Extrafloral-nectar-based partner manipulation in plant-ant relationships

Neighbors sharing pathogens: the intricate relationship between Apis mellifera and ants (Hymenoptera: Formicidae) nesting in hives

Ants are ubiquitous and eusocial insects that exhibit frequent physical contact among colony members, thereby increasing their susceptibility to diseases. Some species are often found in beehives and in their surroundings, where they exploit the food resources of honey bees. This intricate relationship may facilitate the interspecific transmission of honey bee pathogens to ants, although ants themselves may contribute to spillback phenomena. The objective of this study was to assess the presence and abundance of honey bee pathogens in ants sampled from Italian apiaries. A total of 37 colonies within 24 apiaries across 7 regions were monitored. In total, 6 pathogens were detected in adult ants and 3 in the brood. In particular, the study revealed a high prevalence of honey bee pathogens in ants, with DWV, BQCV, and CBPV being the most commonly encountered. The brood also tested positive for the same viruses. Notably, all analyzed viruses were found to be replicative in both adult ants and ant broods. Furthermore, co-infections were prevalent, suggesting complex pathogen interactions within ant populations. Statistical analysis indicated significant differences in pathogen prevalence and abundance among ant species and sample types. The findings highlight active infection in both the ants and the brood, suggesting a potential role of ants as reservoir hosts and vectors of honey bee pathogens emphasizing the need for further research to understand the implications of interspecific pathogen transmission on ant and bee health.

Manipulated ants: inducing loyalty to sugar feeders with an alkaloid

BACKGROUND

Wood ants are promising biocontrol agents in fruit plantations because they prey on pest insects and inhibit plant diseases. However, these ants also attend plant-feeding homopterans to harvest their honeydew secretions, thereby increasing their numbers. This problem can be solved by offering ants alternative sugar sources that are more attractive than honeydew. From natural interactions, it is known that some species manipulate mutualistic partners toward loyalty by adding alkaloids to the food they offer their mutualists. Inspired by this, the addition of alkaloids might be used to make ants loyal to artificial sugar feeders and thus used to reduce populations of ant-farmed homopterans in ant-mediated biological control. We aimed to explore whether wood ants (Formica polyctena) would develop a taste preference for morphine-containing sugar solutions in two-choice laboratory tests.

RESULTS

After having fed on a morphine/sugar solution for 1 week, ants showed a significant preference for morphine solutions compared with equal concentration sugar solutions without morphine. Furthermore, ants lost this preference after 6-9 days on a morphine-free diet.

CONCLUSION

The results show that wood ants react to morphine in their food, enabling chemical manipulation of their behavior, most likely through a taste preference. Thus, ants are susceptible to manipulation by mutualistic partners in natural interactions and furthermore may be manipulated artificially in biocontrol programs to avoid ant-mediated build-up of homopteran populations. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Plant Reproductive Success Mediated by Nectar Offered to Pollinators and Defensive Ants in Terrestrial Bromeliaceae

Most plants produce floral nectar to attract pollinators that impact pollination and seed production; some of them also secrete extrafloral nectar harvested by insects that may influence the plant reproductive success. The aim of this study was to analyze the effects of excluding pollinators and/or ants on the per-plant reproductive success in two species (Dyckia floribunda Griseb. and Dyckia longipetala Baker, Bromeliaceae) that produce floral and extrafloral nectar. The hypothesis states that both ecological processes (pollination and ant defense) involving nectar-mediated animal-plant interactions are beneficial for plant reproductive success. We expected the highest decrease in the plant fruit and seed sets when the pollinators and ants were excluded, and a moderate decrease when solely ants were excluded, compared to the control plants (those exposed to pollinators and ants). In addition, a lower natural reproductive success was also expected in the self-incompatible D. longipetala than in the self-compatible D. floribunda, as the former totally depends on animal pollination for seed production. D. floribunda and D. longipetala presented similar trends in the response variables, and the expected results for the experimental treatments were observed, with some variations between species and among populations. The ecological function of nectar is important because these two plant species depend on pollinators to produce seeds and on ants to defend flowers from the endophytic larvae of Lepidoptera. The study of multispecies interactions through mechanistic experiments could be necessary to clarify the specific effects of different animals on plant reproductive success.

Isolation, characterization and screening of actinomycetes associated with fijian ant-plant symbioses

In the search for novel therapeutics to combat the ongoing antimicrobial resistance crisis, scientists are turning to underexplored environments. Defensive mutualisms between hymenopteran insects and actinomycetes represent important reservoirs for bioactive compounds. In this study, we examined the association between actinomycetes and Squamellaria ant-plants spanning three different ant and plant species combinations (Squamellaria imberbis-Philidris nagasau, Squamellaria tenuiflora- Technomyrmex vitiensis, and Squamellaria tenuiflora-Tetramorium insolens). Eight Squamellaria plants were sampled including four containing T. vitiensis, three containing P. nagasau, and a single plant containing T. insolens. A total of 47 actinomycetes were obtained from the sampled material, with 5, 16, and 26 isolates originating from cuticle, tissue, and nest samples, respectively. Cross-streaking tests showed that 12 out of 47 isolates inhibited bacterial pathogens. The most frequently inhibited pathogens in the cross-streaking tests were S. aureus and E. coli while S. enterica was the least inhibited. Among the three primary screening media used, ISP2 agar was the most suitable for secondary metabolism as more isolates exhibited antibacterial activity when grown on the medium. TFS2010 and TFS2003, which matched to Streptomyces gramineus (>99% similarity), were the most bioactive isolates in cross-streaking tests. TFS2010 displayed the strong antibacterial on Nutrient agar, Mueller Hinton agar, and ISP2 agar while TFS2003 only exhibited strong antibacterial activity on Nutrient agar. Furthermore, a difference in potency of extracts based on batch culture medium was noted in TFS2010. DNA was extracted from 19 isolates and followed by 16SrRNA gene sequencing. Analysis of sequence data revealed the presence of six genera, including Amycolatopsis, Asanoa, Jiangella, Nocardia, Nocardiopsis, and Streptomyces, with the latter being the most abundant taxon. Among these, three isolates (PNS3002, PNS3005, and TFS3001) are likely to represent new species while one (TFS2015) is likely to be a member of a novel genus. Our work represents the first attempt to study actinomycetes from Squamellaria-ant mutualisms.

Inaugural Description of Extrafloral Nectaries in Sapindaceae: Structure, Diversity and Nectar Composition

Sapindales is a large order with a great diversity of nectaries; however, to date, there is no information about extrafloral nectaries (EFN) in Sapindaceae, except recent topological and morphological data, which indicate an unexpected structural novelty for the family. Therefore, the goal of this study was to describe the EFN in Sapindaceae for the first time and to investigate its structure and nectar composition. Shoots and young leaves of Urvillea ulmacea were fixed for structural analyses of the nectaries using light and scanning electron microscopy. For nectar composition investigation, GC-MS and HPLC were used, in addition to histochemical tests. Nectaries of Urvillea are circular and sunken, corresponding to ocelli. They are composed of a multiple-secretory epidermis located on a layer of transfer cells, vascularized by phloem and xylem. Nectar is composed of sucrose, fructose, xylitol and glucose, in addition to amino acids, lipids and phenolic compounds. Many ants were observed gathering nectar from young leaves. These EFNs have an unprecedented structure in the family and also differ from the floral nectaries of Sapindaceae, which are composed of secretory parenchyma and release nectar through stomata. The ants observed seem to protect the plant against herbivores, and in this way, the nectar increases the defence of vegetative organs synergistically with latex.

An experimental, behavioral, and chemical analysis of food limitations in mutualistic Crematogaster ant symbionts inhabiting Macaranga host plants

Obligate mutualistic plant-ants are often constrained by their plant partner's capacity to provide resources. However, despite this limitation, some ant partners actively reject potential prey items and instead drop them from the plant rather than consuming them, leaving the ants entirely reliant on host plant-provided food, including that provided indirectly by the symbiotic scale insects that ants tend inside the plants. This dependency potentially increases the efficiency of these ants in defending their host. We hypothesize that if this ant behavior was beneficial to the symbiosis, prey rejection by ants would be observed across multiple plant host species. We also hypothesize that plant-provided food items and symbiotic scale insects from other ant plants should be rejected. We address these hypotheses in the Crematogaster ant-Macaranga plant system, in which plants provide living space and food, while ants protect plants from herbivory. We observed food acceptance and rejection behavior across five ant species and three plant host species. Ants were offered three types of food: termites as a surrogate herbivore, symbiotic scale insects, and nutritious food bodies (FB) produced by different host plant species. The unique ant species living in M. winkleri was the most likely to reject food items not provided by the plant species, followed by ants in M. glandibracteolata, while ants in M. pearsonii accepted most items offered to them. Using stable isotopes, chemical cues, and proteomic analyses, we demonstrate that this behavior was not related to differences between plant species in nutritional quality or composition of FB. Isotopic signatures revealed that certain species are primary consumers but other ant species can be secondary consumers even where surrogate herbivores are rejected, although these values varied depending on the ant developmental stage and plant species. Macaranga pearsonii and M. glandibracteolata, the two most closely related plant species, had most similar surface chemical cues of FB. However, M. glandibracteolata had strongest differences in food body nutritional content, isotopic signatures, and protein composition from either of the other two plant species studied. Taken together we believe our results point toward potential host coercion of symbiont ants by plants in the genus Macaranga Thouars (Euphorbiaceae).

Effects of conventional and organic management on plant and insect communities in a traditional elephant garlic crop

Agricultural management has a great influence on biodiversity and its services in agroecosystems. In Europe, a relevant proportion of biodiversity is dependent on low-input agriculture. To assess the effects of agricultural management on biodiversity, in this study we surveyed the communities of arable plants, diurnal flying insects, and pollinators in three conventional and in two organic fields of a traditional Elephant garlic (Allium ampeloprasum L.) crop of the Valdichiana area, in Tuscany (central Italy). The sampling was carried out twice during the season: in spring, during crop growing, and in summer, after crop harvesting. We assessed the effects of the different agricultural management on the richness and composition (species occurrence and abundance) of the three communities using univariate and multivariate analyses. Concerning our specific case study, only plant species richness was significantly higher in organic fields (15.7 ± 2.7 species per plot), compared to conventional ones (5.4 ± 2.3 species per plot). Regarding community composition, only pollinators showed a marginally significant difference between conventional and organic fields. Conversely, the effect of specific fields significantly explained differences in composition of all the investigated groups (plants, total insects, and pollinators). The results suggest that, in our case study, the emerged differences in diversity of the investigated communities were mainly attributable to environmental and management factors related to single fields, more than to organic or conventional farming. Such evidence could be partly due to the very local scale of the study, to the heterogeneity of the surveyed fields, and to the reduced number of surveyed fields. Further investigation is therefore needed.

Understanding interdisciplinary perspectives of plant intelligence: Is it a matter of science, language, or subjectivity?

BACKGROUND

Evidence suggests that plants can behave intelligently by exhibiting the ability to learn, make associations between environmental cues, engage in complex decisions about resource acquisition, memorize, and adapt in flexible ways. However, plant intelligence is a disputed concept in the scientific community. Reasons for lack of consensus can be traced back to the history of Western philosophy, interpretation of terminology, and due to plants lacking neurons and a central nervous system. Plant intelligence thus constitutes a novel paradigm in the plant sciences. Therefore, the perspectives of scientists in plant-related disciplines need to be investigated in order to gain insight into the current state and future development of this concept.

METHODS

This study analyzed opinions of plant intelligence held by scientists from different plant-related disciplines, including ethnobiology and other biological sciences, through an online questionnaire.

RESULTS

Our findings show that respondents' personal belief systems and the frequency of taking into account other types of knowledge, such as traditional knowledge, in their own field(s) of study, were associated with their opinions of plant intelligence. Meanwhile, respondents' professional expertise, background (discipline), or familiarity with evidence provided on plant intelligence did not affect their opinions.

CONCLUSIONS

This study emphasizes the influential role of scientists' own subjective beliefs. In response, two approaches could facilitate transdisciplinary understanding among scientists: (1) effective communication designed to foster change in agreement based on presented information; and (2) holding space for an interdisciplinary dialogue where scientists can express their own subjectivities and open new opportunities for collaboration.

Cornflower Honey as a Model for Authentication of Unifloral Honey Using Classical Methods Combined with Plant-Based Marker Substances Such as Lumichrome

According to legislation, unifloral honeys are characterized by their organoleptic, physicochemical, and microscopic properties. Melissopalynology is the established method for identifying the pollen taken up with the floral nectar by forager bees and is used for authentication of the nectar sources in honey. For cornflower honey (Centaurea cyanus), the pollen input does not correlate with the nectar input, because the nectar is produced both in floral and in extrafloral nectaries. The well-known cornflower marker lumichrome has now also been detected in the extrafloral nectar. Therefore, lumichrome is a suitable marker substance for cornflower honey. Four different methods for the sole analysis of lumichrome in honey were validated and compared. Studies over nine years have shown that unifloral cornflower honey should contain approximately 35 mg/kg lumichrome. For a further differentiated cornflower honey specific verification, other nonvolatile compounds like 7-carboxylumichrome and volatiles, such as 3,4-dihydro-3-oxoedulan I and 3,4-dihydro-3-oxoedulan II, should be analyzed. This enables a more specific accuracy for the classification of unifloral cornflower honey.

Consciousness and cognition in plants

Unlike animal behavior, behavior in plants is traditionally assumed to be completely determined either genetically or environmentally. Under this assumption, plants are usually considered to be noncognitive organisms. This view nonetheless clashes with a growing body of empirical research that shows that many sophisticated cognitive capabilities traditionally assumed to be exclusive to animals are exhibited by plants too. Yet, if plants can be considered cognitive, even in a minimal sense, can they also be considered conscious? Some authors defend that the quest for plant consciousness is worth pursuing, under the premise that sentience can play a role in facilitating plant's sophisticated behavior. The goal of this article is not to provide a positive argument for plant cognition and consciousness, but to invite a constructive, empirically informed debate about it. After reviewing the empirical literature concerning plant cognition, we introduce the reader to the emerging field of plant neurobiology. Research on plant electrical and chemical signaling can help shed light into the biological bases for plant sentience. To conclude, we shall present a series of approaches to scientifically investigate plant consciousness. In sum, we invite the reader to consider the idea that if consciousness boils down to some form of biological adaptation, we should not exclude a priori the possibility that plants have evolved their own phenomenal experience of the world. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Philosophy > Consciousness Neuroscience > Cognition.

Individuality, self and sociality of vascular plants

Vascular plants are integrated into coherent bodies via plant-specific synaptic adhesion domains, action potentials (APs) and other means of long-distance signalling running throughout the plant bodies. Plant-specific synapses and APs are proposed to allow plants to generate their self identities having unique ways of sensing and acting as agents with their own goals guiding their future activities. Plants move their organs with a purpose and with obvious awareness of their surroundings and require APs to perform and control these movements. Self-identities allow vascular plants to act as individuals enjoying sociality via their self/non-self-recognition and kin recognition. Flowering plants emerge as cognitive and intelligent organisms when the major strategy is to attract and control their animal pollinators as well as seed dispersers by providing them with food enriched with nutritive and manipulative/addictive compounds. Their goal in interactions with animals is manipulation for reproduction, dispersal and defence. This article is part of the theme issue 'Basal cognition: multicellularity, neurons and the cognitive lens'.

First Report on the Acrobat Ant Crematogaster scutellaris Storing Live Aphids in Its Oak-Gall Nests

Simple Summary

Galls represent an amazing microcosm which contains a variety of multiple interactions among different actors, and therefore, offers the opportunity to observe and investigate phenomena belonging to different areas of biology: from the development process, connected to the interaction between the galligenous agent and the host plant, to the moment of their colonization by different species, since some ants may provide defense against pathogens, certain phytophagous insects or favor mutualists. In the present work we describe some aspects of oak-gall colonization by different ant species, highlighting how the gall’s height on the plant influences ant colonization and how different ant species produce different nest architectures. The most relevant aspect, however, is the discovery of a novel ant-aphid relationship: the transport of living aphids into oak-gall nests. We found no evidence of immediate predation of these aphids inside the galls, so they are likely stored to overwinter due to a mutualistic relationship and/or serve as food storage. This is not only an interesting report on the mutualisms involving ants and their insect partners, but it may also have important consequences on the aphids’ phenology with the host plants. Once more, ants show their relevant impact on multitrophic interactions and ecosystem dynamics.

Abstract

This study provides new data about the role of ants in mutualistic interactions with aphids mediated by galls. We focused our investigation on galls induced by the cynipid Andricus kollari by conducting a survey and a subsequent experiment in an Italian oak forest. The ants Crematogaster scutellaris, Colobopsis truncata and Temnothorax italicus frequently used the galls as nests: Crematogaster scutellaris occupied galls which were located higher on the oak trees, while C. truncata and T. italicus were located at lower positions. In addition, galls occupied by C. scutellaris showed varied internal architecture in relation to the colony composition. Importantly, field surveys revealed for the first time that C. scutellaris nest galls also contained live individuals of the non-galligenous aphid Panaphis juglandis. Field experiments suggested that the ants actively seek, collect and stock live aphids. No signs of predation and injuries were detected on the stored aphids, which were probably kept for safe overwintering, though we cannot exclude a possible occasional use as food. This report reveals a possible novel relationship which could have important consequences on the phenology and presence of aphids on the host plant.

Altered feeding behavior and immune competence in paper wasps: A case of parasite manipulation?

Paper wasps (Polistes dominula), parasitized by the strepsipteran Xenos vesparum, are castrated and desert the colony to gather on plants where the parasite mates and releases primary larvae, thus completing its lifecycle. One of these plants is the trumpet creeper Campsis radicans: in a previous study the majority of all wasps collected from this plant were parasitized and focused their foraging activity on C. radicans buds. The unexpected prevalence and unusual feeding strategy prompted us to investigate the influence of this plant on wasp behavior and physiology through a multidisciplinary approach. First, in a series of laboratory bioassays, we observed that parasitized wasps spent more time than non-parasitized ones on fresh C. radicans buds, rich of extra-floral nectaries (EFNs), while the same wasps ignored treated buds that lacked nectar drops. Then, we described the structure and ultra-structure of EFNs secreting cells, compatible with the synthesis of phenolic compounds. Subsequently, we analysed extracts from different bud tissues by HPLC-DAD-MS and found that verbascoside was the most abundant bioactive molecule in those tissues rich in EFNs. Finally, we tested the immune-stimulant properties of verbascoside, as the biochemical nature of this compound indicates it might function as an antibacterial and antioxidant. We measured bacterial clearance in wasps, as a proxy for overall immune competence, and observed that it was enhanced after administration of verbascoside-even more so if the wasp was parasitized. We hypothesize that the parasite manipulates wasp behavior to preferentially feed on C. radicans EFNs, since the bioactive properties of verbascoside likely increase host survival and thus the parasite own fitness.

Plant behaviour: an evolutionary response to the environment?

Plants are not just passive living beings that exist in nature. They are complex and highly adaptable species that react sensitively to environmental forces/stimuli with movement, morphological changes and through the communication via volatile molecules. In a way, plants mimic some traits of animal and human behaviour; they compete for limited resources by gaining more area for more sunlight and spread their roots underground. Furthermore, in order to survive and thrive, they evolve and 'learn' to control various environmental stress factors in order to increase the yield of flowering, fertilization and germination processes. The concept of associating complex behaviour, such as intelligence, with plants is still a highly debatable topic among researchers worldwide. Recent studies have shown that plants are able to discriminate between positive and negative experiences and 'learn' from them. Some botanists have interpreted these behavioural data as a form of primitive cognitive processes. Others have evaluated these responses as biological automatisms of plants determined by adaptation to the environment and absence of intelligence. This review aims to explore adaptive behavioural aspects of various plant species distributed in different ecosystems by emphasizing their biological complexity and survival instincts.

New Tools for Conservation Biological Control: Testing Ant-Attracting Artificial Nectaries to Employ Ants as Plant Defenders

Knowledge of the role of ants in many agroecosystems is relatively scarce, and in temperate regions the possibility to exploit ants as biocontrol agents for crop protection is still largely unexplored. Drawing inspiration from mutualistic ant–plant relationships mediated by extrafloral nectaries (EFNs), we tested the use of artificial nectaries (ANs) in order to increase ant activity on pear trees and to evaluate the effects on the arthropods, plant health and fruit production. While EFNs secrete a complex solution mainly composed of sugars and amino acids, ANs were filled with water and sucrose only. The results suggest that ANs can be used as manipulative instruments to increase ant activity over long periods of time. High ant activity was significantly linked to lower incidence of the pathogen fungus Venturia pyrina (pear scab) on pear leaves, and of the presence of Cydia pomonella (codling moth) caterpillars on pear fruit production. These results further encourage exploring underrated possibilities in the development of new tools for conservation biological control (CBC).

Trade-off in plant-ant interactions: seasonal variations

This work evaluated the effect of seasonality on ant-plant interaction in a Seasonally Dry Tropical Forests, using as an ecological model the species Ipomoea carnea subs. fistulosa (Convolvulaceae). We performed systematic collection of ants, herbivores and leaves in marked plants, evaluated the efficiency of herbivorous capture by ants, and the effects of ant presence over the pollinator behavior and plant fitness in dry and rainy seasons. The presence of ants in the plants reduced the number of herbivores (dry season: F2.27=4.7617, p=0.0166; rainy season: F2.27=5.8655, p=0.0078). However, the capture efficiency was negatively affected by the presence of myrmecophilous larvae, so that the average of ants recruited on termite leaves was 2.06 ants per termite, the average recruitment of ants on larval leaves was 22.4 larva ants. In addition, the presence of ants reduced pollinator visits and promoted fruit reduction during the dry season (ANOVA: F = 3.44; p = 0.0653). In conclusion, the association with ants can result in a balance not always favorable to the host plant, and this result actually depends on abiotic (e.g. precipitation) and biotic factors (e.g. ant species composition and abundance, influence of other trophic levels and identity of associated herbivores).

Functional Role of Extrafloral Nectar in Boreal Forest Ecosystems under Climate Change

Carbohydrate-rich extrafloral nectar (EFN) is produced in nectaries on the leaves, stipules, and stems of plants and provides a significant energy source for ants and other plant mutualists outside of the flowering period. Our review of literature on EFN indicates that only a few forest plant species in cool boreal environments bear EFN-producing nectaries and that EFN production in many boreal and subarctic plant species is poorly studied. Boreal forest, the world’s largest land biome, is dominated by coniferous trees, which, like most gymnosperms, do not produce EFN. Notably, common deciduous tree species that can be dominant in boreal forest stands, such as Betula and Alnus species, do not produce EFN, while Prunus and Populus species are the most important EFN-producing tree species. EFN together with aphid honeydew is known to play a main role in shaping ant communities. Ants are considered to be keystone species in mixed and conifer-dominated boreal and mountain forests because they transfer a significant amount of carbon from the canopy to the soil. Our review suggests that in boreal forests aphid honeydew is a more important carbohydrate source for ants than in many warmer ecosystems and that EFN-bearing plant species might not have a competitive advantage against herbivores. However, this hypothesis needs to be tested in the future. Warming of northern ecosystems under climate change might drastically promote the invasion of many EFN-producing plants and the associated insect species that consume EFN as their major carbohydrate source. This may result in substantial changes in the diet preferences of ant communities, the preventative roles of ants against insect pest outbreaks, and the ecosystem services they provide. However, wood ants have adapted to using tree sap that leaks from bark cracks in spring, which may mitigate the effects of improved EFN availability.

Gall-Colonizing Ants and Their Role as Plant Defenders: From 'Bad Job' to 'Useful Service'

Galls are neoformed structures on host plant tissues caused by the attack of insects or other organisms. They support different communities of specialized parasitic insects (the gall inducers), and can also provide refuge to other insects, such as moths, beetles and ants, referred to as secondary occupants. This study focuses on galls induced by the oak gall wasp Andricus quercustozae and secondarily colonized by ants in a mixed oak forest. A field survey and two experiments were carried out to a) study ant (species-specific) preferences for different features of the galls, b) describe differences in gall architecture due to ant activity, c) analyse the effects of the presence of gall-dwelling ants on plant health. The results show that there are differences between ant species in gall colonization and in the alteration of gall opening and inner structure. We verified that gall-dwelling ants protect their host plants efficiently, offering them an indirect defence mechanism against enemies (predators and pathogens). The data suggest a new paradigm in ant–plant relationships mediated by the presence of galls on the plants whose ecological and evolutionary implications are discussed.

Extrafloral nectary-bearing plant Mallotus japonicus uses different types of extrafloral nectaries to establish effective defense by ants

Extrafloral nectary (EFN)-bearing plants attract ants to gain protection against herbivores. Some EFN-bearing plants possess different types of EFNs, which might have different effects on ants on the plants. Mallotus japonicus (Thunb.) Muell. Arg. (Euphorbiaceae) bears two types of EFNs, including a pair of large EFNs at the leaf base and many small EFNs along the leaf edge. This study aimed to determine the different roles of the two types of EFNs in biotic defense by ants. A field experiment was conducted to investigate the effect of leaf damage on EFN production and on the distribution pattern of ants. After leaf damage, the number of leaf edge EFNs increased in the leaves first-produced. The number of ants on the leaves also increased, and the foraging area of ants extended from the leaf base to the leaf tip. An EFN-covering field experiment revealed that leaf edge EFNs had a greater effect than leaf base EFNs on ant dispersal on leaves. The extended foraging area of ants resulted in an increase of encounter or attack rate against an experimentally placed herbivore, Spodoptera litura. These results suggest that M. japonicus plants control the foraging area of ants on their leaves using different types of EFNs in response to leaf damage, thus achieving a very effective biotic defense against herbivores by ants.

Origanum vulgare terpenoids modulate Myrmica scabrinodis brain biogenic amines and ant behaviour

Coordinated social behaviour is fundamental for ant ecological success. However, even distantly-related organisms, such as plants, have evolved the ability to manipulate ant collective performances to their own advantage. In the parasitic system encompassing Maculinea butterflies, Myrmica ants, and Origanum vulgare plants, the ant-plant interaction elicits the release of a volatile terpenoid compound (carvacrol) which is used by the gravid butterfly to locate the ideal oviposition site. Here we show that this ant-plant association is maintained by the effect of O. vulgare terpenoids on ant behaviour and that food plants might gain protection by Myrmica ants by chemically manipulating workers to forage in their surroundings. The variation in the locomotor ability of three ant species (Formica cinerea, Tetramorium caespitum, and Myrmica scabrinodis) was studied after treatment with the two major O. vulgare terpenoid volatile compounds (i.e., carvacrol and thymol). The brain levels of three biogenic amines (dopamine, tyramine and serotonin) were analysed in ants exposed to the O. vulgare terpenoids by HPLC-ESI-MS/MS. Carvacrol and thymol increased the locomotor activity of all ant species tested, but if blended reduced the movement propensity of Myrmica scabrinodis. Dopamine and tyramine production was positively correlated with the worker locomotor activity. In Myrmica ants, both brain biogenic ammines were negatively correlated with the aggressive behaviour. Blends of O. vulgare volatiles affected the locomotor ability while increased the aggressiveness of Myrmica workers by altering the aminergic regulation in the ant brains. This behavioural manipulation, might enhance partner fidelity and plant protection. Our findings provide new insights supporting a direct role of plant volatiles in driving behavioural changes in social insects through biogenic amine modulation.

Nectar in Plant-Insect Mutualistic Relationships: From Food Reward to Partner Manipulation

It has been known for centuries that floral and extra-floral nectar secreted by plants attracts and rewards animals. Extra-floral nectar is involved in so-called indirect defense by attracting animals (generally ants) that prey on herbivores, or by discouraging herbivores from feeding on the plant. Floral nectar is presented inside the flower close to the reproductive organs and rewards animals that perform pollination while visiting the flower. In both cases nectar is a source of carbon and nitrogen compounds that feed animals, the most abundant solutes being sugars and amino acids. Plant-animal relationships involving the two types of nectar have therefore been used for a long time as text-book examples of symmetric mutualism: services provided by animals to plants in exchange for food provided by plants to animals. Cheating (or deception or exploitation), namely obtaining the reward/service without returning any counterpart, is however, well-known in mutualistic relationships, since the interacting partners have conflicting interests and selection may favor cheating strategies. A more subtle way of exploiting mutualism was recently highlighted. It implies the evolution of strategies to maximize the benefits obtained by one partner while still providing the reward/service to the other partner. Several substances other than sugars and amino acids have been found in nectar and some affect the foraging behavior of insects and potentially increase the benefits to the plant. Such substances can be considered plant cues to exploit mutualism. Recent evidence motivated some authors to use the term "manipulation" of animals by plants in nectar-mediated mutualistic relationships. This review highlights the recent background of the "manipulation" hypothesis, discussing it in the framework of new ecological and evolutionary scenarios in plant-animal interactions, as a stimulus for future research.

Influences of Species Interactions With Aggressive Ants and Habitat Filtering on Nest Colonization and Community Composition of Arboreal Twig-Nesting Ants

Ant community assembly is driven by many factors including species interactions (e.g., competition, predation, parasitism), habitat filtering (e.g., vegetation differences, microclimate, food and nesting resources), and dispersal. Canopy ant communities, including dominant and twig-nesting ants, are structured by all these different factors, but we know less about the impacts of species interactions and habitat filters acting at the colonization or recruitment stage. We examined occupation of artificial twig nests placed in shade trees in coffee agroecosystems. We asked whether species interactions-aggression from the dominant canopy ant, Azteca sericeasur Longino (Hymenoptera: Formicidae)-or habitat filtering-species of tree where nests were placed or surrounding vegetation-influence colonization, species richness, and community composition of twig-nesting ants. We found 20 species of ants occupying artificial nests. Nest occupation was lower on trees with A. sericeasur, but did not differ depending on tree species or surrounding vegetation. Yet, there were species-specific differences in occupation depending on A. sericeasur presence and tree species. Ant species richness did not vary with A. sericeasur presence or tree species. Community composition varied with A. sericeasur presence and surrounding vegetation. Our results suggest that species interactions with dominant ants are important determinants of colonization and community composition of twig-nesting ants. Habitat filtering at the level of tree species did not have strong effects on twig-nesting ants, but changes in coffee management may contribute to differences in community composition with important implications for ant conservation in agricultural landscapes, as well as biological control of coffee pests.

Pericarpial nectary-visiting ants do not provide fruit protection against pre-dispersal seed predators regardless of ant species composition and resource availability

Extrafloral nectaries can occur in both vegetative and reproductive plant structures. In many Rubiaceae species in the Brazilian Cerrado, after corolla abscission, the floral nectary continues to secret nectar throughout fruit development originating post-floral pericarpial nectaries which commonly attract many ant species. The occurrence of such nectar secreting structures might be strategic for fruit protection against seed predators, as plants are expected to invest higher on more valuable and vulnerable parts. Here, we performed ant exclusion experiments to investigate whether the interaction with ants mediated by the pericarpial nectaries of Tocoyena formosa affects plant reproductive success by reducing the number of pre-dispersal seed predators. We also assessed whether ant protection was dependent on ant species composition and resource availability. Although most of the plants were visited by large and aggressive ant species, such as Ectatomma tuberculatum and species of the genus Camponotus, ants did not protect fruits against seed predators. Furthermore, the result of the interaction was neither related to ant species composition nor to the availability of resources. We suggest that these results may be related to the nature and behavior of the most important seed predators, like Hemicolpus abdominalis weevil which the exoskeleton toughness prevent it from being predated by most ant species. On the other hand, not explored factors, such as reward quality, local ant abundance, ant colony characteristics and/or the presence of alternative energetic sources could also account for variations in ant frequency, composition, and finally ant protective effects, highlighting the conditionality of facultative plant-ant mutualisms.

Introduction to the Special Issue: Beyond traits: integrating behaviour into plant ecology and biology

The way that plants are conceptualized in the context of ecological understanding is changing. In one direction, a reductionist school is pulling plants apart into a list of measured 'traits', from which ecological function and outcomes of species interactions may be inferred. This special issue offers an alternative, and more holistic, view: that the ecological functions performed by a plant will be a consequence not only of their complement of traits but also of the ways in which their component parts are used in response to environmental and social conditions. This is the realm of behavioural ecology, a field that has greatly advanced our understanding of animal biology, ecology and evolution. Included in this special issue are 10 articles focussing not on the tried and true metaphor that plant growth is similar to animal movement, but instead on how application of principles from animal behaviour can improve our ability to understand plant biology and ecology. The goals are not to draw false parallels, nor to anthropomorphize plant biology, but instead to demonstrate how existing and robust theory based on fundamental principles can provide novel understanding for plants. Key to this approach is the recognition that behaviour and intelligence are not the same. Many organisms display complex behaviours despite a lack of cognition (as it is traditionally understood) or any hint of a nervous system. The applicability of behavioural concepts to plants is further enhanced with the realization that all organisms face the same harsh forces of natural selection in the context of finding resources, mates and coping with neighbours. As these ecological realities are often highly variable in space and time, it is not surprising that all organisms-even plants-exhibit complex behaviours to handle this variability. The articles included here address diverse topics in behavioural ecology, as applied to plants: general conceptual understanding, plant nutrient foraging, root-root interactions, and using and helping others. As a group, the articles in this special issue demonstrate how plant ecological understanding can be enhanced through incorporation of behavioural ideas and set the stage for future research in the emerging discipline of plant behavioural ecology.