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The strength and outcome of mutualistic interactions can be highly dependent on the combination of traits of the species involved. Distinct foraging strategies (e.g., hunting mode) of mutualistic predators may cause predator-prey interactions to vary, potentially affecting the strength of trophic cascades. We evaluate the causes of variation in the strength of spider-plant mutualisms by focusing on contrasting hunting modes of two spiders: an actively hunting lynx spider (Peucetia sp.) and a sit-and-wait crab spider (Misumenops argenteus). We manipulated spider species composition by assigning each plant to one of the following treatments: (1) no spiders; (2) sit-and-wait spiders only; (3) actively hunting spiders only; (4) actively hunting + sit-and-wait spiders. We then examined the independent and interactive effects of spider species on floral herbivory and fitness of the glandular trichome-bearing plant, Trichogoniopsis adenantha (Asteraceae). Both spider species increased plant fitness by suppressing herbivores and increasing ovary fertilization, but the overall net benefit of spiders was contingent on spider hunting mode. Sit-and-wait spiders promoted stronger positive cascading effects compared to actively hunting spiders. The combination of spider species suppressed herbivores in an additive manner; their combined impact on plant fitness, however, was lower than expected, suggesting that the inter-specific interaction between spiders is slightly antagonistic. Thus, both spider species combined weakened the strength of this spider-plant mutualism. Our findings offer a general framework for understanding the critical role of predator foraging mode in trophic cascades. [ABSTRACT FROM AUTHOR]

Abstract: Plant diversity is impacted by multiple global change drivers but also by altered biotic interactions with antagonist and mutualist organisms that can potentially affect species coexistence. With a 2‐year, outdoor mesocosm experiment in realistic mesic grassland communities, we explored the role of insect herbivory in impacting plant community dynamics under contrasting levels of water availability simulating altered rainfall regimes. We selected a grasshopper species (Calliptamus italicus L.) feeding predominantly on forbs while avoiding grasses. High water availability reduced species coexistence, boosting productivity while decreasing individual plant survival. At the community level, herbivores were not able to promote species coexistence but asymmetrically influenced grasses and forbs, reducing forb biomass under high water availability. Herbivores shaped individual plant responses to both abiotic conditions and individual‐neighbours’ interactions. Herbivores influenced focal plant survival by altering the effect of neighbouring plants, mitigating the negative effect of high neighbour biomass at low water availability and exacerbating it at high level of water availability. Synthesis. Altered rainfall has the capacity to change the relative strength of plant–plant interactions and also to determine the effects of herbivores on grassland communities. The complexity of the interactions between plants and herbivores and the observed context dependence indicate the need to incorporate multiple biotic and abiotic drivers to fully understand the mechanisms underlying plant dynamics and species coexistence in a changing world. [ABSTRACT FROM AUTHOR]

Abstract: Coexistence and diversity in plant communities depend upon outcomes of plant competition. Competition and coexistence can be mediated by abiotic soil nutrient differences as well as by soil microbial communities. The latter effects occur through various mechanisms including negative plant–soil feedbacks, when plants foster the build‐up of specialized pathogenic microbes, which ultimately reduce conspecific, but not heterospecific, densities. Microbial mutualists can have generalized associations with host plants, and by associating with multiple species might affect coexistence by conferring different levels of benefit to hosts. We examined the effects of abiotic differences and soil microbial communities, including mutualistic nitrogen‐fixing rhizobial bacteria, on coexistence processes and asked whether these interactions inform patterns of co‐occurrence in natural communities. We measured plant–soil feedbacks in the greenhouse for three native Trifolium species that either highly co‐occurred or were spatially repulsed at our field site. Using size‐fractioned soil microbial inocula prepared from field‐collected soils, we explored the effect of soil microbes on nodulation and the outcome of competition (relative interaction intensity). We also examined the effects of soil origin (home vs. away soil) on the outcome of competition between species. Soil microbes had strong positive effects on plant growth and nodulation. Microbes in general reduced the strength of plant competition relative to competition in sterilized soil and altered the relative strength of interactions with conspecific vs. congeneric neighbours, which often occurred in ways predicted to enhance coexistence. In one pair of highly co‐occurring Trifolium, competition was strong in sterilized soils, but these species facilitated one other in the presence of the full microbial community. The net effect of these microbes in general reduced competition while also increasing performance over that in sterilized soil, suggesting a role for soil microbial mutualists in host coexistence. Synthesis. Our results demonstrate that interactions between plants and diverse soil communities can alter plant–plant interactions and plant–soil feedbacks. They may increase niche differences and equalize fitness differences in ways consistent with observed co‐occurrence in the field. [ABSTRACT FROM AUTHOR]

Abstract: The quest for understanding the maintenance of species diversity has matured in recent decades under the umbrella of species coexistence theory, founded by Chesson (2000). The central conclusion of the theory is that coexistence at local scales depends on two opposing forces: average fitness differences between species, which drive the best‐adapted species to exclude others, and stabilizing mechanisms, which promote diversity via niche differentiation. Recent theoretical work has focussed on how interactions between plants and other organisms influence the equalizing and stabilizing forces. However, there is a lack of empirical information. Therefore, the next fundamental step is to assess the prevalence of these mechanisms for controlling plant coexistence across a wide range of interactions and systems. To that end, this special feature presents 10 theoretical, observational, or manipulative studies illustrating 9 different biotic interactions including mutualisms (pollinators, seed dispersers, soil microbes, and arbuscular mycorrhizal fungi) and antagonisms (leaf and seed herbivores, and leaf and root pathogens). All studies share a common question: how biotic interactions regulate plant coexistence? Comparisons across studies suggest that biotic interactions modify both stabilizing and average fitness differences. In those cases where biotic interactions promote stable coexistence between plant species, both mutualistic and antagonistic interactions act more frequently as an equalizing rather than as a stabilizing mechanisms. Besides these generalities, the studies of this special issue also present novel theoretical and empirical approaches to better understand the maintenance of species diversity over a wide variety of systems, environmental conditions, and organisms. Synthesis. The studies presented here constitutes a solid base to empirically explore how mutualistic and antagonistic interactions act upon the determinants of plant species competition, and open novel paths for future research. Collectively, these advances will serve to pave the road for a better theoretical and empirical understanding of how biotic interactions control biodiversity. [ABSTRACT FROM AUTHOR]

Abstract: Females of myrmecophilous butterflies tend to oviposit in plants visited by ant species that engage in stable associations with its larvae. In Banisteriopsis malifolia, caterpillars are attended by the same ants that feed on extrafloral nectaries. A conflict may arise when both the plant and caterpillars compete for ant attention, and ants are assumed to forage on the highest quality resource. By attending caterpillars, ants can be indirectly detrimental to plant fitness because florivorous larvae feed intensively until pupation. In this study, we specifically investigated (i) whether the occurrence of facultative myrmecophilous Synargis calyce (Riodinidae) caterpillars in B. malifolia was based on ant species (Camponotus blandus or Ectatomma tuberculatum) and abundance; (ii) the monopolization of ants by the butterfly larvae and (iii) the florivory rates incurred by the caterpillars on inflorescences. The abundance of S. calyce was six‐fold greater in plants with C. blandus, compared to E. tuberculatum treatments. Caterpillars monopolized up to 50% of C. blandus on the plants, indicating that the resources offered by S. calyce were more attractive to ants than extrafloral nectaries. Florivory by riodinids incurred losses of almost 60% of flower buds. Myrmecophilous riodinids exploited an ant–plant mutualism by attracting aggressive ants that become larvae bodyguards. Thus, this ecological interaction is potentially detrimental to B. malifolia, since the ants, which can provide protection against herbivores, shift to provide defence for one of these herbivores. [ABSTRACT FROM AUTHOR]

The fungal endophyte Phomopsis liquidambari can improve nitrification rates and alter the abundance and composition of ammonia-oxidizers in the soil rhizosphere of rice. Aerenchyma is related to oxygen transport efficiency and contributes to the enhanced rhizospheric nitrification under flooding conditions. However, whether and how P. liquidambari affects aerenchyma formation is largely unknown. We therefore conducted pot and hydroponic experiments to investigate the changes of aerenchyma area, ethylene and indole-3-acetic acid (IAA) levels in rice with or without P. liquidambari infection. Our results showed that the larger aerenchyma area in rice roots with P. liquidambari inoculation was associated with markedly up-regulated expression of genes related to aerenchyma formation. Meanwhile, P. liquidambari inoculation substantially elevated root porosity (POR) and radial oxygen loss (ROL), leading to the enhancement of oxidation-reduction potential (ORP) under pot condition. Besides, P. liquidambari significantly increased IAA and ethylene levels in rice by stimulating the expression of genes involved in auxin and ethylene biosyntheses. Furthermore, auxin that partly acting upstream of ethylene signalling played an essential role in P. liquidambari- promoted aerenchyma formation. These results verified the direct contribution of P. liquidambari in promoting aerenchyma formation via the accumulation of IAA and ethylene in rice roots, which provides a constructive suggestion for improving hypoxia tolerance through plant-endophyte interactions. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between granivorous scatterhoarding mammals and plants is a conditional mutualism: scatterhoarders consume seeds (acting as predators), but the movement of seed by scatterhoarders may contribute to dispersal (acting as mutualists). Understanding the ecological factors that shape this relationship is highly relevant in anthropogenically disturbed tropical forests where large‐bodied frugivores are extirpated. In such forests, large‐seeded trees that once depended on these frugivores for dispersal may now only have scatterhoarders as prospective dispersers. We studied Carapa oreophila (Meliaceae) in an Afromontane forest, to test the hypotheses that the proportion of seeds immediately consumed or hoarded (dispersed) would vary over a disturbance gradient. Temporal replication also afforded exploration of how habitat effects might vary with food availability. Using a Bayesian framework, we demonstrate that seeds were more likely to be hoarded in less disturbed forest, irrespective of temporal variation in food abundance. In contrast, forest disturbance only appeared to increase seed predation in temporal replicates that coincided with sustained food availability. These results highlight the potential variability in the dynamics between plants and scatterhoarders over fine temporal scales, elucidating possible ecological scenarios where scatterhoarders might act as mutualists (contributing positively to plant recruitment). Our study also fills important knowledge gaps about the importance of scatterhoarders as dispersers in tropical forests depleted of large‐bodied frugivores, particularly in Africa where scatterhoarding mutualisms have not been extensively studied. [ABSTRACT FROM AUTHOR]

Abstract: The evolutionary and ecological success of many insects is attributed to mutualistic partnerships with bacteria that confer hosts with novel traits including food digestion, nutrient supplementation, detoxification of harmful compounds and defence against natural enemies. Dysdercus fasciatus firebugs (Hemiptera: Pyrrhocoridae), commonly known as cotton stainers, possess a simple but distinctive gut bacterial community including B vitamin‐supplementing Coriobacteriaceae symbionts. In addition, their guts are often infested with the intestinal trypanosomatid parasite Leptomonas pyrrhocoris (Kinetoplastida: Trypanosomatidae). In this study, using experimental bioassays and fluorescence in situ hybridization (FISH), we report on the protective role of the D. fasciatus gut bacteria against L. pyrrhocoris. We artificially infected 2nd instars of dysbiotic and symbiotic insects with a parasite culture and measured parasite titres, developmental time and survival rates. Our results show that L. pyrrhocoris infection increases developmental time and slightly modifies the quantitative composition of the gut microbiota. More importantly, we found significantly higher parasite titres and a tendency towards lower survival rates in parasite‐infected dysbiotic insects compared to symbiotic controls, indicating that the gut bacteria successfully interfere with the establishment or proliferation of L. pyrrhocoris. The colonization of symbiotic bacteria on the peritrophic matrix along the gut wall, as revealed by FISH, likely acts as a barrier blocking parasite attachment or entry into the hemolymph. Our findings show that in addition to being nutritionally important, D. fasciatus’ gut bacteria complement the host's immune system in preventing parasite invasions and that a stable gut microbial community is integral for the host's health. [ABSTRACT FROM AUTHOR]

Honeydew production by Hemiptera is an ecologically important process that facilitates mutualisms and increases nutrient cycling. Accurate estimates of the amount of honeydew available in a system are essential for quantifying food web dynamics, energy flow, and the potential growth of sooty mould that inhibits plant growth. Despite the importance of honeydew, there is no standardized method to estimate its production when intensive laboratory testing is not feasible. We developed two new models to predict honeydew production, one based on insect body mass and taxonomic family, and one based on body mass and life stage. We tested the accuracy of both models’ predictions for a diverse range of honeydew-producing hemipteran families (Aphididae, Pseudococcidae, Coccidae, Psyllidae, Aleyrodidae, Delphacidae, Cicadellidae). The method based on body mass and family provided more accurate estimates of honeydew production, due to large variation in honeydew production among families. We apply our methodology to a case study, the recalculation of honeydew available to invasive red imported fire ant (Solenopsis invicta) in the United States. We find that the amount of honeydew may be an order of magnitude lower than that previously estimated (2.16 versus 21.6 grams of honeydew per day) and discuss possible reasons for the difference. We anticipate that being able to estimate honeydew production based on minimal biological information will have applications to agriculture, invasion biology, forestry, and carbon farming. [ABSTRACT FROM AUTHOR]

Epichloë endophytes form mutualistic symbiotic associations with aerial tissues of temperate grasses. Intercalary growth of hyphae within the leaves enables fungal growth to be synchronized with host leaf growth, leading to formation of a highly structured and tightly regulated symbiotic network. Mutations in fungal genes that disrupt cell–cell fusion and other key signalling pathways lead to an antagonistic interaction characterized by unregulated growth of endophytic hyphae and detrimental effects on host growth. Transcriptome analysis of these mutant associations provides key insights into the regulation of the symbiosis. In nature a similar switch in growth occurs when hyphae transition into the sexual cycle forming stromata that abort host inflorescences. Endophyte infection of the grass host leads to a major reprogramming of host metabolism and alters host development. Changes in endophyte cell wall structure and the repertoire of effectors secreted into the host apoplast accompany establishment of a mutualistic interaction within the leaves. [ABSTRACT FROM AUTHOR]

Bacterial volatile compounds (BVCs) are not waste or by-products of primary metabolism but rather have critical roles in the biology and ecological competence of bacteria. BVCs are exploited as a source of nutrients and information in plant–bacteria interactions. They target key points in plant physiology, activating downstream metabolic pathways by a domino effect. BVCs are an ancient signal and are involved in plant–bacteria communication, which was shaped during evolutionary history and established before the development of higher plants. This type of communication is not exclusive to mutualistic interactions, because pathogens also use volatiles to alter plant physiology. Here, fragmented information is drawn together to provide a clearer view of how BVCs affect such interactions. [ABSTRACT FROM AUTHOR]

Abstract. Kangaroo rats are reported to have a mutualistic relationship with harvester ants through facilitation of burrow establishment, creation, and persistence. The relationship can, however, become more complex. We report observations of the giant kangaroo rat (Dipodomys ingens), a state and federally listed endangered species, repeatedly kleptoparasitizing harvester ants from a nearby nest in the Carrizo Plain, California. Though the relationship between kangaroo rats and harvester ants has been studied extensively and is believed to be mutualistic, under certain conditions this relationship can follow an alternate path of parasitism. [ABSTRACT FROM AUTHOR]

1. Mutualisms may be particularly vulnerable to climate change as interacting species are likely to respond differently, which could destabilise interactions. 2. Temperate zone insects typically experience mean temperatures below their thermal optima, making them less vulnerable than tropical insects to small increases in mean temperature. However, they are likely to experience a higher frequency of extreme heat events, putting mutualism persistence in jeopardy. 3. This study investigated the potential impacts of climate change on Pleistodontes imperialis, a temperate Australian fig wasp that pollinates Port Jackson figs (Ficus rubiginosa). Wasp emergence and longevity were measured at temperatures ranging from those commonly experienced in nature (25 °C) to high values (> 40 °C) that are currently infrequent, but which are becoming more common with climate change. 4. Wasp emergence was unaffected by temperatures up to 39 °C, but it declined drastically above 39 °C. Adult longevity was unaffected by temperatures up to 30 °C, but decreased at 35 °C and above. Low humidity reduced wasp longevity across all temperatures. 5. Fitness reductions were observed at temperatures ∼5 °C above the summer daily mean maximum, suggesting that P. imperialis has a high thermal tolerance, but is vulnerable to extreme heat. Figs located in the shade may provide protected microhabitats under hot conditions. 6. Tropical pollinators may be threatened by small increases in mean temperature. In contrast, it is shown here that temperate pollinators may face a different primary threat from climate change – the increasing frequency of extreme heat events – despite their higher thermal tolerances. [ABSTRACT FROM AUTHOR]

1. Acceptance of hosts for oviposition is often hardwired in short‐lived insects, but can be dynamic at the individual level due to variation in physiological state determinants such as ageing and prior oviposition. However, the effect of the oviposition history of resources together with time taken to accept less preferred hosts in ageing insects has rarely been investigated. 2. The time taken by parasitic fig wasps to accept resources with different oviposition histories was recorded in order to investigate the effect of wasp physiological state and resource oviposition history on oviposition behaviour. These wasps, which differ in life‐history traits, oviposit at specific developmental stages of enclosed fig inflorescences called syconia. 3. Behavioural assays were performed with naive wasps and wasps aged with and without prior oviposition experience. Syconia at the same developmental stage but differing in oviposition history were offered in no‐choice assays and the time taken to first oviposition attempt was recorded. 4. One short‐lived pro‐ovigenic galler species exhibited a decline with age in time taken to accept a syconium for oviposition. The exact timing of the transition from non‐acceptance to acceptance of less preferred syconia was determined in terms of the proportion of elapsed life span at the transition; this occurred at 25% of elapsed life span. 5. Longer‐lived parasitoids did not show any decline in specificity despite being aged for 50% of their life span. Therefore, host quality, trophic position, egg load and age may individually affect oviposition decisions or have interaction effects. [ABSTRACT FROM AUTHOR]

1. When parasites exploit mutualisms involving food exchange, they can destabilise the partnership with costs to interacting partners. For instance, the ant Sericomyrmex amabilis farms fungal symbionts to produce food, but, in so doing, attracts parasitic Megalomyrmex symmetochus guest ants that infiltrate fungus‐farming ant societies and live with their hosts their entire lives. 2. The present study examined whether host foraging in parasitised colonies shifts towards nutritional requirements of the parasitic guest ants as inferred from the parasite's elemental content (%C, %N, and C:N). 3. Laboratory feeding experiments with nutritionally defined diets indicated that S. amabilis ants harvest protein‐biased substrate, and more total substrate when hosting M. symmetochus relative to when provisioning their fungus gardens and nestmates. 4. Field surveys further showed that parasitised colonies incur reductions in fungus garden nutritional quality and quantity, brood mass, and host worker body condition. And yet these costs appear manageable across growing seasons, as parasitised fungal cultivars appear to provide sufficient nutrition for stable populations of host ants. 5. The approach developed here shows how behavioural strategies for nutrient regulation can extend beyond the needs of the individual to entire fungus‐farming systems, and implies that S. amabilis dynamically adjusts collective foraging strategies when parasitised to enhance long‐term symbiotic stability. [ABSTRACT FROM AUTHOR]

In the animal kingdom, nutritional mutualism is a perpetual and intimate dialogue carried out between the host and its associated gut community members. This dialogue affects many aspects of the host’s development and physiology. Some constituents of the animal gut microbiota can stably reside within the host for years, and such long-term persistence might be a prerequisite for these microbes to assert their beneficial impact. How long-term persistence is established and maintained is an interesting question, and several classic model organisms associated with cultivable resident strains are used to address this question. However, in Drosophila, this model has long eluded fly geneticists. In this issue of PLOS Biology, Pais and colleagues present the most rigorous and comprehensive demonstration to date that persistence and gut residency do take place in the digestive tract of Drosophila melanogaster. This natural gut isolate of Acetobacter thailandicus stably colonizes the adult fly foregut, accelerates larval maturation, and boosts host fecundity and fertility as efficiently as the known laboratory strains. The discovery of such stable association will be a boon for the Drosophila community interested in host–microbiota interaction, as it not only provides a novel model to unravel the molecular underpinnings of persistence but also opens a new arena for using Drosophila to study the implications of gut persistence in evolution and ecology. [ABSTRACT FROM AUTHOR]

Endophytes are microorganisms that colonize the interior of host plants without causing apparent disease. They have been widely studied for their ability to modulate relationships between plants and biotic/abiotic stresses, often producing valuable secondary metabolites that can affect host physiology. Owing to the advantages of microbial fermentation over plant/cell cultivation and chemical synthesis, endophytic fungi have received significant attention as a mean for secondary metabolite production. This article summarizes currently reported results on plant-endophyte interaction hypotheses and highlights the biotechnological applications of endophytic fungi and their metabolites in agriculture, environment, biomedicine, energy, and biocatalysts. Current bottlenecks in industrial development and commercial applications as well as possible solutions are also discussed. [ABSTRACT FROM AUTHOR]

Mutualisms contribute in fundamental ways to the origin, maintenance and organization of biological diversity. Introduced species commonly participate in mutualisms, but how this phenomenon affects patterns of interactions among native mutualists remains incompletely understood. Here we examine how networks of interactions among aphid‐tending ants, ant‐tended aphids, and aphid‐attacking parasitoid wasps differ between 12 spatially paired riparian study sites with and without the introduced Argentine ant Linepithema humile in southern California. To resolve challenges in species identification, we used DNA barcoding to identify aphids and screen for parasitoid wasps (developing inside their aphid hosts) from 170 aphid aggregations sampled on arroyo willow Salix lasiolepis. Compared to uninvaded sites, invaded sites supported significantly fewer species of aphid‐tending ants and ant‐tended aphids. At invaded sites, for example, we found only two species of ant‐tended aphids, which were exclusively tended by L. humile, whereas at uninvaded sites we found 20 unique ant–aphid interactions involving eight species of ant‐tended aphids and nine species of aphid‐tending ants. Ant–aphid linkage density was thus significantly lower at invaded sites compared to uninvaded sites. We detected aphid parasitoids in 14% (28/198) of all aphid aggregations. Although the level of parasitism did not differ between invaded and uninvaded sites, more species of wasps were detected within uninvaded sites compared to invaded sites. These results provide a striking example of how the assimilation of introduced species into multi‐species mutualisms can reduce interaction diversity with potential consequences for species persistence. [ABSTRACT FROM AUTHOR]

Frugivores and fleshy-fruited plants commonly engage in the mutually beneficial interaction by dispersing seeds while consuming fruit pulps. Such mutualistic interactions can have profound impacts on the persistence and distributions of plant populations. Based on pair approximation, we here develop a process-based mechanistic model that captures the dynamics of the mean and local densities of plants and the density of animals. The model considers three components of frugivory: the strength of frugivore-plant mutualistic interaction, the efficiency of seed dispersers, and the germination probability of seeds. Results show that seed dispersal by animals is crucial to the extended persistence of plants by reducing the level of aggregation and thus local intraspecific competition. Importantly, frugivory can only be beneficial to the plants if the animal is an efficient seed disperser with limited risks/costs of dispersal plus adequate number of encounters. Otherwise, frugivory could become a main driver of plant extinction from seed predation by the animals. In conclusion, frugivorous seed dispersal could allow persistence of plants in habitats that otherwise require much higher levels of fecundity and dispersal rate to survive. Such extended persistence highlights the threshold phenomenon in plant conservation – extended persistence in environments that are difficult to restore once the plants have collapsed. [ABSTRACT FROM AUTHOR]

Plants in more than 100 families secrete extrafloral nectar (EFN) to establish food-for-protection mutualisms with ants. Facultative ant-plants secrete EFN as a jasmonic acid (JA)-dependent response to attract generalist ants. In contrast, obligate ant-plants like the Central American “Swollen-Thorn Acacias” are colonized by specialized ants, although an individual host can carry ant colonies from different species that differ in the degree of protection they provide. We hypothesized that hosts that associate simultaneously with various partners should produce rewards in a modular manner to preferentially reward high quality partners. To test this hypothesis, we applied JA to distinct leaves and quantified cell wall invertase activity (CWIN; a regulator of nectar secretion) and EFN secretion by these “local” (i.e., treated) and the “systemic” (i.e., non-treated) leaves of the same branch. Both CWIN activity and EFN secretion increased in local and systemic leaves of the facultative ant-plant Acacia cochliacantha, but only in the local leaves of the obligate ant-plant, A. cornigera. The systemic EFN secretion in A. cochliacantha was associated with an enhanced emission of volatile organic compounds (VOCs). Such VOCs function as “external signals” that control systemic defense responses in diverse plant species. Indeed, the headspace of JA-treated branches of A. cochliacantha induced EFN secretion in both plant species, whereas the headspace of A. cornigera caused no detectable induction effect. Analyses of the headspace using GC-MS identified six VOCs in the headspace of A. cochliacantha that were not emitted by A. cornigera. Among these VOCs, β-caryophyllene and (cis)-hexenyl isovalerate have already been reported in other plant species to induce defense traits, including EFN secretion. Our observations underline the importance of VOCs as systemic within-plant signals and show that the modular rewarding in A. cornigera is likely to result from a reduced emission of the systemic signal, rather than from a reduced responsiveness to the signal. We suggest that modular rewarding allows hosts to restrict the metabolic investment to specific partners and to efficiently sanction potential exploiters. [ABSTRACT FROM AUTHOR]

Microbial mutualistic cross-feeding interactions are ubiquitous and can drive important community functions. Engaging in cross-feeding undoubtedly affects the physiology and metabolism of individual species involved. However, the nature in which an individual species' physiology is influenced by cross-feeding and the importance of those physiological changes for the mutualism have received little attention. We previously developed a genetically tractable coculture to study bacterial mutualisms. The coculture consists of fermentative Escherichia coli and phototrophic Rhodopseudomonas palustris. In this coculture, E. coli anaerobically ferments sugars into excreted organic acids as a carbon source for R. palustris. In return, a genetically engineered R. palustris strain constitutively converts N2 into NH4+, providing E. coli with essential nitrogen. Using transcriptome sequencing (RNA-seq) and proteomics, we identified transcript and protein levels that differ in each partner when grown in coculture versus monoculture. When in coculture with R. palustris, E. coli gene expression changes resembled a nitrogen starvation response under the control of the transcriptional regulator NtrC. By genetically disrupting E. coli NtrC, we determined that a nitrogen starvation response is important for a stable coexistence, especially at low R. palustris NH4+ excretion levels. Destabilization of the nitrogen starvation regulatory network resulted in variable growth trends and, in some cases, extinction. Our results highlight that alternative physiological states can be important for survival within cooperative cross-feeding relationships. IMPORTANCE Mutualistic cross-feeding between microbes within multispecies communities is widespread. Studying how mutualistic interactions influence the physiology of each species involved is important for understanding how mutualisms function and persist in both natural and applied settings. Using a bacterial mutualism consisting of Rhodopseudomonas palustris and Escherichia coli growing cooperatively through bidirectional nutrient exchange, we determined that an E. coli nitrogen starvation response is important for maintaining a stable coexistence. The lack of an E. coli nitrogen starvation response ultimately destabilized the mutualism and, in some cases, led to community collapse after serial transfers. Our findings thus inform on the potential necessity of an alternative physiological state for mutualistic coexistence with another species compared to the physiology of species grown in isolation. [ABSTRACT FROM AUTHOR]

Aim: At continental scales, abiotic factors such as climate are typically used to explain differences in plant ranges. Although biotic interactions also underlie the biogeography of plants, the importance of plant-associated microbes is often overlooked when predicting ranges. In particular, symbiotic microbes may influence the distribution of plants that engage in strong interactions with them. We tested whether seedling response to inoculation by ectomycorrhizal fungi explains range size of trees. To examine mechanisms underlying the relationship between range size and response to inoculation, we also examined to what extent sympatry between host and fungi influenced this relationship. Location: Global. Time period: Contemporary. Major taxa studied: Trees and fungi forming ectomycorrhizas. Methods: Using a dataset of 1,275 observations from 126 papers, we calculated mean biomass response (effect size) of 59 tree species to fungal inoculation. We extracted host range area from digitized maps of native distributions, and determined whether hosts were naturally sympatric with fungal species used as inoculum by searching herbaria databases with geospatially referenced data. Results: Tree species with seedling effect sizes falling above or below the average response tended to have small ranges and those with average responses, large ranges. Moreover, hosts inoculated with fungi whose ranges were allopatric to their own had higher biomass compared to those that were inoculated by sympatric fungi, suggesting that the extent of geographical overlap between trees and symbiotic fungi may attenuate the mutualism. Main conclusions: We demonstrate that mycorrhizas may underlie host biogeographical patterns at the continental scale. Our study is novel in the scope of species and scale tested, and points to a possible mechanism underlying this pattern related to the process of mutualism breakdown accruing over time at local geographical scales. For ectomycorrhizal tree species, performance may increase when exposed to fungal partners without a recent shared evolutionary history. [ABSTRACT FROM AUTHOR]

Diagnosis of transient/latent HPV infections requires a rethinking of ideas concerning the host virus relationship. With this in mind, we address several concepts, such as mutualism and commensalism, to understand better the different stages of development, in addition to briefly covering current methods of detection. We suggest analyzing molecules related to the innate immune response for earlier diagnosis. [ABSTRACT FROM AUTHOR]

Summary: The gastrointestinal tract is a highly complex organ in which multiple dynamic physiological processes are tightly coordinated while interacting with a dense and extremely diverse microbial population. From establishment in early life, through to host‐microbe symbiosis in adulthood, the gut microbiota plays a vital role in our development and health. The effect of the microbiota on gut development and physiology is highlighted by anatomical and functional changes in germ‐free mice, affecting the gut epithelium, immune system and enteric nervous system. Microbial colonisation promotes competent innate and acquired mucosal immune systems, epithelial renewal, barrier integrity, and mucosal vascularisation and innervation. Interacting or shared signalling pathways across different physiological systems of the gut could explain how all these changes are coordinated during postnatal colonisation, or after the introduction of microbiota into germ‐free models. The application of cell‐based in‐vitro experimental systems and mathematical modelling can shed light on the molecular and signalling pathways which regulate the development and maintenance of homeostasis in the gut and beyond. [ABSTRACT FROM AUTHOR]

Variation in partner species and frequency of interaction between species pairs are potential drivers of the net outcome of generalized mutualisms. In ant-plant mutualisms, the quality of defence provided by ants is related to ant aggressiveness. Hence, we hypothesize that the performance of plants bearing extrafloral nectaries will be higher when they interact more frequently with more aggressive ant species. We estimated ant aggressiveness in the field by observing their behaviour towards soil baits. Afterwards, we observed the frequency with which individuals from these ant species visited plants through an entire reproductive cycle. We measured the production and persistence of plants reproductive structures through this period and the total seed production. Increasing in the interaction frequency with highly aggressive ants reduced the number of floral buds and seeds produced. Increased visitation frequency by less aggressive ants increased the number of floral buds and seeds per branch. The inverse relationship between ant aggressiveness and seed production may be influenced by the costs imposed by different mutualistic partners. Thus, frequent interaction with highly aggressive ants may lead to a higher accumulation of costs through time, resulting in a negative net outcome for the plants. Our results bring new evidence highlighting the importance to incorporate temporal aspects in the study of mutualistic interactions. We suggests that the quality of mutualistic partners must be understood as a function of its per-interaction benefit and their cumulative costs to their partner over time, what puts in check our current classification regarding partner quality in mutualistic systems. [ABSTRACT FROM AUTHOR]

Seemingly mutualistic relationships can be exploited, in some cases reducing fitness of the exploited species. In plants, the insufficient receipt of pollen limits reproduction. While infrequent pollination commonly underlies pollen limitation (PL), frequent interactions with low-efficiency, exploitative pollinators may also cause PL. In the widespread protandrous herb Campanula americana, visitation by three pollinators explained 63% of the variation in PL among populations spanning the range. Bumblebees and the mediumsized Megachile campanulae enhanced reproductive success, but small solitary bees exacerbated PL. To dissect mechanisms behind these relationships, we scored sex-specific floral visitation, and the contributions of each pollinator to plant fitness using single flower visits. Small bees and M. campanulae overvisited male-phase flowers, but bumblebees frequently visited female-phase flowers. Fewer bumblebee visits were required to saturate seed set compared to other bees. Scaling pollinator efficiency metrics to populations, small bees deplete large amounts of pollen due to highly male-biased flower visitation and infrequent pollen deposition. Thus, small bees reduce plant reproduction by limiting pollen available for transfer by efficient pollinators, and appear to exploit the plant--pollinator mutualism, acting as functional parasites to C. americana. It is therefore unlikely that small bees will compensate for reproductive failure in C. americana when bumblebees are scarce. [ABSTRACT FROM AUTHOR]

Abstract: Mutualistic interactions, where two interacting species have a net beneficial effect on each other's fitness, play a crucial role in the survival and evolution of many species. Despite substantial empirical and theoretical work in past decades, the impact of these interactions on natural selection is not fully understood. In addition, mutualisms between microorganisms have been largely ignored, even though they are ecologically important and can be used as tools to bridge the gap between theory and empirical work. Here, I describe two problems with our current understanding of natural selection in mutualism and highlight the properties of microbial mutualisms that could help solve them. One problem is that bias and methodological problems have limited our understanding of the variety of mechanisms by which species may adapt to mutualism. Another problem is that it is rare for experiments testing coevolution in mutualism to address whether each species has adapted to evolutionary changes in its partner. These problems can be addressed with genome resequencing and time‐shift experiments, techniques that are easier to perform in microorganisms. In addition, microbial mutualisms may inspire novel insights and hypotheses about natural selection in mutualism. [ABSTRACT FROM AUTHOR]

Insects harbor a community of gut bacteria, ranging from pathogenic to obligate mutualistic organisms. Both biotic and abiotic factors can influence species composition and structure of the insect gut bacterial communities. Dendroctonus valens is a destructive forest pest in China. To overcome host pine defenses, beetles mass-attack the pine to a threshold density that can exhaust pine defenses. The intensity of pine chemical defenses and carbohydrate concentrations of pines can be influenced by beetle attack, both of which are known factors that modify beetle’s gut microbiota. However, little is known to what extent variation exists in the beetle’s gut communities, and host monoterpenes and carbohydrates at different attack densities. In this study, the gut bacterial microbiota of D. valens at low and high attack densities were analyzed, and monoterpenes and carbohydrates in host pine phloem were assayed in parallel. The results showed that no significant changes of gut bacterial communities of the beetles and concentrations of D-glucose, D-pinitol, and D-fructose in pine phloem were found between low and high attack densities. The concentrations of α-pinene, β-pinene, limonene at high attack densities were significantly higher than those at low attack densities. Our results suggested that different attack densities of D. valens influence monoterpenes concentration of host pines’ phloem but have no significant impact on gut bacterial community structures of D. valens and carbohydrate concentration of host trees’ phloem in early attack phase. Similar gut bacterial community structures of D. valens between low and high attack densities might be due to the quick adaptation of gut microbiota to high monoterpenes concentrations. [ABSTRACT FROM AUTHOR]

Abstract: Plants engage in multiple root symbioses that offer varying degrees of benefit. We asked how variation in partner quality persists using a resource‐ratio model of population growth. We considered the plant's ability to preferentially allocate carbon to mutualists and competition for plant carbon between mutualist and nonmutualist symbionts. We treated carbon as two nutritionally interchangeable, but temporally separated, resources—carbon allocated indiscriminately for the construction of the symbiosis, and carbon preferentially allocated to the mutualist after symbiosis establishment and assessment. This approach demonstrated that coexistence of mutualists and nonmutualists is possible when fidelity of the plant to the mutualist and the cost of mutualism mediate resource competition. Furthermore, it allowed us to trace symbiont population dynamics given varying degrees of carbon allocation. Specifically, coexistence occurs at intermediate levels of preferential allocation. Our findings are consistent with previous empirical studies as well the application of biological market theory to plantroot symbioses. [ABSTRACT FROM AUTHOR]

Abstract: Animal movement is multidimensional and complex, and to understand the motor system of wild animals in the context of their natural ecology, we must analyse how suites of performance traits both mutualistically and antagonistically affect function—a necessity highlighted by previous work on performance trade‐offs. Evidence from some studies of human athletes using multidimensional analyses of performance suggests that overall quality among individuals can mask functional trade‐offs within them, yet no studies have tested this idea using wild animals. In this study, we investigated the possible mutualistic and antagonistic associations among eight different whole‐animal performance traits in male and female northern quolls (Dasyurus hallucatus). We detected trade‐offs between pairs of performance traits when conducted on raw standardized data using both Pearson product moment correlations and partial correlation analyses. For example, grasp strength was negatively associated with beam‐running speed using both analyses, suggesting that morphological designs that enhance grasp strength simultaneously compromise an animal's motor control or stability on a narrow beam. In addition, we detected a trade‐off between two distinct sets of performance traits; grasp strength, bite force and maximum oxygen consumption were negatively associated with jump acceleration and beam‐running speed. This trade‐off between sets of performance traits accounted for around one‐third of the total variance in performance among individuals and was primarily driven by the effects of body size on both groups of traits. Larger body sizes improved grasp strength, bite forces and maximum oxygen consumption rates but decreased jump accelerations and beam‐running speeds. Because the first component of a principal component analysis based on all eight performance traits (PCP1) did not load in the same direction for all traits, PCP1 did not represent an overall metric of motor performance—which differs from previous multivariate analyses of human physical performance. Our study highlights the importance of studying suites of traits when exploring the functional phenotype of organisms rather than just one or two dimensions of performance. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

In the present paper, we study a model with two symbiotic species, where one of the species is subject to disease infection. We observe that for increasing mutualism, the system may become unbounded. We also perform sensitivity analysis to identify the sensitive parameters of the model. Further, we incorporate incubation delay in the disease transmission and investigate how the qualitative behavior of the system changes for the incubation delay. We analyze the model with the help of stability and bifurcation analysis. Taking time-delay as bifurcation parameter, Hopfbifurcation and direction of Hopf-bifurcation are investigated near the coexistence equilibrium point. We illustrate analytical findings through numerical simulations. [ABSTRACT FROM AUTHOR]

Ever since May theorized that communities with larger numbers of species or interspecific interactions are inherently unstable, the mechanism allowing for the stable existence of complex communities in nature has been a central question in ecology. The main efforts to answer this question have sought to identify non-random features of ecological systems that can reverse a negative complexity-stability relationship into a positive one, but are far from successful, especially in their generality. Here, using the traditional community matrix analysis, we show that variation in the density dependence of interspecific interactions, which should be ubiquitous in nature, can dramatically affect the complexity-stability relationship. More specifically, we reveal that a positive complexity-stability relationship arises when harmful interspecific effects have larger density dependence than beneficial ones, regardless of the signs (i.e. positive or negative) of their dependence. Furthermore, numerical simulations demonstrated the synergistic stabilizing effect of interaction type diversity and density-dependence variation. Thus, this concept of density-dependence variation advances our understanding of the complexity-stability relationship in the real world. [ABSTRACT FROM AUTHOR]

Abstract: To elucidate fungicultural specializations contributing to ecological dominance of leafcutter ants, we estimate the phylogeny of fungi cultivated by fungus‐growing (attine) ants, including fungal cultivars from (i) the entire leafcutter range from southern South America to southern North America, (ii) all higher‐attine ant lineages (leafcutting genera Atta, Acromyrmex; nonleafcutting genera Trachymyrmex, Sericomyrmex) and (iii) all lower‐attine lineages. Higher‐attine fungi form two clades, Clade‐A fungi (Leucocoprinus gongylophorus, formerly Attamyces) previously thought to be cultivated only by leafcutter ants, and a sister clade, Clade‐B fungi, previously thought to be cultivated only by Trachymyrmex and Sericomyrmex ants. Contradicting this traditional view, we find that (i) leafcutter ants are not specialized to cultivate only Clade‐A fungi because some leafcutter species ranging across South America cultivate Clade‐B fungi; (ii) Trachymyrmex ants are not specialized to cultivate only Clade‐B fungi because some Trachymyrmex species cultivate Clade‐A fungi and other Trachymyrmex species cultivate fungi known so far only from lower‐attine ants; (iii) in some locations, single higher‐attine ant species or closely related cryptic species cultivate both Clade‐A and Clade‐B fungi; and (iv) ant–fungus co‐evolution among higher‐attine mutualisms is therefore less specialized than previously thought. Sympatric leafcutter ants can be ecologically dominant when cultivating either Clade‐A or Clade‐B fungi, sustaining with either cultivar‐type huge nests that command large foraging territories; conversely, sympatric Trachymyrmex ants cultivating either Clade‐A or Clade‐B fungi can be locally abundant without achieving the ecological dominance of leafcutter ants. Ecological dominance of leafcutter ants therefore does not depend primarily on specialized fungiculture of L. gongylophorus (Clade‐A), but must derive from ant–fungus synergisms and unique ant adaptations. [ABSTRACT FROM AUTHOR]

Cooperative interactions among species, termed mutualisms, have played a crucial role in the evolution of life on Earth. However, despite key potential benefits to partners, there are many cases in which two species cease to cooperate and mutualisms break down. What factors drive the evolutionary breakdown of mutualism? We examined the pathways toward breakdowns of the mutualism between plants and arbuscular mycorrhizal fungi. By using a comparative approach, we identify ~25 independent cases of complete mutualism breakdown across global seed plants. We found that breakdown of cooperation was only stable when host plants (i) partner with other root symbionts or (ii) evolve alternative resource acquisition strategies. Our results suggest that key mutualistic services are only permanently lost if hosts evolve alternative symbioses or adaptations. [ABSTRACT FROM AUTHOR]

Mutualisms between ophiostomatoid fungi and arthropods have been well documented. These fungi commonly aid arthropod nutrition and, in turn, are transported to new niches by these arthropods. The inflorescences of Protea trees provide a niche for a unique assemblage of ophiostomatoid fungi. Here, mites feed on Sporothrix fungi and vector the spores to new niches. Protea-pollinating beetles transport the spore-carrying mites between Protea trees. However, many Protea species are primarily pollinated by birds that potentially play a central role in the Protea-Sporothrix-mite system. To investigate the role of birds in the movement of mites and/or fungal spores, mites were collected from Protea inflorescences and cape sugarbirds, screened for Sporothrix fungal spores and tested for their ability to feed and reproduce on the fungal associates. Two mite species where abundant in both Protea inflorescences and on cape sugarbirds and regularly carried Sporothrix fungal spores. One of these mite species readily fed and reproduced on its transported fungal partner. For dispersal, this mite (a Glycyphagus sp.) attached to a larger mite species (Proctolaelaps vandenbergi) which, in turn, were carried by the birds to new inflorescences. The results of this study provide compelling evidence for a new mite-fungus mutualism, new mite-mite commensalisms and the first evidence of birds transporting mites with Sporothrix fungal spores to colonise new Protea trees. [ABSTRACT FROM AUTHOR]

Abstract: For a mutualism to remain evolutionarily stable, theory predicts that mutualists should limit their associations to high‐quality partners. However, most mutualists either simultaneously or sequentially associate with multiple partners that confer the same type of reward. By viewing mutualisms through the lens of niche breadth evolution, we outline how the environment shapes partner availability and relative quality, and ultimately a focal mutualist's partner breadth. We argue that mutualists that associate with multiple partners may have a selective advantage compared to specialists for many reasons, including sampling, complementarity, and portfolio effects, as well as the possibility that broad partner breadth increases breadth along other niche axes. Furthermore, selection for narrow partner breadth is unlikely to be strong when the environment erodes variation in partner quality, reduces the costs of interacting with low‐quality partners, spatially structures partner communities, or decreases the strength of mutualism. Thus, we should not be surprised that most mutualists have broad partner breadth, even if it allows for ineffective partners to persist. [ABSTRACT FROM AUTHOR]

Literature covered: early 2000s to late 2017 Bacteria frequently exchange metabolites with other micro- and macro-organisms. In these often obligate cross-feeding interactions, primary metabolites such as vitamins, amino acids, nucleotides, or growth factors are exchanged. The widespread distribution of this type of metabolic interactions, however, is at odds with evolutionary theory: why should an organism invest costly resources to benefit other individuals rather than using these metabolites to maximize its own fitness? Recent empirical work has shown that bacterial genotypes can significantly benefit from trading metabolites with other bacteria relative to cells not engaging in such interactions. Here, we will provide a comprehensive overview over the ecological factors and evolutionary mechanisms that have been identified to explain the evolution and maintenance of metabolic mutualisms among microorganisms. Furthermore, we will highlight general principles that underlie the adaptive evolution of interconnected microbial metabolic networks as well as the evolutionary consequences that result for cells living in such communities. [ABSTRACT FROM AUTHOR]