Interaction between beech and spruce trees in temperate forests affects water use, root water uptake pattern and canopy structure

Beneficial and negative effects of species interactions can strongly influence water fluxes in forest ecosystems. However, little is known about how trees dynamically adjust their water use when growing with interspecific neighbours. Therefore, we investigated the interaction effects between Fagus sylvatica (European beech) and Picea abies (Norway spruce) on water-use strategies and aboveground structural characteristics. We used continuous in situ isotope spectroscopy of xylem and soil water to investigate source water dynamics and root water uptake depths. Picea abies exhibited a reduced sun-exposed crown area in equally mixed compared with spruce-dominated sites, which was further correlated to a reduction in sap flow of -14.5 ± 8.2%. Contrarily, F. sylvatica trees showed +13.3 ± 33.3% higher water fluxes in equally mixed compared with beech-dominated forest sites. Although a significantly higher crown interference by neighbouring trees was observed, no correlation of water fluxes and crown structure was found. High time-resolved xylem δ2H values showed a large plasticity of tree water use (-74.1 to -28.5‰), reflecting the δ2H dynamics of soil and especially precipitation water sources. Fagus sylvatica in equally mixed sites shifted water uptake to deeper soil layers, while uptake of fresh precipitation was faster in beech-dominated sites. Our continuous in situ water stable isotope measurements traced root water uptake dynamics at unprecedented temporal resolution, indicating highly dynamic use of water sources in response to precipitation and to neighbouring species competition. Understanding this plasticity may be highly relevant in the context of increasing water scarcity and precipitation variability under climate change.

A Community-Based Framework Integrates Interspecific Interactions into Forest Genetic Conservation

Forest genetic conservation is typically species-specific and does not integrate interspecific interaction and community structure. It mainly focuses on the theories of population and quantitative genetics. This approach depicts the intraspecific patterns of population genetic structure derived from genetic markers and the genetic differentiation of adaptive quantitative traits in provenance trials. However, it neglects possible interspecific interaction in natural forests and overlooks natural hybridization or subspeciation. We propose that the genetic diversity of a given species in a forest community is shaped by both intraspecific population and interspecific community evolutionary processes, and expand the traditional forest genetic conservation concept under the community ecology framework. We show that a community-specific phylogeny derived from molecular markers would allow us to explore the genetic mechanisms of a tree species interacting with other resident species. It would also facilitate the exploration of a species' ecological role in forest community assembly and the taxonomic relationship of the species with other species specific to its resident forest community. Phylogenetic β-diversity would assess the similarities and differences of a tree species across communities regarding ecological function, the strength of selection pressure, and the nature and extent of its interaction with other species. Our forest genetic conservation proposal that integrates intraspecific population and interspecific community genetic variations is suitable for conserving a taxonomic species complex and maintaining its evolutionary potential in natural forests. This provides complementary information to conventional population and quantitative genetics-based conservation strategies.

Competition-cooperation mechanism between Escherichia coli and Staphylococcus aureus based on systems mapping

Introduction

Interspecies interactions are a crucial driving force of species evolution. The genes of each coexisting species play a pivotal role in shaping the structure and function within the community, but how to identify them at the genome-wide level has always been challenging.

Methods

In this study, we embed the Lotka-Volterra ordinary differential equations in the theory of community ecology into the systems mapping model, so that this model can not only describe how the quantitative trait loci (QTL) of a species directly affects its own phenotype, but also describe the QTL of the species how to indirectly affect the phenotype of its interacting species, and how QTL from different species affects community behavior through epistatic interactions.

Results

By designing and implementing a co-culture experiment for 100 pairs of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), we mapped 244 significant QTL combinations in the interaction process of the two bacteria using this model, including 69 QTLs from E. coli and 59 QTLs from S. aureus, respectively. Through gene annotation, we obtained 57 genes in E. coli, among which the genes with higher frequency were ypdC, nrfC, yphH, acrE, dcuS, rpnE, and ptsA, while we obtained 43 genes in S. aureus, among which the genes with higher frequency were ebh, SAOUHSC_00172, capF, gdpP, orfX, bsaA, and phnE1.

Discussion

By dividing the overall growth into independent growth and interactive growth, we could estimate how QTLs modulate interspecific competition and cooperation. Based on the quantitative genetic model, we can obtain the direct genetic effect, indirect genetic effect, and genome-genome epistatic effect related to interspecific interaction genes, and then further mine the hub genes in the QTL networks, which will be particularly useful for inferring and predicting the genetic mechanisms of community dynamics and evolution. Systems mapping can provide a tool for studying the mechanism of competition and cooperation among bacteria in co-culture, and this framework can lay the foundation for a more comprehensive and systematic study of species interactions.

Research progress on productivity of mixed forest

One of the effective ways to improve the productivity of mixed forests is enhancing resource use efficiency based on the biological characteristics of afforestation tree species. Resource use efficiency is affected by tree species interactions and environmental conditions through applying appropriate cultivation patterns. In this study, we evaluated two estimating methods for the productivity of mixed forest, analyzed the internal mechanism of interspecific tree competition and complementary effects on mixed forest productivity, clarified external factors of growth space and habitat factors control over productivity of mixed forest, discussed the effects of tree species composition, stand density and site quality on productivity, and illustrated the productivity trajectory during the development of mixed forests. Finally, based on the knowledge of the internal mechanism and habitat factors affecting the formation of mixed forest productivity, we focused on the key scientific issues that urgently need to be solved in the construction of the current mixed forests cultivation patterns, and put forward future research directions, including improving the productivity estimation system, establishing long-term mixed forest observation field, enhancing the research on the comprehensive effect of various cultivation measures, and reinforcing research of the growth and development dynamics in mixed forests.

Inferior plant competitor allocates more biomass to belowground as a result of greater competition for resources in heterogeneous habitats

Nutrient heterogeneity in soil widely exists in nature and can have significant impacts on plant growth, biomass allocation, and competitive interactions. However, limited research has been done to investigate the interspecific competitive intensity between two clonal species in a heterogeneous habitat. Therefore, this greenhouse experiment was conducted with two clonal species, Phragmites australis and Scirpus planiculumis, exposed to heterogeneous and homogeneous patches of soil nutrients at five different planting ratios (0:4, 1:3, 2:2, 3:1 and 4:0), to assess the effects of both soil heterogeneity and interspecific competition on plant growth. It was found that soil nutrient heterogeneity significantly enhanced P. australis' interspecific competitive capacity and biomass by promoting a 20% increase in belowground allocation. Interestingly, the planting ratio did not affect the magnitude of this net outcome. In contrast, the superior competitor S. planiculumis did not exhibit significant change of growth indicators to the heterogeneous soil patches. These findings imply that the uncertainties associated with human-induced redistribution of plant species may lead to a shift in dominance from other species to those like P. australis, which have strong nutrient foraging abilities in response to heterogeneity in emergent wetland plant communities.

The invasive Spodoptera frugiperda (J.E. Smith) has displaced Ostrinia furnacalis (Guenée) as the dominant maize pest in the border area of southwestern China

BACKGROUND

The invasive fall armyworm (FAW) Spodoptera frugiperda (Lepidoptera: Noctuidae) has widely colonized the tropics and subtropics of Asia. However, the impact on the succession of the Asiatic corn borer (ACB) Ostrinia furnacalis (Lepidoptera: Pyralidae), a perennial dominant stemborer of maize in these areas, remains elusive. Here we analyzed the predation relationship, mimicked population competition, and surveyed the pest populations in the border area of Yunnan (southwestern China).

RESULTS

Laboratory assays revealed that the 2nd to 6th instar larvae of FAW preyed on ACB, and only the 4th and 5th instar larvae of ACB preyed on FAW (1st instar larvae only, 50% predation rate). The 6th instar FAW preyed on the 1st to 5th instar ACB with a theoretical maximum of 14.5-58.8 ACB individuals (per maize leaf) and 4.8-25.6 individuals (per tassel). When maize plants were infested with eggs of either FAW or ACB in field cage trials, maize damage was 77.6% and 50.6%, respectively, compared with 77.9% and 2.8% upon co-infestation. In field surveys conducted in 2019-2021, FAW density was significantly greater than that of ACB, which took a great impact on maize growth.

CONCLUSION

Our findings indicate that FAW can outcompete ACB at both the individual and population levels, which may result in FAW becoming the dominant pest. These results provide a scientific basis for further analysis of the mechanism by which FAW invades new agricultural areas and offers early-warning strategies for pest management. © 2023 Society of Chemical Industry.

L-phenylalanine in potato onion (Allium cepa var. aggregatum G. Don) root exudates mediates neighbor detection and trigger physio-morphological root responses of tomato

INTERACTION

Despite numerous recent insights into neighbor detection and belowground plant communication mediated by root exudates, less is known about the specificity and nature of substances within root exudates and the mechanism by which they may act belowground in root-root interactions.

METHODS

Here, we used a coculture experiment to study the root length density (RLD) of tomato (Solanum lycopersicum L.) grown with potato onion (Allium cepa var. aggregatum G. Don) cultivars with growth-promoting (S-potato onion) or no growth-promoting (N-potato onion) effects.

RESULTS AND DISCUSSION

Tomato plants grown with growth-promoting potato onion or its root exudates increased root distribution and length density oppositely and grew their roots away as compared to when grown with potato onion of no growth-promoting potential, its root exudates, and control (tomato monoculture/distilled water treatment). Root exudates profiling of two potato onion cultivars by UPLC-Q-TOF/MS showed that L-phenylalanine was only found in root exudates of S-potato onion. The role of L-phenylalanine was further confirmed in a box experiment in which it altered tomato root distribution and forced the roots grow away. In vitro trial revealed that tomato seedlings root exposed to L-phenylalanine changed the auxin distribution, decreased the concentration of amyloplasts in columella cells of roots, and changed the root deviation angle to grow away from the addition side. These results suggest that L-phenylalanine in S-potato onion root exudates may act as an "active compound" and trigger physio-morphological changes in neighboring tomato roots.

Strongly exclusive distribution with putative character displacement in two flying stag beetles

Character displacement is considered a key driver of evolutionary divergence and adaptation. Few examples of reproductive character displacement with a narrow contact zone have been identified. We examined the genetic structure, body length variation, and genital morphology in the contact and allopatric areas of Platycerus takakuwai and P. viridicuprus to investigate character displacement and gene flow. In the contact area, the species identifications based on endophallic morphology and nuclear genes were identical, whereas mitochondrial gene did not exhibit a perfect match. This incongruence suggests that interspecific hybridization followed by the mitochondrial introgression has likely occurred during historical secondary contact. The species are essentially parapatric in contact area, co-occurring at only one of 28 adjacent sampling sites despite being flying species, and no hybrids based on morphology have been found, which indicates a strongly exclusive distribution. The results showed that the body length variation was consistent with character displacement after controlling for variation along geographic and environmental gradients. Interspecific body size differentiation may have evolved to reduce incorrect mating between the species. Moreover, selective pressure caused by reproductive interference between the two species may act on body size that have likely resulted in strongly exclusive distribution at the edge of their ranges.

Direct and Indirect Competitive Interactions between Ooencyrtus nezarae and Paratelenomus saccharalis Parasitizing Megacopta cribraria Egg Patches

The present study investigated egg parasitoid interspecific interactions between a generalist, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and a specialist, Paratelenomus saccharalis Dodd (Hymenoptera: Platygastridae) in a laboratory setting using kudzu bug (Megacopta cribraria Fabricius, (Hemiptera: Plataspidae)) eggs as their shared host. Three experiments were conducted to evaluate the emergence of wasps from parasitized hosts after the simultaneous and sequential release of wasps, monitor aggressive behavior of P. saccharalis, and quantify intraguild predation of O. nezarae larvae on heterospecific P. saccharalis larvae. Results showed that total host egg parasitism was higher when both wasps were released simultaneously than if wasps were released sequentially. Ooencyrtus nezarae produced more total offspring than P. saccharalis in all sequential/simultaneous treatments but produced male offspring in most cases. In the aggressive behavioral experiment, specialist, P. saccharalis used head butting to fight O. nezarae, but no other aggressions were observed. In an experiment examining intraguild predation, O. nezarae was able to develop in host eggs parasitized by P. saccharalis four days earlier, acting as a superior larval competitor. These findings shed light on the potential interspecific interactions between O. nezarae and P. saccharalis, which may determine their relative abundance and influence their compatibility in kudzu bug biological control programs.

Co-occurrence models fail to infer underlying patterns of avoidance and aggregation when closure is violated

Advances in multi‐species monitoring have prompted an increase in the use of multi‐species occupancy analyses to assess patterns of co‐occurrence among species, even when data were collected at scales likely violating the assumption that sites were closed to changes in the occupancy state for the target species. Violating the closure assumption may lead to erroneous conclusions related to patterns of co‐occurrence among species. Occurrence for two hypothetical species was simulated under patterns of avoidance, aggregation, or independence, when the closure assumption was either met or not. Simulated populations were sampled at two levels (N = 250 or 100 sites) and two scales of temporal resolution for surveys. Sample data were analyzed with conditional two‐species occupancy models, and performance was assessed based on the proportion of simulations recovering the true pattern of co‐occurrence. Estimates of occupancy were unbiased when closure was met, but biased when closure violations occurred; bias increased when sample size was small and encounter histories were collapsed to a large‐scale temporal resolution. When closure was met and patterns of avoidance and aggregation were simulated, conditional two‐species models tended to correctly find support for non‐independence, and estimated species interaction factors (SIF) aligned with predicted values. By contrast, when closure was violated, models tended to incorrectly infer a pattern of independence and power to detect simulated patterns of avoidance or aggregation that decreased with smaller sample size. Results suggest that when the closure assumption is violated, co‐occurrence models often fail to detect underlying patterns of avoidance or aggregation, and incorrectly identify a pattern of independence among species, which could have negative consequences for our understanding of species interactions and conservation efforts. Thus, when closure is violated, inferred patterns of independence from multi‐species occupancy should be interpreted cautiously, and evidence of avoidance or aggregation is likely a conservative estimate of true pattern or interaction.

Contrasting effects of human settlement on the interaction among sympatric apex carnivores

In the face of a growing human footprint, understanding interactions among threatened large carnivores is fundamental to effectively mitigating anthropogenic threats and managing species. Using data from a large-scale camera trap survey, we investigated the effects of environmental and anthropogenic variables on the interspecific interaction of a carnivore guild comprising of tiger, leopard and dhole in Bhutan. We demonstrate the complex effects of human settlement density on large carnivore interactions. Specifically, we demonstrate that leopard–dhole co-occupancy probability was higher in areas with higher human settlement density. The opposite was true for tiger–leopard co-occupancy probability, but it was positively affected by large prey (gaur) abundance. These findings suggest that multi-carnivore communities across land-use gradients are spatially structured and mediated also by human presence and/or the availability of natural prey. Our findings show that space-use patterns are driven by a combination of the behavioural mechanism of each species and its interactions with competing species. The duality of the effect of settlement density on species interactions suggests that the benefits of exploiting anthropogenic environments are a trade-off between ecological opportunity (food subsidies or easy prey) and the risk of escalating conflict with humans.

A Holling Functional Response Model for Mapping QTLs Governing Interspecific Interactions

Genes play an important role in community ecology and evolution, but how to identify the genes that affect community dynamics at the whole genome level is very challenging. Here, we develop a Holling type II functional response model for mapping quantitative trait loci (QTLs) that govern interspecific interactions. The model, integrated with generalized Lotka-Volterra differential dynamic equations, shows a better capacity to reveal the dynamic complexity of inter-species interactions than classic competition models. By applying the new model to a published mapping data from a competition experiment of two microbial species, we identify a set of previously uncharacterized QTLs that are specifically responsible for microbial cooperation and competition. The model can not only characterize how these QTLs affect microbial interactions, but also address how change in ecological interactions activates the genetic effects of the QTLs. This model provides a quantitative means of predicting the genetic architecture that shapes the dynamic behavior of ecological communities.

Adult House Fly (Diptera: Muscidae) Response to Black Soldier Fly (Diptera: Stratiomyidae) Associated Substrates and Potential Volatile Organic Compounds Identification

Black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), larvae are suspected to inhibit house flies, Musca domestica (L.) (Diptera: Muscidae), seeking oviposition sites. However, the mechanisms regulating these interactions are not well known. In this study, a Y-tube olfactometer was used to determine whether black soldier fly eggs, larvae, puparia (without pupae inside), adult carcasses, or resulting frass of black soldier fly decrease attractiveness of adult house flies to an oviposition substrate (i.e., sugar and wheat bran diet, used as the control). Secondly, two symbiotic bacteria associated were isolated, identified, and tested for house fly attractiveness with a Y-tube olfactometer. Thirdly, volatile organic compounds produced by swine feed before and after black soldier fly, or house fly larval digestion were analyzed with gas chromatography-mass spectrometry (GC-MS). Results indicate feed mixed with black soldier fly larval frass, and symbiotic bacteria, Paenalcaligenes sp. associated with black soldier fly, were less attractive to house flies than the control. However, another symbiotic bacterium Lysinibacillus sp. associated with black soldier fly pupae was attractive. In total, 52 volatile organic compounds were identified from treatments previously described. Quantitative differences in volatile profiles across treatments potentially explain the mechanism regulating house fly substrate choices in the presence, or absence, of black soldier fly larvae.

Potential displacement of the native Tenuisvalvae notata by the invasive Cryptolaemus montrouzieri in South America suggested by differences in climate suitability

Tenuisvalvae notata (Mulsant) (Coccinellidae) is a predatory ladybird beetle native to South America. It specializes in mealybugs prey (Pseudococcidae), but relatively little is known about its ecology. In contrast, the ladybird beetle Cryptolaemus montrouzieri Mulsant (Coccinellidae) is indigenous to Australia and has been introduced to many countries worldwide including Brazil for biological control of mealybugs. The potential impacts of these introductions to native coccinellids have rarely been considered. The software CLIMEX estimated the climate suitability for both species as reflected in the Ecoclimatic Index (EI). Much of South America, Africa, and Australia can be considered climatically suitable for both species, but in most cases, the climate is considerably more favorable for C. montrouzieri than T. notata, especially in South America. The CLIMEX model also suggests seasonal differences in growth conditions (e.g. rainfall and temperature) that could affect the phenology of both species. These models suggest that few locations in South America would be expected to provide T. notata climatic refugia from C. montrouzieri. Although other ecological factors will also be important, such as prey availability, this analysis suggests a strong potential for displacement of a native coccinellid throughout most of its range as a consequence of the invasion by an alien competitor.

Coculture, An Efficient Biotechnology for Mining the Biosynthesis Potential of Macrofungi via Interspecies Interactions

Macrofungi, which are also known as mushrooms, can produce various bioactive constituents and have become promising resources as lead drugs and foods rich in nutritional value. However, the production of these bioactive constituents under standard laboratory conditions is inefficiency due to the silent expression of their relevant genes. Coculture, as an important activation strategy that simulates the natural living conditions of macrofungi, can activate silent genes or clusters through interspecific interactions. Coculturing not only can trigger the biosynthesis of diverse secondary metabolites and enzymes of macrofungi, but is also useful for uncovering the mechanisms of fungal interspecific interactions and novel gene functions. In this paper, coculturing among macrofungi or between macrofungi and other microorganisms, the triggering and upregulation of secondary metabolites and enzymes, the potential medicinal applications, and the fungal-fungal interaction mechanisms are reviewed. Finally, future challenges and perspectives in further advancing coculture systems are discussed.

Modeling of Interspecific Interaction of Yersinia pseudotuberculosis and Listeria monocytogenes in a Mixed-Species Biofilms with Microorganisms Isolated from Coastal Waters of the Sea of Japan

We studied the possibility of formation of mixed-species biofilms by Yersinia pseudotuberculosis and Listeria monocytogenes with marine saprotrophic bacteria Flavobacterium sp. and Micrococcus luteus isolated from the coastal waters of the Sea of Japan in summer. Model experiments showed that Flavobacterium sp. and Micrococcus luteus can form both single- and mixed-species biofilms with the specified pathogenic bacteria thus stimulating their growth. This can contribute to the preservation of the pathogens in the marine environment.

Spatial and temporal shift in the factors affecting the population dynamics of Calanus copepods in the North Sea

The swap in abundance between two Calanus species in the North Sea during the 1980s constitutes a quintessential example of regime shift, with important ecosystemic and economic repercussions because these copepods constitute a major component of the diet of larval and juvenile cods. It is hypothesized that this transition was driven by gradual changes in primary productivity, the North Atlantic Oscillation (NAO) and sea surface temperatures (SST), and yet how these factors contribute to the population dynamics of these two species and the overall regime shift remains unclear. Here, we combine a highly resolved and spatially structured longitudinal dataset with population dynamics theory-based models to obtain a thorough and more detailed description of populations' responses to the regime shift observed in the North Sea. Our analyses highlight that this transition exhibits a clear spatial structure and involved a decoupling between the dynamics of Calanus finmarchicus and the NAO in western regions and between Calanus helgolandicus and SST in the eastern regions of the North Sea. Consequently, the observed switch in abundance between these species reflects the interaction between species-specific attributes, a well-defined spatial structure with a marked east-west axis and a decoupling between the ecological drivers and Calanus population dynamics following the shift. Succinctly, we suspect that higher water temperatures have favored C. helgolandicus and resulted in restrictive conditions for C. finmarchicus, eventually overshadowing the effects of NAO detected in historical records. Overall, our study illustrates how population dynamics theory can be successfully employed to disentangle the complex and multifactorial nature of a regime shift in response to gradually changing environmental conditions.

Having the right neighbors: how tree species diversity modulates drought impacts on forests

Droughts are a rising concern for terrestrial ecosystems, particularly for forests where drought-induced reductions in tree growth and survival are reported. Biodiversity has long been acknowledged as an important component modulating ecosystem functions, including mitigating their vulnerability to climate-related stresses. Yet the impact of tree diversity on forest vulnerability to drought is unclear. In this review, consistent mechanisms are identified by which tree diversity could reduce vulnerability to drought and emerging evidence is revealed that tree diversity is not systematically positively related to drought resistance in forests. A path is suggested to further increase our knowledge on this subject in the face of climate change, proposing standardization of methods to quantitatively establish diversity impacts on the drought resistance of forests.

[Research progress in effects of interspecific interaction on medicinal plants in intercropping system]

Intercropping farming system is one of the essence of traditional agriculture in China and one of the most common and basic patterns of modern ecological planting. Intercropping system uses the principle of species diversity to create reasonable interspecific interaction conditions with obvious productivity advantages. In this paper, the interspecies interaction is divided into aboveground and underground parts from the space view, and its influence and mechanism on the yield and secondary metabolites of medicinal plants are elaborated.The interspecific interaction in the aboveground part mainly introduces the distribution and utilization of space resources among plants. The interspecific interaction in the underground part mainly introduces the soil rhizosphere effect and related mediating factors, root exudates, soil microorganisms, root space structure and soil environmental factors. On the basis of understanding the mechanism of interspecific interaction, this paper further discusses the application of intercropping in traditional Chinese medicine ecological agriculture, taking the effective control of diseases and insect pests, the increase of medicinal material yield and the improvement of medicinal material quality as the benefit index, so as to seek better advantages of intercropping and provide ideas for the utilization of intercropping production mode in traditional Chinese medicine ecological agriculture.

Effects of elevated CO2 and temperature on survival and wing dimorphism of two species of rice planthoppers (Hemiptera: Delphacidae) under interaction

BACKGROUND

Anthropogenic climate change (ACC) may have significant impacts on insect herbivore communities including pests. Two of the most important climate-change related factors are increased atmospheric concentrations of carbon dioxide (CO₂ ), and increasing mean global temperature. Although increasing attention is being paid to the biological and ecological effects of ACC, important processes such as interspecific interaction between insect herbivores have been little explored. Here, in a field experiment using the FACE (free-air CO₂ enrichment) system, we investigated the effect of elevated CO₂ and temperature on survival and wing dimorphism of two species of rice planthoppers, Laodelphax striatellus and Nilaparvata lugens under interaction.

RESULTS

The two species were grouped into five treatments of relative density (0/50, 13/37, 25/25, and 37/13, 50/0), each of which was allocated to one of a factorial combination of two CO₂ concentrations and two temperature treatments (elevated and ambient levels). Our results revealed that climatic treatment has no effects on survivorship of interspecific competing planthoppers. However, climatic treatment affected wing-form of planthoppers under interspecific interaction. For females of N. lugens, in the 37/13 ratio, proportion macropterours form was lower under elevated CO₂  + temperature than under the ambient environment or than under elevated temperature. For females of L. striatellus, proportion macropterous form did not differ among climatic treatments at each ratio treatment.

CONCLUSION

These findings illustrate that climate change-related factors, by affecting the macropetry of interspecific competing planthoppers, may influence planthopper fitness. We provide new information that could assist with forecasting outbreaks of these migratory pests. © 2020 Society of Chemical Industry.

Invasive Chromolaena odorata species specifically affects growth of its co-occurring weeds

Plant-plant interaction is essential to weed invasion success and is related to impacts on the environment. To understand interactions of the well-known invasive plant siamweed (Chromolaena odorata) and its neighbors (exotic Praxelis clematidea and native cadillo) in South China, and their competitive mechanisms above- and belowground, a multicultivation experiment was conducted. Competitive indices, plant morphological traits, soil nutrient contents, enzyme activities, and microbial biomass were measured. Competitive balance index and morphological traits revealed balanced competition between P. clematidea and siamweed, and suppressive effect of siamweed on cadillo. In coculture of siamweed and P. clematidea, the branch length of siamweed slightly lengthened, while the branch number of P. clematidea increased compared with their respective monocultures accordingly. Overall impacts of the two invaders on soil properties were near averages of their single impacts. In coculture of siamweed and cadillo, siamweed was more competitive in both light and nutrient capture; soil urease activity and acid phosphatase activity were magnified and mitigated compared with the averages of those in their respective monocultures, respectively. The species-specific results of siamweed competing with its co-occurring weeds would contribute to a better understanding of mechanism in synergistic effect of siamweed with the other invasive plants.

Cry2A rice did not affect the interspecific interactions between two rice planthoppers, Nilaparvata lugens, and Sogatella furcifera

Interspecific interactions are complex in agro-ecosystems and could be affected by agricultural technologies including transgenic crop planting. Few studies focused on the effects of Bt crops on the interspecific interactions of non-target organisms. Here we assessed the effects of transgenic cry2A rice (Cry2A rice) on the interspecific interaction between two rice planthoppers, namely, Nilaparvata lugens (the brown planthopper, BPH) and Sogatella furcifera (the white-backed planthopper, WBPH). Cry2A rice showed no significant effects on most biological parameters of these two rice planthoppers, except for wet weight of BPH female adults and development duration of WBPH female nymphs. In contrast, interspecific interactions between BPH and WBPH showed significant impacts on their biological parameters, no matter on Cry2A rice or non-transgenic control. In two-factor analysis combing rice line and interspecific interaction together, the interaction between these two factors did not affect most biological parameters of neither planthopper species, except for development duration of BPH female nymphs and WBPH nymphs (both male and female). Additionally, the egg distributions of BPH and WBPH had no significant differences between Cry2A and non-Cry2A treatments. Results of field experiments showed that Cry2A rice did not affect their population densities at most sampling dates in a five-year survey, and the interaction between BPH and WBPH showed no significant differences in both Cry2A and non-Cry2A rice paddies. In conclusion, our tested Cry2A rice would not affect the interspecific interactions between BPH and WBPH based both laboratory and field results.

Wood Decay Characteristics and Interspecific Interactions Control Bacterial Community Succession in Populus grandidentata (Bigtooth Aspen)

Few studies have investigated bacterial community succession and the role of bacterial decomposition over a continuum of wood decay. Here, we identified how (i) the diversity and abundance of bacteria changed along a chronosequence of decay in Populus grandidentata (bigtooth aspen); (ii) bacterial community succession was dependent on the physical and chemical characteristics of the wood; (iii) interspecific bacterial interactions may mediate community structure. Four hundred and fifty-nine taxa were identified through Illumina sequencing of 16S rRNA amplicons from samples taken along a continuum of decay, representing standing dead trees, downed wood, and soil. Community diversity increased as decomposition progressed, peaking in the most decomposed trees. While a small proportion of taxa displayed a significant pattern in regards to decay status of the host log, many bacterial taxa followed a stochastic distribution. Changes in the water availability and chemical composition of standing dead and downed trees and soil were strongly coupled with shifts in bacterial communities. Nitrogen was a major driver of succession and nitrogen-fixing taxa of the order Rhizobiales were abundant early in decomposition. Recently downed logs shared 65% of their bacterial abundance with the microbiomes of standing dead trees while only sharing 16% with soil. As decay proceeds, bacterial communities appear to respond less to shifting resource availability and more to interspecific bacterial interactions – we report an increase in both the proportion (+9.3%) and the intensity (+62.3%) of interspecific interactions in later stages of decomposition, suggesting the emergence of a more complex community structure as wood decay progresses.

Coexistence of Microbial Species in Structured Communities by Forming a Hawk-Dove Game Like Interactive Relationship

Microorganisms evolve kinds of elaborate interaction models that can form relatively stable communities in a wide range of ecosystems. It is recognized that the spatial genetic structure of microbes in surface-attached environments lays a good foundation for the persistence of polymicrobial communities in adverse conditions. However, the interacting dynamics of microbes in facilitating the formation and stabilization of community structure still remains elusive. In this study, we identify a hawk-dove game like interspecific relationship between the two Gram-negative opportunistic pathogens Pseudomonas aeruginosa and Klebsiella pneumoniae, which naturally coexist in insect gut and can cocolonize human tissues. Specifically, although P. aeruginosa had significant competitive advantage over cocultured K. pneumoniae on solid medium with rich nutrient factors, K. pneumoniae could resist the suppression of P. aeruginosa by enhancing the expression of membrane transporters induced by the extracellular metabolites of P. aeruginosa. By contrast, under the condition that K. pneumoniae had a growth advantage but P. aeruginosa met a metabolic burden in producing quorum-sensing-controlled extracellular products, the frequency of K. pneumoniae would be slightly higher than P. aeruginosa during the coexistence because K. pneumoniae was also capable of exploiting the extracellular metabolite from P. aeruginosa. In addition, P. aeruginosa quorum-sensing variant could reap benefits from K. pneumoniae in turn and reach a relatively stable two species equilibrium. These findings provide an explanation for the formation and maintenance of polymicrobial communities in different spatially structured environments, and thus may contribute to understanding the complex interspecific interactions of microbes in local communities and shed new light on the development of social microbiology.

Friendship across species borders: factors that facilitate and constrain heterospecific sociality

Our understanding of animal sociality is based almost entirely on single-species sociality. Heterospecific sociality, although documented in numerous taxa and contexts, remains at the margins of sociality research and is rarely investigated in conjunction with single-species sociality. This could be because heterospecific and single-species sociality are thought to be based on fundamentally different mechanisms. However, our literature survey shows that heterospecific sociality based on mechanisms similar to single-species sociality is reported from many taxa, contexts and for various benefits. Therefore, we propose a conceptual framework to understand conspecific versus heterospecific social partner choice. Previous attempts, which are all in the context of social information, model partner choice as a trade-off between information benefit and competition cost, along a single phenotypic distance axis. Our framework of partner choice considers both direct grouping benefits and information benefits, allows heterospecific and conspecific partners to differ in degree and qualitatively, and uses a multi-dimensional trait space analysis of costs (competition and activity matching) and benefits (relevance of partner and quality of partner). We conclude that social partner choice is best-viewed as a continuum: some social benefits are obtainable only from conspecifics, some only from dissimilar heterospecifics, while many are potentially obtainable from conspecifics and heterospecifics.This article is part of the theme issue 'Collective movement ecology'.

An ecophysiological perspective on likely giant panda habitat responses to climate change

Threatened and endangered species are more vulnerable to climate change due to small population and specific geographical distribution. Therefore, identifying and incorporating the biological processes underlying a species' adaptation to its environment are important for determining whether they can persist in situ. Correlative models are widely used to predict species' distribution changes, but generally fail to capture the buffering capacity of organisms. Giant pandas (Ailuropoda melanoleuca) live in topographically complex mountains and are known to avoid heat stress. Although many studies have found that climate change will lead to severe habitat loss and threaten previous conservation efforts, the mechanisms underlying panda's responses to climate change have not been explored. Here, we present a case study in Daxiangling Mountains, one of the six Mountain Systems that giant panda distributes. We used a mechanistic model, Niche Mapper, to explore what are likely panda habitat response to climate change taking physiological, behavioral and ecological responses into account, through which we map panda's climatic suitable activity area (SAA) for the first time. We combined SAA with bamboo forest distribution to yield highly suitable habitat (HSH) and seasonal suitable habitat (SSH), and their temporal dynamics under climate change were predicted. In general, SAA in the hottest month (July) would reduce 11.7%-52.2% by 2070, which is more moderate than predicted bamboo habitat loss (45.6%-86.9%). Limited by the availability of bamboo and forest, panda's suitable habitat loss increases, and only 15.5%-68.8% of current HSH would remain in 2070. Our method of mechanistic modeling can help to distinguish whether habitat loss is caused by thermal environmental deterioration or food loss under climate change. Furthermore, mechanistic models can produce robust predictions by incorporating ecophysiological feedbacks and minimizing extrapolation into novel environments. We suggest that a mechanistic approach should be incorporated into distribution predictions and conservation planning.

The Cyanobacterium Cylindrospermopsis raciborskii (CYRF-01) Responds to Environmental Stresses with Increased Vesiculation Detected at Single-Cell Resolution

Secretion of membrane-limited vesicles, collectively termed extracellular vesicles (EVs), is an important biological process of both eukaryotic and prokaryotic cells. This process has been observed in bacteria, but remains to be better characterized at high resolution in cyanobacteria. In the present work, we address the release of EVs by Cylindrospermopsis raciborskii (CYRF-01), a filamentous bloom-forming cyanobacterium, exposed to environmental stressors. First, non-axenic cultures of C. raciborskii (CYRF-01) were exposed to ultraviolet radiation (UVA + UVB) over a 6 h period, which is known to induce structural damage to this species. Second, C. raciborskii was co-cultured in interaction with another cyanobacterium species, Microcystis aeruginosa (MIRF-01), over a 24 h period. After the incubation times, cell density and viability were analyzed, and samples were processed for transmission electron microscopy (TEM). Our ultrastructural analyses revealed that C. raciborskii constitutively releases EVs from the outer membrane during its normal growth and amplifies such ability in response to environmental stressors. Both situations induced significant formation of outer membrane vesicles (OMVs) by C. raciborskii compared to control cells. Quantitative TEM revealed an increase of 48% (UV) and 60% (interaction) in the OMV numbers compared to control groups. Considering all groups, the OMVs ranged in size from 20 to 300 nm in diameter, with most OMVs showing diameters between 20 and 140 nm. Additionally, we detected that OMV formation is accompanied by phosphatidylserine exposure, a molecular event also observed in EV-secreting eukaryotic cells. Altogether, we identified for the first time that C. raciborskii has the competence to secrete OMVs and that under different stress situations the genesis of these vesicles is increased. The amplified ability of cyanobacteria to release OMVs may be associated with adaptive responses to changes in environmental conditions and interspecies cell communication.

Seeds integrate biological information about conspecific and allospecific neighbours

Numerous organisms integrate information from multiple sources and express adaptive behaviours, but how they do so at different developmental stages remains to be identified. Seeds, which are the embryonic stage of plants, need to make decisions about the timing of emergence in response to environmental cues related to survival. We investigated the timing of emergence of Plantago asiatica (Plantaginaceae) seed while manipulating the presence of Trifolium repens seed and the relatedness of neighbouring P. asiatica seed. The relatedness of neighbouring P. asiatica seed and the presence of seeds of T. repens did not on their own influence the timing of P. asiatica emergence. However, when encountering a T. repens seed, a P. asiatica seed emerged faster in the presence of a sibling seed than in the presence of a non-sibling seed. Water extracts of seeds gave the same result. We show that P. asiatica seeds integrate information about the relatedness of neighbouring P. asiatica seeds and the presence of seeds of a different species via water-soluble chemicals and adjust their emergence behaviour in response. These findings suggest the presence of kin-dependent interspecific interactions.

Interspecific interactions in solitary Aculeata - is the presence of heterospecifics important for females establishing nests?

There are several possible causes of aggregated nesting in solitary Aculeata, one being joint defense against parasites. We tested whether females prefer nesting in aggregations, even if they consist of heterospecifics. We compared the colonization and nesting parasitism of trap-nests with and without a red mason bee aggregation. The results did not support our hypothesis that females prefer nesting in aggregations. The numbers of wild Aculeata nests did not differ between trap-nests with and without an aggregation. Unexpectedly, parasitism rates were higher in trap-nests with aggregations. When analyzing only nests of wild insects (mostly wasps), the differences in parasitism disappeared. Natural nesting sites may be such a limited resource that females nested in the first trap-nest they encountered and did not discriminate between our treatments, or wasps might share too few parasites species with bees to benefit from joint nest defense.

Hydrological Conditions Affect the Interspecific Interaction between Two Emergent Wetland Species

Hydrological conditions determine the distribution of plant species in wetlands, where conditions such as water depth and hydrological fluctuations are expected to affect the interspecific interactions among emergent wetland species. To test such effects, we conducted a greenhouse experiment with three treatment categories, interspecific interaction (mixed culture or monoculture), water depth (10 or 30 cm depth), and hydrological fluctuation (static or fluctuating water level), and two common emergent wetland plant species, Scirpus planiculumis Fr. (Cyperaceae) and Phragmites australis var. baiyangdiansis (Gramineae). An increase in the water depth significantly restrained the growth of both S. planiculumis and P. australis, while hydrological fluctuations did not obviously alter the growth of either species. In addition, both water depth and hydrological fluctuations significantly affected the interspecific interaction between these two wetland species. P. australis benefited from interspecific interaction under increasing water depth and hydrological fluctuations, and the RII values were clearly positive for plants grown at a water depth that fluctuated around 30 cm. The results may have some implications for understanding how S. planiculumis and P. australis, as well as wetland communities, respond to the natural variation or human modification of hydrological conditions.

Different Non-Saccharomyces Yeast Species Stimulate Nutrient Consumption in S. cerevisiae Mixed Cultures

The growing interest of the winemaking industry on the use of non-Saccharomyces starters has prompted several studies about the physiological features of this diverse group of microorganisms. The fact that the proposed use of these new starters will almost invariably involve either simultaneous or sequential inoculation with Saccharomyces cerevisiae has also driven the attention to the potential biological interactions between different starters during wine fermentation. Our current understanding is that alternative yeast starters will affect wine features by both direct and indirect mechanisms (through metabolic or other types of interactions with S. cerevisiae). There are still few studies addressing the question of yeast-yeast interactions in winemaking by a transcriptomic approach. In a previous report, we revealed early responses of S. cerevisiae and Torulaspora delbrueckii to the presence of each other under anaerobic conditions, mainly the overexpression of genes related with sugar consumption and cell proliferation. We have now studied the response, under aerobic conditions, of S. cerevisiae to other two non-Saccharomyces species, Hanseniaspora uvarum and Candida sake, keeping T. delbrueckii as a reference; and always focusing on the early stages of the interaction. Results point to some common features of the way S. cerevisiae modifies its transcriptome in front of other yeast species, namely activation of glucose and nitrogen metabolism, being the later specific for aerobic conditions.

Survival of a specialist natural enemy experiencing resource competition with an omnivorous predator when sharing the invasive prey Tuta absoluta

Can specialist natural enemies persist in ecosystems when competing with omnivorous natural enemies for their shared prey? The consequences of omnivory have been studied theoretically, but empirical studies are still lacking. Omnivory is nevertheless common in nature and omnivorous predators coexist with specialists in many ecosystems, even when they are intraguild predators. This type of association is also common in agroecosystems in which biological control strategies are used. Our study provides an example of the outcome of such an association in the context of biological control of the invasive pest Tuta absoluta (Lepidoptera) in a tomato agroecosystem. The two natural enemies involved, that is, a specialist (Stenomesius japonicus (Hymenoptera) parasitoid) and an omnivore (Macrolophus pygmaeus (Hemiptera) predator), were able to coexist for 3 months in our experimental cages in the absence of metacommunity mechanisms (i.e., emigration and recolonization), contrary to theoretical expectations. However, they negatively affected each other's population dynamics. We found that spatial resource segregation was not a mechanism that promoted their coexistence. Regarding pest control, the specialist and omnivorous natural enemies were found to exhibit complementary functional traits, leading to the best control when together. Mechanisms that may have promoted the coexistence of the two species as well as consequences with regard to the inoculative biological control program are discussed.

Diurnal behavior and activity budget of the golden-crowned flying fox (Acerodon jubatus) in the Subic bay forest reserve area, the Philippines

Acerodon jubatus (the Golden-Crowned flying fox) is an endemic species in the Philippines, which was suspected to be a host of the Reston strain of the Ebola virus. As nocturnal animals, the flying foxes spend daytime at the roosting site, which they use for self-maintenance and reproduction. To understand the variation in diurnal behavior and time allocation for various activities in the Golden-Crowned flying fox, we investigated their daytime behavior and activity budget using instantaneous scan sampling and all occurrence focal sampling. Data collection was performed from 07:00 to 18:00 hr during January 8–17, 2017. The most frequent activity was sleeping (76.3%). The remaining activities were wing flapping (5.0%), self-grooming (4.2%), hanging relaxation (3.4%), wing spread (2.9%), movement (2.4%), mating/courtship (2.4%), aggression (1.9%), hanging alert (1.2%), excretion (0.1%) and scent marks (0.05%). The frequency of sleeping, wing flapping, self-grooming, hanging relaxation, aggression, mating/courtship and movement behaviors changed with the time of the day. Females allocated more time for resting than males, while males spent more time on the activities that helped enhance their mating opportunities, for example, movement, sexual activity and territorial behavior.

Attraction and Oviposition of Lucilia eximia (Diptera: Calliphoridae) to Resources Colonized by the Invasive Competitor Chrysomya albiceps (Diptera: Calliphoridae)

The present study aimed to determine if the presence of immatures of the invasive blow fly species Chrysomya albiceps (Wiedemann) influences the adult behavior of the native species Lucilia eximia (Wiedemann) in Brazil. The level of attraction and oviposition by the native species was assessed in a dual-choice assay. The evaluation was based on sex and stage of ovarian development of L. eximia adults to a resource not colonized (NCR) or colonized (RPC) with eggs, different instars, or densities of C. albiceps. A significant difference in attraction was observed based on sex and stages of ovarian development. Males and nongravid females were more attracted to RPC, whereas gravid females preferred NCR. Moreover, males exhibited the lowest response in all assays among the three sex categories examined. In general, adults preferably oviposited on NCR rather than RPC. Also, between the eggs and second instar treatments, L. eximia laid more eggs on RPC with eggs than second instars (predatory stage). Lucilia eximia attraction to second-instar C. albiceps at different densities was marginally significant. Overall, results indicate the invasive species, C. albiceps, is impacting the behavior of the native blow fly, L. eximia, with regards to its attraction and colonization of vertebrate carrion, which could explain why native blow fly populations have significantly decreased since the introduction of C. albiceps.

Density-dependent effects of non-native brown trout Salmo trutta on the species-area relationship in stream fish assemblages

The spatial scale and density-dependent effects of non-native brown trout Salmo trutta on species richness of fish assemblages were examined at 48 study sites in Mamachi Stream, a tributary of Chitose River, Hokkaido, Japan. The density of age ≥1 year S. trutta was high in the upstream side of the main stem of Mamachi Stream. Fish species richness increased with increasing area of study sites (habitat size), but the increasing magnitude of the species richness with area decreased with increasing age of ≥1 year S. trutta density. The relationships between age ≥1 year S. trutta, however, and presence-absence of each species seemed to be different among species. Species richness was also determined by location and physical environmental variables, i.e. it was high on the downstream side and in structurally complex environments.

Deciphering a survival strategy during the interspecific competition between Bacillus cereus MSM-S1 and Pseudomonas sp. MSM-M1

Interspecific competition in bacteria governs colony growth dynamics and pattern formation. Here, we demonstrate an interesting phenomenon of interspecific competition between Bacillus cereus MSM-S1 and Pseudomonas sp. MSM-M1, where secretion of an inhibitor by Pseudomonas sp. is used as a strategy for survival. Although B. cereus grows faster than Pseudomonas sp., in the presence of Pseudomonas sp. the population of B. cereus reduces significantly, whereas Pseudomonas sp. do not show any marked alteration in their population growth. Appearance of a zone of inhibition between growing colonies of two species on nutrient agar prevents the expanding front of the MSM-S1 colony from accessing and depleting nutrients in the region occupied by MSM-M1, thereby aiding the survival of the slower growing MSM-M1 colonies. To support our experimental results, we present simulations, based on a chemotactic model of colony growth dynamics. We demonstrate that the chemical(s) secreted by Pseudomonas sp. is responsible for the observed inhibition of growth and spatial pattern of the B. cereus MSM-S1 colony. Our experimental results are in excellent agreement with the numerical results and confirm that secreted inhibitors enable Pseudomonas sp. to survive and coexist in the presence of faster growing B. cereus, in a common niche.

Propagule Pressure, Habitat Conditions and Clonal Integration Influence the Establishment and Growth of an Invasive Clonal Plant, Alternanthera philoxeroides

Many notorious invasive plants are clonal, spreading mainly by vegetative propagules. Propagule pressure (the number of propagules) may affect the establishment, growth, and thus invasion success of these clonal plants, and such effects may also depend on habitat conditions. To understand how propagule pressure, habitat conditions and clonal integration affect the establishment and growth of the invasive clonal plants, an 8-week greenhouse with an invasive clonal plant, Alternanthera philoxeroides was conducted. High (five fragments) or low (one fragment) propagule pressure was established either in bare soil (open habitat) or dense native vegetation of Jussiaea repens (vegetative habitat), with the stolon connections either severed from or connected to the relatively older ramets. High propagule pressure greatly increased the establishment and growth of A. philoxeroides, especially when it grew in vegetative habitats. Surprisingly, high propagule pressure significantly reduced the growth of individual plants of A. philoxeroides in open habitats, whereas it did not affect the individual growth in vegetative habitats. A shift in the intraspecific interaction on A. philoxeroides from competition in open habitats to facilitation in vegetative habitats may be the main reason. Moreover, clonal integration significantly improved the growth of A. philoxeroides only in open habitats, especially with low propagule pressure, whereas it had no effects on the growth and competitive ability of A. philoxeroides in vegetative habitats, suggesting that clonal integration may be of most important for A. philoxeroides to explore new open space and spread. These findings suggest that propagule pressure may be crucial for the invasion success of A. philoxeroides, and such an effect also depends on habitat conditions.

Is competition needed for ecological character displacement? Does displacement decrease competition?

Interspecific competition for resources is generally considered to be the selective force driving ecological character displacement, and displacement is assumed to reduce competition. Skeptics of the prevalence of character displacement often cite lack of evidence of competition. The present article uses a simple model to examine whether competition is needed for character displacement and whether displacement reduces competition. It treats systems with competing resources, and considers cases when only one consumer evolves. It quantifies competition using several different measures. The analysis shows that selection for divergence of consumers occurs regardless of the level of between-resource competition or whether the indirect interaction between the consumers is competition (-,-), mutualism (+,+), or contramensalism (+,-). Also, divergent evolution always decreases the equilibrium population size of the evolving consumer. Whether divergence of one consumer reduces or increases the impact of a subsequent perturbation of the other consumer depends on the parameters and the method chosen for measuring competition. Divergence in mutualistic interactions may reduce beneficial effects of subsequent increases in the other consumer's population. The evolutionary response is driven by an increase in the relative abundance of the resource the consumer catches more rapidly. Such an increase can occur under several types of interaction.

Companion cropping with potato onion enhances the disease resistance of tomato against Verticillium dahliae

Intercropping could alleviate soil-borne diseases, however, few studies focused on the immunity of the host plant induced by the interspecific interactions. To test whether or not intercropping could enhance the disease resistance of host plant, we investigated the effect of companion cropping with potato onion on tomato Verticillium wilt caused by Verticillium dahliae (V. dahliae). To investigate the mechanisms, the root exudates were collected from tomato and potato onion which were grown together or separately, and were used to examine the antifungal activities against V. dahliae in vitro, respectively. Furthermore, RNA-seq was used to examine the expression pattern of genes related to disease resistance in tomato companied with potato onion compared to that in tomato grown alone, under the condition of infection with V. dahliae. The results showed that companion cropping with potato onion could alleviate the incidence and severity of tomato Verticillium wilt. The further studies revealed that the root exudates from tomato companied with potato onion significantly inhibited the mycelia growth and spore germination of V. dahliae. However, there were no significant effects on these two measurements for the root exudates from potato onion grown alone or from potato onion grown with tomato. RNA-seq data analysis showed the disease defense genes associated with pathogenesis-related proteins, biosynthesis of lignin, hormone metabolism and signal transduction were expressed much higher in the tomato companied with potato onion than those in the tomato grown alone, which indicated that these defense genes play important roles in tomato against V. dahliae infection, and meant that the disease resistance of tomato against V. dahliae was enhanced in the companion copping with potato onion. We proposed that companion cropping with potato onion could enhance the disease resistance of tomato against V. dahliae by regulating the expression of genes related to disease resistance response. This may be a potential mechanism for the management of soil-borne plant diseases in the intercropping system.

Asymmetric consequences of host plant occupation on the competition between the whiteflies Bemisia tabaci cryptic species MEAM1 and Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

BACKGROUND

The two common whitefly species, Bemisia tabaci (Gennadius) MEAM1 and Trialeurodes vaporariorum (Westwood), often co-occur on their host plants. The effect of host plant occupation by one species on later-arriving conspecific individuals or on the other competing species was examined.

RESULTS

Resource preoccupied by T. vaporariorum had mostly negative effects on the life history parameters of later-arriving conspecifics. Red-eyed nymph and immature survival of T. vaporariorum decreased when resource was preoccupied by conspecifics, irrespective of the previous occupation scenario. However, resource preoccupied by T. vaporariorum had only minor detrimental effects on the performance of later-arriving B. tabaci MEAM1. In the opposite colonisation sequence, previous occupation by B. tabaci MEAM1 had no significant effects on the life history parameters of later-arriving conspecifics, but severe detrimental effects were observed on the performance of later-arriving T. vaporariorum. Total immature survival of T. vaporariorum decreased in both weak and strong previous occupation situations by B. tabaci MEAM1.

CONCLUSION

The interspecific interactions between B. tabaci MEAM1 and T. vaporariorum were asymmetric, with B. tabaci MEAM1 being the superior competitor. This superiority could partially explain the rapid spread of B. tabaci MEAM1 in China.

Collective decision making and social interaction rules in mixed-species flocks of songbirds

Associations in mixed-species foraging groups are common in animals, yet have rarely been explored in the context of collective behaviour. Despite many investigations into the social and ecological conditions under which individuals should form groups, we still know little about the specific behavioural rules that individuals adopt in these contexts, or whether these can be generalized to heterospecifics. Here, we studied collective behaviour in flocks in a community of five species of woodland passerine birds. We adopted an automated data collection protocol, involving visits by RFID-tagged birds to feeding stations equipped with antennae, over two winters, recording 91 576 feeding events by 1904 individuals. We demonstrated highly synchronized feeding behaviour within patches, with birds moving towards areas of the patch with the largest proportion of the flock. Using a model of collective decision making, we then explored the underlying decision rule birds may be using when foraging in mixed-species flocks. The model tested whether birds used a different decision rule for conspecifics and heterospecifics, and whether the rules used by individuals of different species varied. We found that species differed in their response to the distribution of conspecifics and heterospecifics across foraging patches. However, simulating decisions using the different rules, which reproduced our data well, suggested that the outcome of using different decision rules by each species resulted in qualitatively similar overall patterns of movement. It is possible that the decision rules each species uses may be adjusted to variation in mean species abundance in order for individuals to maintain the same overall flock-level response. This is likely to be important for maintaining coordinated behaviour across species, and to result in quick and adaptive flock responses to food resources that are patchily distributed in space and time.

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We investigate the movement decisions by PIT-tagged birds in mixed-species flocks.

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Individuals had a strong tendency to move towards others when foraging in patches.

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We fit a model to infer decision-making rules used by birds in foraging flocks.

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Birds used rules adapted to the abundance of conspecifics and heterospecifics.

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A simple rule of attraction may be a flexible response to ecological conditions.

A model-based approach to detect interspecific interactions during biofilm development

A model-based approach was developed to detect interspecific interactions during biofilm development. This approach relied on the comparison of experimental data with a simple null model of biofilm growth dynamics where individual species grew independently of one another, except that they competed for space. Such a model was directly parameterized with a 4D confocal image series of biofilms and then used as a null model to detect interspecific interactions between pairs of bacterial species. This approach was tested in two bispecific competitive trials. In the first trial, the progressive exclusion of Pseudomonas fluorescens by Pseudomonas putida appeared to be due solely to the different intrinsic growth rates of the two strains. In contrast, modelling results suggested the presence of interference competition between Pseudomonas aeruginosa and P. putida in mixed biofilms. The authors' approach enables the detection of ecologically relevant interactions which constitute a prerequisite to building a comprehensive view of the dynamics and functioning of spatially structured bacterial communities.

Belowground neighbor perception in Arabidopsis thaliana studied by transcriptome analysis: roots of Hieracium pilosella cause biotic stress

Root-root interactions are much more sophisticated than previously thought, yet the mechanisms of belowground neighbor perception remain largely obscure. Genome-wide transcriptome analyses allow detailed insight into plant reactions to environmental cues. A root interaction trial was set up to explore both morphological and whole genome transcriptional responses in roots of Arabidopsis thaliana in the presence or absence of an inferior competitor, Hieracium pilosella. Neighbor perception was indicated by Arabidopsis roots predominantly growing away from the neighbor (segregation), while solitary plants placed more roots toward the middle of the pot. Total biomass remained unaffected. Database comparisons in transcriptome analysis revealed considerable similarity between Arabidopsis root reactions to neighbors and reactions to pathogens. Detailed analyses of the functional category "biotic stress" using MapMan tools found the sub-category "pathogenesis-related proteins" highly significantly induced. A comparison to a study on intraspecific competition brought forward a core of genes consistently involved in reactions to neighbor roots. We conclude that beyond resource depletion roots perceive neighboring roots or their associated microorganisms by a relatively uniform mechanism that involves the strong induction of pathogenesis-related proteins. In an ecological context the findings reveal that belowground neighbor detection may occur independently of resource depletion, allowing for a time advantage for the root to prepare for potential interactions.

Community ecology of container mosquitoes (Diptera: Culicidae) in Virginia following invasion by Aedes japonicus

The success of an invasive species in a new region depends on its interactions with ecologically similar resident species. Invasions by disease vector mosquitoes are important as they may have ecological and epidemiological consequences. Potential interactions of a recent invasive mosquito, Aedes japonicus Theobald, with resident species in Virginia were evaluated by sampling larvae from containers and trapping adults. Distinct species compositions were observed for artificial containers and rock pools, with Ae. albopictus most abundant in the former and Ae. japonicus in the latter. However, these two species were found to co-occur in 21.2% of containers sampled. Among the six mosquito species most common in containers from May through September, 2006, only interspecific associations of Ae. japonicus with Aedes albopictus (Skuse) and Aedes triseriatus (Say) were significant, and both were negative. In addition to differences in habitat preference, mean crowding estimates suggest that interspecific repulsion may contribute to the significant negative associations observed between these species. High relative abundances of late instars and pupae of Ae. japonicus seem to provide this species with a mechanism of evading competition with Ae. albopictus, facilitating their coexistence in artificial containers. Although annual fluctuations were observed, trends in adult populations over a 6-yr period provide no evidence of declines. In summary, this survey of diverse container types and all life stages provided only limited evidence for competitive displacements or reductions of resident container species by Ae. japonicus, as observed elsewhere in its invasive range.

Interactions between Heterodera avenae and Pratylenchus neglectus on Wheat

In a long-term field experiment, differential population densities of Heterodera avenae were produced by frequent cropping with resistant (cv. Panema) or susceptible (cv. Peniarth) oat. The two oat cultivars were equally good hosts of Pratylenchus neglectus in a glass house experiment with field soil. On wheat crops grown after oats in field experiments, P. neglectus population densities in roots were higher in plots where H. avenae had been controlled than in plots with moderate infestations (40 H. avenae eggs/g soil). The field observations indicated that the reduction in population densities of P. neglectus coincided with the development in roots of sedentary stages of the cyst nematode. Evidence for an indirect effect of H. avenae on P. neglectus was found in vitro in a split-root experiment. In the same field, grain yields of two wheat cultivars susceptible or resistant to H. avenae, but both susceptible to P. neglectus, was not reduced by P. neglectus. Alternation of H. avenae resistant and susceptible cultivars is a possible way of exploiting the inverse relationship between these nematodes, whilst controlling cyst nematode -populations in intensive cereal production systems.

Interaction of Meloidogyne javanica with Different Races of Meloidogyne incognita

The interspecific interactions of Meloidogyne javanica with races 1, 2, 3, and 4 of M. incognita on tomato were determined. Impacts of the interactions on fecundity and morphometrics of females were also examined. Mutually inhibitory interactions occurred between M. javanica and the races of M. incognita, but the negative interactions did not reflect in plant growth. Numbers of root galls, egg masses, mature females, total population, fecundity, and reproduction factor declined in concomitant treatments, but the morphometrics of the females remained unaltered. In general, mutual suppressive effects in all parameters were smaller for M. javanica than M. incognita, but some variations occurred among the races of M. incognita. Race 2 appeared to be more competitive than other races. The interaction between the species was not intense; therefore, the species coexist in mixed populations in agricultural fields.