of the four complexes. According to the serotype, 7 to 12 interactions are mediated by one water molecule, 1 to 10 by two water molecules, and several of these interactions are conserved between serotypes. Most interfacial water molecules make hydrogen bonds with both antibody and antigen. Some residues or atomic groups are engaged in both direct and water‐mediated interactions. The doubly‐indirect interactions are more numerous in the complex of lowest affinity. The third complementarity determining region of the light chain (L‐CDR3) of mAb4E11 does not contact ED3. The structures and double‐mutant thermodynamic cycles showed that the effects of (hyper)‐mutations in L‐CDR3 on affinity were caused by conformational changes and indirect interactions with ED3 through other CDRs. Exchanges of residues between ED3 serotypes showed that their effects on affinity were context dependent. Thus, conformational changes, structural context, and indirect interactions should be included when studying cross‐reactivity between antibodies and different serotypes of viral antigens for a better design of diagnostics, vaccine, and therapeutic tools against DENV and other Flaviviruses. Copyright © 2014 John Wiley & Sons, Ltd.     

Links between host-plant type and site of feeding as revealed by the evolution of Palaearctic Eriococcidae (Sternorrhyncha: Coccoidea)

This work is an assessment of the biogeographical, taxonomic, biological and phylogenetic knowledge of the poorly defined family Eriococcidae. The study of its geographical diversity shows the richness of the Palearctic fauna on which the present analysis focuses. The numerous systems dealing with the taxonomy of Eriococcidae are detailed, and the specific taxonomical status of the genus Eriococcus, which contains 155 out of the 175 known Palearctic species is reevaluated. The phylogeny of the palaearctic members of the scale insect family Eriococcidae is reconstructed, using 9 genera and 52 species. Three more scale insect species belonging to 3 families were used as outgroups. The cladistic analysis of 130 morphological characters of the adults resulted in 10 most parsimonious trees, placing Eriococcus buxi as the sister-group of all other sampled Eriococcidae. The genera Acanthococcus, Rhizococcus, Greenisca and Anophococcus appear as para- or polyphyletic, but the weakness of most of the clades does not allow to denounce strictly the monophyly of these genera. However, some clades are supported with high confidence, like (Kaweckia + Neokaweckia), (Anophococcus parvispinus(Anophococcus inermis+Greenisca placida) and (Gossyparia spuria+Acanthococcus aceris). Concerning host-plant relationships, the phylogeny supports an evolutionary scenario whereby the ancestor of the family Eriococcidae fed originally on woody plants, and more typically on leaves. The switch observed from Poaceae to other herbaceous plants is correlated to the switch from leaves as preferred site of nutrition to branches and stems. The supported scenario shows another switch, back from other herbs to Poaceae, associated to the choice of leaves as nutrition site.     

Brownian dynamics of interactions between glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mutants and F-actin

Brownian dynamics simulations of computer models of GAPDH mutants interacting with F-actin emphasized the electrostatic nature of such interactions, and confirmed the importance of four previously identified lysine residues on the GAPDH structure in these interactions. Mutants were GAPDH models in which one or more of the previously identified lysines had been replaced with alanine. Simulations showed reduced binding of these mutants to F-actin compared to wild-type GAPDH. Binding was significantly reduced by mutating the four lysines; the specific electrostatic interaction energy of the quadruple mutant was -7.3 +/- 1.0 compared to -11.4 +/- 0.5 kcal/mol for the wild enzyme. The BD simulations also reaffirmed the importance of quaternary structure for GAPDH binding F-actin.     

Direct and indirect genetic effects in life‐history traits of flour beetles (Tribolium castaneum)

Indirect genetic effects (IGEs) are the basis of social interactions among conspecifics, and can affect genetic variation of nonsocial and social traits. We used flour beetles (Tribolium castaneum) of two phenotypically distinguishable populations to estimate genetic (co)variances and the effect of IGEs on three life‐history traits: development time (DT), growth rate (GR), and pupal body mass (BM). We found that GR was strongly affected by social environment with IGEs accounting for 18% of the heritable variation. We also discovered a sex‐specific social effect: male ratio in a group significantly affected both GR and BM; that is, beetles grew larger and faster in male‐biased social environments. Such sex‐specific IGEs have not previously been demonstrated in a nonsocial insect. Our results show that beetles that achieve a higher BM do so via a slower GR in response to social environment. Existing models of evolution in age‐structured or stage‐structured populations do not account for IGEs of social cohorts. It is likely that such IGEs have played a key role in the evolution of developmental plasticity shown by Tenebrionid larvae in response to density. Our results document an important source of genetic variation for GR, often overlooked in life‐history theory.     

Peaceful post-conflict interactions between aggressors and bystanders in captive lowland gorillas (Gorilla gorilla gorilla)

We observed a colony of lowland gorillas in order to assess the occurrence of Peaceful Post-Conflict Interactions between Aggressors and Bystanders (PPIAB). We compared the dynamics of PPIAB with those of Peaceful Post-Conflict Interactions between Victims and Bystanders (PPIVB), which are directed toward victims. We confirmed the occurrence of PPIAB (mean Triadic Contact Tendency: 41.7%+/-16.2% SEM) at frequencies comparable to PPIVB. Immature gorillas were responsible for most PPIAB. PPIAB occurred when the bystander was unrelated to either the aggressor or the victim, and when it was a relative of the aggressor. However, affinitive contact rates were higher in the former case. Unlike PPIVB, PPIAB significantly reduced the likelihood of further aggressions within the group, suggesting that they work at an immediate level. Our data also suggest that bystanders decide when a peaceful contact may be too risky; in fact, neither PPIAB nor PPIVB occurred after high-intensity aggressions.     

Interspecific interactions between wild pygmy chimpanzees (Pan paniscus) and red colobus (Colobus badius)

Interspecific interactions accompanied by physical contacts between wild pygmy chimpanzees (Pan paniscus) and red colobus (Colobus badius) were observed on three occasions at Wamba, Republic of Zaire. In all cases, the red colobus initiated the interactions by approaching the pygmy chimpanzees. Most of the pygmy chimpanzees, which were within 5 m of the red colobus, were juveniles or infants but the adult male pygmy chimpanzees never showed any interest in the red colobus. The red colobus groomed the chimpanzees in two cases, but the latter never groomed the former. No true aggressive interactions were observed between the two species. The lack of any evidence of hunting of red colobus through longitudinal studies of the pygmy chimpanzees of Wamba, together with the present observations, suggests that red colobus are probably not targets of hunting by the pygmy chimpanzees.     

Resource competition assays between the African big‐headed ant,Pheidole megacephala (Fabricius) and the invasive Argentine ant,Linepithema humile (Mayr): mechanisms of inter‐specific displacement

1. The spread of Argentine ants, Linepithema humile (Mayr), in introduced areas is mainly through the displacement of native ant species owing to high inter‐specific competition. In South Africa, L. humile has not established in the climatically suitable eastern and northern escarpments dominated by the African big headed ant, Pheidole megacephala (Fabricius), probably owing to local biotic resistance. 2. Inter‐specific aggression, at the individual and colony level, and competition for a shared resource were evaluated in the laboratory. 3. Aggression between the two ant species was very high in all of the assays. Both species suffered similar mortality rates during one‐on‐one aggression assays, however, during symmetrical group confrontations, L. humile workers showed significantly higher mortality rates than P. megacephala workers. During asymmetrical group confrontations both species killed more of the other ant species when they had numeric advantage. Both ant species located the shared resource at the same time; however, once P. megacephala discovered the bait, they displaced L. humile from the bait through high inter‐specific aggression, thereafter dominating the bait for the remainder of the trial. 4. The results demonstrate the potential of P. megacephala to prevent the establishment and survival of incipient L. humile colonies through enhanced resource competition and high inter‐specific aggression. This is the first study to indicate potential biotic resistance to the spread of L. humile in South Africa.     

Agonistic interactions between invasive green crabs, Carcinus maenas (Linnaeus), and sub-adult American lobsters, Homarus americanus (Milne Edwards)

The invasive green crab, Carcinus maenas, has recently expanded its range into the Southern Gulf of St. Lawrence, where there is potential for substantial niche overlap with juvenile American lobsters, Homarus americanus. We used two experiments to elicit, record and analyze the agonistic interactions of adult green crabs (carapace width of 63-75 mm) and sub-adult (carapace length of 55-70 mm) lobsters. The first experiment gave each animal equal access to a limited food resource. The green crabs were first to the food in significantly more trials, spent a significantly greater proportion of time with the food, and were able to successfully defend the food from attacks by the heavier lobsters. In the second experiment, we allowed the lobsters to gain possession and initiate feeding on the food before releasing the green crabs. In these trials, the lobsters spent significantly more time with the food, and were able to defend the food from the green crabs. The results of both experiments are discussed in the context of game theory. The different behaviour of the crustaceans in the two experiments is consistent with the “bourgeois” strategy in a hawk and dove game simulation. With this strategy, an animal acts like a hawk if in possession of a resource, but acts like a dove if the other animal is in possession of the resource. The fact that the green crabs were able to physically compete with, and in many cases dominate the larger, heavier lobsters supports the potential for competitive impacts of green crabs on sub-adult lobsters.     

Influence of ants (Hymenoptera: Formicidae) on honeydew excretion and escape behaviors in a myrmecophile,dalbulus quinquenotatus (Homoptera: Cicadellidae), and its congeners

Few leafhopper species are known to be ant-attended. Evidence is presented that unequivocally demonstrates that Dalbulus quinquenotatusis a myrmecophile. In a greenhouse study, the behavior of D. quinquenotatusand four Dalbulusspecies not associated with ants was observed in the absence and presence of the pavement ant, Tetramorium caespitum. D. quinquenotatusis readily contacted by tending ants and responds to stroking on the abdomen from ants' antennae by excreting and holding honeydew droplets until droplets are removed by ants. Nonattended Dalbulusspecies avoid contact with ants by walking,jumping, or flying away when approached. D. quinquenotatusexcretes three to six times the volume of honeydew as do two nonattended species, D. maidisand D. gelbus.Droplets of D. quinquenotatusare about 23% larger in diameter and excreted two to four times more frequently than for the other species. D. quinquenotatustakes about 0.15 s to form honeydew droplets on the anal tube, then holds the droplet an average of 0.28 s before expelling it when ants are absent. In the presence of ants, D. quinquenotatusholds the droplet an average of 1.31 s, which gives ants time to harvest the droplet. Nonattended species, however, immediately expel droplets from the anal tube after droplet formation. This ant-leafhopper mutualism apparently has evolved due to the ability of D. quinquenotatusto have extensive physical contact with ants and excrete large amounts of honeydew. D. chiapensis,a possible descendent of D. quinquenotatus,may secondarily have lost its mutualistic relationship with ants.     

Plant phenology and seed predation: interactions between gorses and weevils in Brittany (France)

Exapion ulicis (Forster) and Exapion lemovicinum (Hoffmann) (Coleoptera: Curculionoidea: Apionidae) are seed predators of the three gorse species occurring in Brittany (France): Ulex europaeus L., Ulex gallii Planch., and Ulex minor Roth.(Fabaceae). Host‐plant phenology plays a major role in the relationship between apionid weevils and their gorse species, because larvae develop within gorse pods and adults have to wait for pod dehiscence to be released. We monitored flowering and fruiting phenology of gorse species, weevil reproductive behaviour, and egg‐laying patterns in six natural populations in the native area of these gorse species. At each site, U. europaeus, which flowers mainly in spring, was sympatric with one of two autumn flowering gorse species, U. gallii and U. minor. We noticed that E. ulicis laid eggs in spring and was restricted to U. europaeus whereas E. lemovicinum laid eggs in autumn and was restricted to the two autumn‐flowering species U. gallii and U. minor. Therefore, host specificity depended on gorse phenology, and not on geographic proximity. In addition, the infested pod content showed that E. ulicis laid several eggs per pod and suggested that females chose pods with the highest numbers of seeds. In contrast, E. lemovicinum laid a single egg per pod and showed no preference for pods with many seeds. Finally, the impact of seed predation by E. ulicis was higher than that of E. lemovicinum.     

Weak interactions between avian and insect frugivores: the case of Pistacia terebinthus L. (Anacardiaceae)

Vertebrate frugivores often feed on fruits upon or within which insects also feed, yet little information exists on the potential magnitude of interactions between these consumers. The Mediterranean shrub Pistacia terebinthus, the birds that consume its fruits, and the wasps that feed upon its seeds are examined in this study. P. terebinthus produces a highly variable fraction of final-sized red fruits that never become mature (green-colored). Red fruits can be immature, parthenocarpic, aborted, or attacked by wasps, and their pulp is much less nutritious than that of mature fruits. A total of 20 bird species consumed the fruits in the study area. Legitimate dispersers accounted for 39% of the total fruit removal, while pulp eaters and seed predators accounted for the remainder. Birds strongly preferred the mature fruits (only 4% of the fruits consumed were red). The incidence of wasps in the seeds ranged from 0 to 42% of the crop in 1989 and from 0 to 24% in 1990. The influence of avian and insect frugivore guilds on each other appears to be quite low because of the narrow overlap in resource utilization by birds and wasps, and an overall low intensity of wasp seed predation. From an evolutionary perspective, the possible ability of wasps to preclude fruit maturation appears not to be attributable to the present interaction with avian frugivores.     

Multi‐spectroscopic and molecular modeling investigation of the interactions between prantschimgin and matrix metalloproteinase 9 (MMP9)

The binding of prantschimgin (PRAN) to matrix metalloproteinase 9 (MMP9) was investigated using multiple techniques. Fluorescence spectroscopy showed that PRAN could quench the MMP9 fluorescence spectra. Changes in the UV/vis and Fourier transform infrared (FTIR) spectra were observed upon ligand binding, along with a significant degree of tryptophan fluorescence quenching on complex formation. The interaction of PRAN with MMP9 has also been studied using molecular docking and molecular dynamics (MD) simulation. The binding models demonstrated aspects of PRAN's conformation, active site interaction, important amino acids and hydrogen bonding. Computational mapping of the possible binding site of PRAN revealed that the ligand is bound in a large hydrophobic cavity of MMP9. The MD simulation results suggested that this ligand can interact with the protein, with little affecting the secondary structure. The results not only lead to a better understanding of interactions between PRAN and MMP9, but also provide useful data about the influence of PRAN on the structural conformation. The data provided in this study will be useful for designing a new agonist of MMP9 with the desired activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Pollinator-mediated interactions between a pathogenic fungus, Uromyces pisi (Pucciniaceae), and its host plant,Euphorbia cyparissias (Euphorbiaceae)

The plant Euphorbia cyparissias is commonly infected by rust fungi of the species complex Uromyces pisi. When infected, E. cyparissias is unable to flower, but instead is induced by the fungus to form pseudoflowers. Pseudoflowers are rosettes of yellow leaves upon which the fungus presents its gametes in a sweet-smelling fungal nectar. We hypothesized that the fungi, as they are heterothallic, are dependent on insect visitation to cross-fertilize their mating types. We confirmed that insects are required with an insect exclusion experiment. We further hypothesized that pseudoflowers of U. pisi interact with uninfected true host flowers through insects during their period of co-"flowering" in early spring. We conducted artificial array experiments in the field to test whether the two species share insects and whether they influenced each other's insect visitation. Insects moved between true flowers and pseudoflowers, but true flowers received more visits over all. Pseudoflowers and true flowers did not influence each other's visitation rates in mixtures. However, shorter visits were observed on pseudoflowers in mixtures than monocultures, suggesting that true flowers might be competitors for pseudoflowers. Further experiments are needed to determine whether the similarity of pseudoflowers to true flowers is adaptive.