Species-specific behavioral patterns correlate with differences in synaptic connections between homologous mechanosensory neurons

We characterized the behavioral responses of two leech species, Hirudo verbana and Erpobdella obscura, to mechanical skin stimulation and examined the interactions between the pressure mechanosensory neurons (P cells) that innervate the skin. To quantify behavioral responses, we stimulated both intact leeches and isolated body wall preparations from the two species. In response to mechanical stimulation, Hirudo showed local bending behavior, in which the body wall shortened only on the side of the stimulation. Erpobdella, in contrast, contracted both sides of the body in response to touch. To investigate the neuronal basis for this behavioral difference, we studied the interactions between P cells. Each midbody ganglion has four P cells; each cell innervates a different quadrant of the body wall. Consistent with local bending, activating any one P cell in Hirudo elicited polysynaptic inhibitory potentials in the other P cells. In contrast, the P cells in Erpobdella had excitatory polysynaptic connections, consistent with the segment-wide contraction observed in this species. In addition, activating individual P cells caused asymmetrical body wall contractions in Hirudo and symmetrical body wall contractions in Erpobdella. These results suggest that the different behavioral responses in Erpobdella and Hirudo are partly mediated by interactions among mechanosensory cells.     

Pathogenicity, Morphology, and Differentiation of Acanthamoeba

Acanthamoeba keratitis is sight threatening corneal infection caused by pathogenic Acanthamoeba. Previous studies have shown the genotypic differences between pathogenic and non-pathogenic species/strains of Acanthamoeba. In this study, we examined the morphological differences between pathogenic and non-pathogenic species/strains using scanning electron microscopy. Pathogenic Acanthamoeba exhibited higher number of acanthopodia (structures associated with the binding of amoeba to the target cells) as compared to non-pathogens. In addition, interactions of amoeba with the corneal epithelial cells were studied. Only pathogenic amoeba exhibited adhesion to epithelial cells. Further results indicated that phagocytosis occurs in the pathogenic amoeba by the formation of amoebastome (characteristic of amoeba phagocyte). This study showed that Acanthamoeba phagocytosis may be both an efficient means of obtaining nutrients for the amoeba and a significant factor in the pathogenesis of Acanthamoeba infections. Received: 2 April 2001 / Accepted: 12 April 2001     

Interspecific and intraspecific interactions between salt marsh plants: integrating the effects of environmental factors and density on plant performance

There has been much debate about the role of plant interactions in the structure and function of vegetation communities. Here the results of a pot experiment with controlled environments are described where three environmental variables (nutrients, sediment type and waterlogging) were manipulated factorially to identify their effects on the growth and intensity of interactions occurring between Spartina anglica and Puccinellia maritima. The two species were grown in split-plot planting treatments, representing intraspecific and interspecific addition series experiments, to determine individual and interactive effects of environmental factors and plant interactions on plant biomass.
Above-ground growth of both species involved interactions between the environmental and planting treatments, while below-ground, environmental factors affected the biomass irrespective of planting treatments. It was suggested that this difference in growth response is evidence that in our experiment plant interactions between the two species occur primarily at the above-ground level.
The intensity of plant interactions varied in a number of ways. First, interactions between Spartina and Puccinellia were distinctly asymmetrical, Puccinellia exerting a competitive effect on Spartina, with no reciprocal effect, and with a facilitative effect of Spartina on Puccinellia in low nutrient conditions. Second, the interactions varied in intensity in different environmental conditions. Interspecific competitive effects of Puccinellia on Spartina were more intense in conditions favourable to growth of Puccinellia and reduced or non-existent in environments with more abiotic stress. Third, intraspecific competition was found to be less intense for both species than interspecific interactions. Finally, the intensity of plant interactions involving both species was more intense above ground than below ground, with a disproportionate reduction in the intensity of interspecific competition below relative to above ground in treatments with less productive sediments and greater immersion. This is interpreted as reflecting a potential mechanism by which Spartina may be able to evade competitive neighbours.     

Transferrin-receptor interaction and iron uptake by reticulocytes of vertebrate animals — a comparative study

Summary Transferrin-receptor interactions and iron uptake were studied in eleven different species of vertebrate animals (3 eutherian mammals, 3 marsupials, 2 reptiles and 1 bird, amphibian and bony fish). In the initial experiments it was shown that the uptake of transferrin-bound iron by immature erythroid cells from marsupial and reptilian species occurs by receptor-mediated endocytosis as in other vertebrate animals.Reticulocytes were incubated with¹²⁵I-⁵⁹Fe-labelled transferrins from heterologous species and the results for iron and transferrin uptake compared with those obtained with the homologous protein. Cells from eutherian mammals were able to take up transferrin and iron from other eutherians and from the bob-tailed lizard but not from marsupials and other submammalian species. With marsupials and reptiles a similar specificity was observed, and the marsupial cells could also utilize chicken transferrin but not vice versa.The results were extended by performing competition experiments in which the cells were incubated with radiolabelled homologous transferrin in the presence of increasing concentrations of non-radioactive heterologous transferrins. From the ability of the heterologous proteins to inhibit uptake of the homologous protein relative association constants (K _a ¹) for the transferrin-receptor interactions could be calculated. TheseK _a ¹ values reflected the patterns observed in the first series of experiments.These studies demonstrate that, although specificity exists in transferrin-receptor interactions throughout the range of vertebrate animals, in several instances reactivity between widely divergent species is also observed. Hence, structural similarities have been maintained throughout evolution. Nevertheless, no evidence of interaction between transferrin and its receptor from the two divisions of the Mammalia, the eutherians and the marsupials, was observed.Abbreviations BSS Hanks balanced salt solution - PBS phosphate-buffered saline - RRS Rana Ringer solution     

Direct and indirect interactions for coexistence in a species-defined microcosm

Mechanisms for coexistence among micro-organisms were studied by using a species-defined microcosm, consisting of the bacterium Escherichia coli, the ciliate Tetrahymena thermophila and the alga Euglena gracilis. These organisms were chosen as representative of ecological functional groups i.e. decomposer, consumer and producer, respectively. Direct and indirect interactions among these organisms were evaluated by comparisons of their population dynamics in culture with different combinations of the three species. There was an E. coli cell density dependent predator–prey interaction between T. thermophila and E. coli which was only established when there were more than 10⁶ cells ml^–1 of E. coli. Indirect interactions were evaluated from the cultivation of each organism in media containing metabolites of the others. Metabolites from each population strongly accelerated the growth of their own populations and those of the others except for the self-toxicity effect of E. coli metabolites. These observations suggested that not only the cell–cell contact of direct interactions, but also metabolite-mediated indirect interactions supported the maintenance of the populations of each micro-organism and their coexistence. In natural ecosystems, there are many interactions and it is difficult to evaluate all those regulating community dynamics. The gnotobiotic microcosm used in this study was shown to be suitable for examining the specific, species–species microbial interactions.     

A study of chromosome association in hybrids between diploid species of Festuca

Hybrids between the two diploid species Festuca donax and F. drymeja had regular chromosome association, forming 7 bivalents at metaphase I. However, when the two species were crossed with a third species F. scariosa, the hybrids involving F. drymeja showed greater desynapsis than those with F. donax. When the F₁ hybrid F. donax × F. drymeja was crossed with F. scariosa, the trispecific progeny could be grouped into three classes according to the degree of desynapsis recorded. Abnormalities associated with the fusion of pollen mother cells, which produced highly polyploid cells, were also observed in the trispecific hybrids. Failure of chromosomal pairing and the occurrence of syncytes is attributed to genotypic interactions.     

The extent and costs of reproductive interference among four species of true bug

Reproductive interference arises when individuals of one species engage in reproductive activities with individuals of another, leading to fitness costs in one or both species. Reproductive interference (RI) therefore has two components. First, there must be mis-directed mating interactions. Second, there must be costs associated with these mis-directed interactions. Here we consider RI between four species of true bug in the family Lygaeidae, focusing in particular on the fitness consequences to Lygaeus equestris. The species we consider vary in their relationships with each other, including species in the same or different genus, and with or without natural overlap in their geographic ranges. First we show that inter-specific mating interactions, although not a certain outcome, are common enough to perhaps influence mating behaviour in these species (arising in up to 10 % of inter-specific pairings). Second, we show that reproductive interference can seriously reduce female fitness in L. equestris. Importantly, different species impose different costs of RI on L. equestris, with interactions with male Spilostethus pandurus inflicting fitness costs of similar magnitude to the costs of mating with con-specifics. On the other hand, mating interactions with male Oncopeltus fasciatus appear to have no effect on female fitness. In a follow-up experiment, when we allowed competition amongst just females of S. pandurus and L. equestris, the fitness of the latter was not reduced, arguing more strongly for the role of reproductive interference. However, in our final experiments under mass mating conditions with extended ecological interactions (including scope for competition for resources and cannibalism), the costs of RI were less apparent. Our data therefore suggest that the costs of RI will be context-specific and may act in concert with, or be swamped by, other ecological effects. We suggest that comparative studies of this sort that both mimic naturally occurring reproductive interference events, and also artificially generate new ones, will be necessary if we are to better understand the ecological and evolutionary significance of reproductive interference.     

Diet preferences based on sequence read count: The role of species interaction in tissue bias correction

High-throughput sequencing and metabarcoding techniques provide a unique opportunity to study predator–prey relationships. However, in animal dietary preference studies, how to properly correct tissue bias within the sequence read count and the role of interactions between co-occurring species in metabarcoding mixtures remain largely unknown. In this study, we propose two categories of tissue bias correction indices: sequence read count number per unit tissue (SCN) and its ratio form (SCN ratio). By constructing plant mock communities with different numbers of co-occurring species in metabarcoding mixtures and conducting feeding trails on captive sika deer (Cervus nippon), we demonstrate the features of the SCN and SCN ratio, evaluate their correction effects and assess the role of species interactions during tissue bias correction. Tissue differences between species are defined as the differential ability to generate sequence counts. Our study suggests that pure tissue differences among species without a species interaction is not an optimal correction index for many biomes with limited tissue differences among species. Species interactions in mixtures may amplify tissue differences, which is beneficial for tissue bias correction. However, caution must be taken because varied species interactions among communities may increase the risk of worse correction. Correction effects based on the SCN and SCN ratio are comparable, but the SCN is less influenced by control species than the SCN ratio. Based on our study, several suggestions are provided for future animal diet studies or other high-throughput sequencing studies containing tissue bias.     

A Comparison of Behavioral Interactions in Solitary and Presocial Zetoborinae Cockroaches (Blattaria,Blaberidae)

The social behavior of five species of Zetoborinae cockroaches is compared with respect to inter-individual interactions of nymphs in the laboratory. These species belong to the same Neotropical subfamily and were characterized as gregarious (Lanxoblatta emarginata, Parasphaeria boleiriana, Phortioeca nimbata, Schultesia lampyridiformis) and solitary (Thanatophyllum akinetum) by previous field studies. Our results show that gregarious species accept closer contacts than does the solitary one. The solitary species did not display especially short, infrequent or less diverse behavioral sequences when forced to remain aggregated, but its interactions are characterized by fewer acts promoting contact and more dominance-like acts. The solitary species symmetrically interacts with conspecifics and does not show specific dispersal-promoting behaviors. This suggests that the solitary behavior observed in the field for species of Zetoborinae mainly results from a passive spacing tendency and a lack of attraction for conspecifics. One of the gregarious species, P. boleiriana, was previously described as subsocial with nymphs remaining with the female in a wood chamber after brood birth. This species does not show a peculiar behavioral repertoire but its interactions are characterized by more dominance-like behaviors than are those of the non-subsocial gregarious species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Biogeography,macroecology and species' traits mediate competitive interactions in the order Lagomorpha

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Mycorrhizal associations of an invasive tree are enhanced by both genetic and environmental mechanisms

Biotic interactions involving exotic plants in their introduced ranges may differ from those of co‐occurring plant species and from interactions in their native ranges. When interactions are less negative, or more positive compared to native plant species, this may increase invasion success, and differences among ranges may cause changes in exotic plant traits. Here, we investigated arbuscular mycorrhizae (AM) associated with Triadica sebifera seedlings from populations in native (China) and introduced ranges (US) and with seedlings from US and China species within three co‐occurring genera (Liquidambar, Ulmus, Celtis) grown in multiple common gardens in both ranges. No general pattern of higher or lower AM colonization was found in the introduced range for China and US Celtis, Liquidambar, or Ulmus species. However, AM colonization was significantly higher for Triadica than for other genera, particularly in the introduced range, suggesting AM may improve Triadica's invasion success. Triadica AM colonization was higher in US than China gardens, decreased with increasing soil nitrogen in China, but was independent of soil nitrogen in the US. This might reflect a different effect of soil fertility on this mutualism among ranges. Introduced Triadica populations had higher AM colonization than native populations, particularly in US gardens, implying a possible advantage from greater AM association in the introduced range. This is the first field study demonstrating post‐introduction changes in mycorrhizal colonization of an invasive species. It indicates that there are ecological and evolutionary components to the effect of positive interactions on plant invasions.     

Intestinal inflammation alters mucosal carbohydrate foraging and monosaccharide incorporation into microbial glycans

Endogenous carbohydrates released from the intestinal mucus represent a constant source of nutrients to the intestinal microbiota. Mucus‐derived carbohydrates can also be used as building blocks in the biosynthesis of bacterial cell wall components, thereby influencing host mucosal immunity. To assess the uptake of endogenous carbohydrates by gut microbes in healthy mice and during intestinal inflammation, we applied azido‐monosaccharides that can be tracked on bacterial cell walls after conjugation with fluorophores. In interleukin‐10 deficient mice, changes in the gut microbiota were accompanied by decreased carbohydrate hydrolase activities and increased lumenal concentrations of host glycan‐derived monosaccharides. Tracking of the monosaccharide N‐azidoacetylglucosamine (GlcNAz) in caecum bacteria revealed a preferential incorporation of this carbohydrate by Xanthomonadaceae in healthy mice and by Bacteroidaceae in interleukin‐10 deficient mice. These GlcNAz‐positive Bacteroidaceae fractions mainly belonged to the species B. acidifaciens and B. vulgatus. Growth of Bacteroides species in the presence of specific monosaccharides changed their stimulatory activity toward CD11c⁺ dendritic cells. Expression of activation markers and cytokine production was highest after stimulation of dendritic cells with B. vulgatus. The variable incorporation of monosaccharides by related Bacteroides species underline the necessity to investigate intestinal bacteria down to the species level when addressing microbiota‐host interactions.     

The role of biotic interactions in shaping distributions and realised assemblages of species: implications for species distribution modelling

Predicting which species will occur together in the future, and where, remains one of the greatest challenges in ecology, and requires a sound understanding of how the abiotic and biotic environments interact with dispersal processes and history across scales. Biotic interactions and their dynamics influence species' relationships to climate, and this also has important implications for predicting future distributions of species. It is already well accepted that biotic interactions shape species' spatial distributions at local spatial extents, but the role of these interactions beyond local extents (e.g. 10 km² to global extents) are usually dismissed as unimportant. In this review we consolidate evidence for how biotic interactions shape species distributions beyond local extents and review methods for integrating biotic interactions into species distribution modelling tools. Drawing upon evidence from contemporary and palaeoecological studies of individual species ranges, functional groups, and species richness patterns, we show that biotic interactions have clearly left their mark on species distributions and realised assemblages of species across all spatial extents. We demonstrate this with examples from within and across trophic groups. A range of species distribution modelling tools is available to quantify species environmental relationships and predict species occurrence, such as: (i) integrating pairwise dependencies, (ii) using integrative predictors, and (iii) hybridising species distribution models (SDMs) with dynamic models. These methods have typically only been applied to interacting pairs of species at a single time, require a priori ecological knowledge about which species interact, and due to data paucity must assume that biotic interactions are constant in space and time. To better inform the future development of these models across spatial scales, we call for accelerated collection of spatially and temporally explicit species data. Ideally, these data should be sampled to reflect variation in the underlying environment across large spatial extents, and at fine spatial resolution. Simplified ecosystems where there are relatively few interacting species and sometimes a wealth of existing ecosystem monitoring data (e.g. arctic, alpine or island habitats) offer settings where the development of modelling tools that account for biotic interactions may be less difficult than elsewhere.     

Mistletoes Play Different Roles in a Modular Host–Parasite Network

Antagonistic interactions between host plants and mistletoes often form complex networks of interacting species. Adequate characterization of network organization requires a combination of qualitative and quantitative data. Therefore, we assessed the distribution of interactions between mistletoes and hosts in the Brazilian Pantanal and characterized the network structure in relation to nestedness and modularity. Interactions were highly asymmetric, with mistletoes presenting low host specificity (i.e., weak dependence) and with hosts being highly susceptible to mistletoe‐specific infections. We found a non‐nested and modular pattern of interactions, wherein each mistletoe species interacted with a particular set of host species. Psittacanthus spp. infected more species and individuals and also caused a high number of infections per individual, whereas the other mistletoes showed a more specialized pattern of infection. For this reason, Psittacanthus spp. were regarded as module hubs while the other mistletoe species showed a peripheral role. We hypothesize that this pattern is primarily the result of different seed dispersal systems. Although all mistletoe species in our study are bird dispersed, the frugivorous assemblage of Psittacanthus spp. is composed of a larger suite of birds, whereas Phoradendron are mainly dispersed by Euphonia species. The larger assemblage of bird species dispersing Psittacanthus seeds may also increase the number of hosts colonized and, consequently, its dominance in the study area. Nevertheless, other restrictions on the interactions among species, such as the differential capacity of mistletoe infections, defense strategies of hosts and habitat types, can also generate or enhance the observed pattern. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

Incorporating biotic interactions in the distribution models of African wild silk moths (Gonometa species,Lasiocampidae) using different representations of modelled host tree distributions

Biotic interactions influence species niches and may thus shape distributions. Nevertheless, species distribution modelling has traditionally relied exclusively on environmental factors to predict species distributions, while biotic interactions have only seldom been incorporated into models. This study tested the ability of incorporating biotic interactions, in the form of host plant distributions, to increase model performance for two host‐dependent lepidopterans of economic interest, namely the African silk moth species, Gonometa postica and Gonometa rufobrunnea (Lasiocampidae). Both species are dependent on a small number of host tree species for the completion of their life cycle. We thus expected the host plant distribution to be an important predictor of Gonometa distributions. Model performance of a species distribution model trained only on abiotic predictors was compared to four species distribution models that additionally incorporated biotic interactions in the form of four different representations of host plant distributions as predictors. We found that incorporating the moth–host plant interactions improved G. rufobrunnea model performance for all representations of host plant distribution, while for G. postica model performance only improved for one representation of host plant distribution. The best performing representation of host plant distribution differed for the two Gonometa species. While these results suggest that incorporating biotic interactions into species distribution models can improve model performance, there is inconsistency in which representation of the host tree distribution best improves predictions. Therefore, the ability of biotic interactions to improve species distribution models may be context‐specific, even for species which have obligatory interactions with other organisms.     

Multitrophic interactions drive body size variations in seed-feeding insects

1. The intensity of community interactions and the structure of food webs can be associated with an organism's body size. However, little is known about how interactions among species in multitrophic communities determine the body size of individuals exploiting the same resource. 2. This study evaluates the effects of resource size, fruit infestation, and parasitism on tibia length, a proxy measure of body size, of insects exploiting the same resource. The three most abundant seed-feeding species of Senegalia tenuifolia (Fabaceae: Mimosoideae) were selected, and the relationship between their tibia length and the interactions within the food web was estimated. The selected species were the beetles Merobruchus terani and Stator maculatopygus, and the braconid wasp Allorhogas vulgaris. 3. The body sizes of 531 specimens were measured and it was found that tibia length of each species responded differently to the interactions, demonstrating that functionally similar species may respond differently to multitrophic effects. The body size of Merobruchus terani, the most abundant species in the food web, was negatively affected by the presence of A. vulgaris, but there was a positive relationship with seed biomass and its own abundance in the fruits. The other two species were less abundant and more plastic in their responses, as a strong negative effect of M. terani presence on A. vulgaris body size was observed, as well as a strong negative effect of Coleoptera parasitism rate on S. maculatopygus body size. 4. It is concluded that morphological traits can provide information on how interactions affect species body size.     

Callose Synthase in Pinus sylvestris Response during Infection by Species of Heterobasidion annosum sensu lato with Varied Host Preferences

Strengthening of plant cell walls at the site of fungal entry is one of the earliest plant responses to fungal pathogens. The aim of our study was to characterize the pattern of callose synthase localization and callose deposition in roots of Pinus sylvestris after infection by species of the Heterobasidion annosum s.l. complex with different host specificity: H. annosum s.s., H. parviporum and H. abietinum. To address this, sense‐labelled probes and ribonuclease‐treated samples were used to determine in situ hybridizations of callose synthase by FISH method. Furthermore, determination of callose accumulation within P. sylvestris cells was carried out using aniline blue. The different species of H. annosum s.l. had distinct impacts on the callose synthase staining within plant tissues. Moreover, while inoculation with strains of H. abietinum resulted in callose synthase accumulation at the point of hyphae contact with the host cell, this was not observed with the other species. A significant difference in callose synthesis localization was observed after inoculation with varied species of H. annosum s.l. as a result of the specific interactions with the host.     

Sequence variation and structural conservation allows development of novel function and immune evasion in parasite surface protein families

Trypanosoma and Plasmodium species are unicellular, eukaryotic pathogens that have evolved the capacity to survive and proliferate within a human host, causing sleeping sickness and malaria, respectively. They have very different survival strategies. African trypanosomes divide in blood and extracellular spaces, whereas Plasmodium species invade and proliferate within host cells. Interaction with host macromolecules is central to establishment and maintenance of an infection by both parasites. Proteins that mediate these interactions are under selection pressure to bind host ligands without compromising immune avoidance strategies. In both parasites, the expansion of genes encoding a small number of protein folds has established large protein families. This has permitted both diversification to form novel ligand binding sites and variation in sequence that contributes to avoidance of immune recognition. In this review we consider two such parasite surface protein families, one from each species. In each case, known structures demonstrate how extensive sequence variation around a conserved molecular architecture provides an adaptable protein scaffold that the parasites can mobilise to mediate interactions with their hosts.     

Species interactions contribute to the success of a global plant invader

Biological invasions are ubiquitous ecological phenomena that often impact native ecosystems. Some introduced species have evolved traits that enhance their ability to compete and dominate in recipient communities. However, it is still unknown if introduced species can evolve traits that may enhance their species interactions to fuel invasion success. We tested whether Centaurea solstitialis (yellow starthistle) from introduced populations have greater performance than native counterparts, and whether they generate more beneficial plant-soil interactions. We used common garden and plant-soil feedback experiments with soils and seeds from native Eurasian and introduced Californian populations. We found that performance of Centaurea did not differ among source genotypes, implying that the success of this invasive species is not due to evolutionary changes. However, Centaurea grew significantly larger in soils from introduced regions than from native regions, indicating a reduction in natural enemy pressure from native populations. We conclude that species interactions, not evolution, may contribute to Centaurea’s invasion success in introduced populations.