Ant-plant Mutualisms Research Articles

Species diversity and biological trait function: Effectiveness of ant–plant mutualism decreases as ant species diversity increases

Abstract One of the major concerns of ecological and evolutionary research is the prediction of community function in relation to the degree of biodiversity. To clarify the relationship between biodiversity and the expression of plant defence traits, we investigated ant–plant defensive mutualism in the pioneer plant Mallotus japonicus at several sites across Japan. The plant bears ant‐attracting extrafloral nectar (EFN) and food bodies (FBs) as indirect defence traits. To reveal variations in ant–plant interactions in the field, we measured species richness of nectar‐feeding ants and interaction strength between each ant species and the plant (visiting frequency of each ant species to the plant). We also investigated the expression of EFNs and FBs in natural plant populations at the study sites. To assess the defensive quality of each ant species, we then experimentally estimated the aggressiveness of the dominant ant species. To examine the link between ant species richness and the defensive function of ants, we conducted an ant‐exclusion experiment and a common garden experiment to clarify whether the defence efficacy of ants varied in relation to ant species richness. Ant species richness differed among the study sites. We found negative relationships between ant species richness and the mean interaction strength of ant species, the interaction strength of aggressive ant species and the number of EFNs per leaf. The effectiveness of indirect defence by ants was poor at sites where ant species richness was high. When cultivated in the same environment, plants from sites with low ant species richness developed a larger number of EFNs per leaf than those from sites with high ant species richness. Our results suggest that facultative ant–plant defensive mutualism is weakened at sites where ant species richness is high, resulting in a decrease in the number of EFNs per leaf. Such a link between species richness and an indirect trait function may help us to understand the evolutionary patterns of various species traits in complex biological communities. A free Plain Language Summary can be found within the Supporting Information of this article.

Nutrient provisioning of its host myrmecophytic tree by a temporary social parasite of a plant-ant

Abstract One of the most advanced ant–plant mutualisms is represented by myrmecophytes sheltering colonies of some plant-ant species in hollow structures called domatia. In turn, the myrmecophytes benefit from biotic protection and sometimes nutrient provisioning (myrmecotrophy). Furthermore, over the course of evolution, some ant species have become social parasites of others. In this general context, we studied the relationship between its host trees and Azteca andreae (Dolichoderinae), a temporary social parasite of the plant-ant Azteca ovaticeps, and, as such, obligatorily associated with myrmecophytic Cecropia obtusa trees (Urticaceae). A first experiment showed that the δ15N values of the young leaves of Cecropia sheltering a mature A. andreae colony were very similar to those for trees sheltering Azteca alfari or A. ovaticeps, two typical Cecropia mutualists for which myrmecotrophy is known. In a second experiment, by injecting a 15N-labelled glycine solution into locusts given as prey to A. andreae colonies, we triggered an increase in δ15N in the young leaves of their host Cecropia. Thus, 15N passed from the prey to the host trees, explaining the outcomes of the first experiment. We discuss these results in light of the notion of ‘by-product benefits’.

Consistent patterns of fungal communities within ant-plants across a large geographic range strongly suggest a multipartite mutualism

In recent decades, multipartite mutualisms involving microorganisms such as fungi have been discovered in associations traditionally thought of as bipartite. Ant-plant mutualisms were long thought to be bipartite despite fungi being noticed in an epiphytic ant-plant over 100 years ago. We sequenced fungal DNA from the three distinct domatium chambers of the epiphytic ant-plant Myrmecodia beccarii to establish if fungal communities differ by chamber type across five geographic locations spanning 675 km. The three chamber types serve different ant-associated functions including ‘waste’ chambers, where ant workers deposit waste; ‘nursery’ chambers, where the brood is kept; and ‘ventilation’ chambers, that allow air into the domatium. Overall, fungi from the order Chaetothyriales dominated the chambers in terms of the proportion of operational taxonomic units (OTUs; 13.4%) and sequence abundances of OTUs (28% of the total); however a large portion of OTUs (28%) were unidentified at the order level. Notably, the fungal community in the waste chambers differed consistently from the nursery and ventilation chambers across all five locations. We identified 13 fungal OTUs as ‘common’ in the waste chambers that were rare or in very low sequence abundance in the other two chambers. Fungal communities in the nursery and ventilation chambers overlapped more than either did with the waste chambers but were also distinct from each other. Differences in dominance of the common OTUs drove the observed patterns in the fungal communities for each of the chamber types. This suggests a multipartite mutualism involving fungi exists in this ant-plant and that the role of fungi differs among chamber types.

Intraspecific competition favors ant–plant protective mutualism

AbstractThe dependency of the anti‐herbivore defense on ant–plant protective mutualism often varies depending on abiotic and biotic conditions. Although intraspecific competition is a primary interaction between neighboring plants, its effects on ant–plant mutualisms have yet to be sufficiently elucidated. In order to determine the effects of intraspecific competition and competitor genotype on ant–plant mutualisms, I conducted competition and ant‐removal experiments and examined their effects on damage to the leaves of Urena lobata var. tomentosa plants. I found that larger numbers of worker ants visited the plants growing with non‐siblings than plants growing alone and that plants growing with non‐siblings had a higher shoot to root ratio and secreted greater volumes of extrafloral nectar than plants growing alone and/or with siblings. Under the presence of both sibling and non‐sibling competitors, I observed that when ants were removed from plants, those grown with conspecific neighbors were characterized by a higher percentage of damaged leaf area than plants harboring ants. The effect of ant exclusion on leaf damage was more pronounced in plants grown with non‐siblings than those grown near siblings. However, when the plants were grown alone, I detected no significant difference in percentage leaf damage between the ant‐excluded and ant‐harboring plants. The results indicate that neighboring plants can exert strong effects on ant–plant protective mutualisms, thereby highlighting the need to take into consideration plant–plant interactions in studies on these mutualistic associations.

The dear enemy effect drives conspecific aggressiveness in an Azteca-Cecropia system

Territoriality is costly, and the accurate identification of intruders and the decision to perform aggressive responses are key behavioral traits in social animals. We studied aggression among individuals belonging to close and distant nests of the plant-ant Azteca muelleri, which lives in stems of the pioneer tree Cecropia glaziovii. More specifically, we aim to investigate if the DE (dear-enemy effect—less aggression towards neighbors than strangers) or NN (nasty-neighbor effect—less aggression to strangers than neighbors) effects or even none of them apply for this iconic Azteca-Cecropia system. We further checked if ant aggression towards conspecifics is related to cuticular hydrocarbon profiles (CHCs), which provide chemical cues for nestmate recognition. Therefore, we sampled 46 nests of A. muelleri in three Brazilian Atlantic forest fragments and performed behavioral trials within and between sites. Consistently with the DE effect, we found higher aggression levels in ‘between sites’ versus ‘within sites’ treatments as well as a positive effect of spatial distance on ant aggressiveness. We found no effect of the overall dissimilarities on CHC blend on ant aggressiveness, but of one CHC class, the methylated alkanes. Overall, we provide key insights on nest-mate recognition in obligatory ant-plant mutualisms.

Spatio-temporal variation influences the division of labour in Pseudomyrmex concolor Smith (Formicidae: Pseudomyrmecinae)

Pseudomyrmex concolor is an Amazonian ant that works as an induced biotic defence of its host plant. Nevertheless, there is no information about the division of labour in P. concolor and how it impacts its ant–plant mutualism. We hypothesized that the spatio-temporal variation in P. concolor workers might be reflected in labour division associated with colony/plant defence. For this, we took morphometric measures of ants present on the stem and leaves of Tachigali myrmecophila. They were marked, and the frequency with which they remained in the plant regions and behavioural responses to herbivores presence throughout the day was recorded. The results showed that the spatio-temporal variation influences the division of labour in the P. concolor colony, with workers showing local high fidelity over time and differentiated responses to the same behavioural stimulus, suggesting that the workers perform tasks depending on where they are located in the host plant. Probably workers of P. concolor exhibit age polyethism, with individuals performing different functions in the colony throughout their lifetime and changing their tasks in the colony as they get older and depending on their spatial location.

Streptomyces sp. M54: an actinobacteria associated with a neotropical social wasp with high potential for antibiotic production.

Streptomyces symbionts in insects have shown to be a valuable source of new antibiotics. Here, we report the genome sequence and the potential for antibiotic production of "Streptomyces sp. M54", an Actinobacteria associated with the eusocial wasp, Polybia plebeja. The Streptomyces sp. M54 genome is composed of a chromosome (7.96Mb), and a plasmid (1.91Kb) and harbors 30 biosynthetic gene clusters for secondary metabolites, of which only one third has been previously characterized. Growth inhibition bioassays show that this bacterium produces antimicrobial compounds that are active against Hirsutella citriformis, a natural fungal enemy of its host, and the human pathogens Staphylococcus aureus and Candida albicans. Analyses through TLC-bioautography, LC-MS/MS and NMR allowed the identification of five macrocyclic ionophore antibiotics, with previously reported antibacterial, antitumor and antiviral properties. Phylogenetic analyses placed Streptomyces sp. M54 in a clade of other host-associated strains taxonomically related to Streptomyces griseus. Pangenomic and ANI analyses confirm the identity of one of its closest relatives as Streptomyces sp. LaPpAH-199, a strain isolated from an ant-plant symbiosis in Africa. In summary, our results suggest an insect-microbe association in distant geographic areas and showcase the potential of Streptomyces sp. M54 and related strains for the discovery of novel antibiotics.

The symbiosis between Philidris ants and the ant-plant Dischidia major includes fungal and algal associates

Dischidia major is an epiphyte with pitcher leaves that serve as nests for ants. We investigated this ant-plant symbiosis in two sites in southeastern Thailand, Rayong and Trat, using a morphological and molecular approach. In our study sites, D. major was colonized by one monomorphic ant species of genus Philidris. The inner surface of the pitcher leaves had a black and green lining composed of intermingled coccoid cells and filaments of algae and fungi, reminiscent of a biofilm structure. Microscopic investigation of the algae suggested they belonged to Trebouxia (coccoid cells) and Trentepohliaceae (filaments). Molecular investigation of environmental samples and pure cultures of the fungi revealed five species of Chaetothyriales and four species of Capnodiales, among which two have already been isolated from ant-plant symbioses in Africa and South America and five were described species known from various environments around world. One appears to be an undescribed species. Thus, most fungal associates were likely ubiquitous species. Our study highlights the need to include the identity and functional ecology of microbes in studies of the evolutionary and functional ecology of ant-plant symbioses.

Climate seasonality drives ant–plant–herbivore interactions via plant phenology in an extrafloral nectary‐bearing plant community

Abstract Interactions between ants and plants bearing extrafloral nectaries (EFNs) are among the most common mutualisms in Neotropical regions. Plants secrete extrafloral nectar, a carbohydrate‐rich food that attracts ants, which in return protect plants against herbivores. This ant–plant mutualism is subjected to temporal variation, in which abiotic factors can drive the establishment and frequency of such mutualistic interaction. However, studies investigating how abiotic factors (e.g. climate) directly and indirectly influence ant–plant–herbivore interactions are incipient. In this study, we investigated direct and indirect (via plant phenology) effects of temperature and rainfall on ant–plant–herbivore interactions. To address these goals, each month we estimated six plant phenophases (newly flushed leaves, fully expanded leaves, deciduousness, floral buds, flowers and fruits), the activity of EFNs and abundance of ants and herbivores in 18 EFN‐bearing plant species growing in a markedly seasonal region (the Brazilian Cerrado) during a complete growing season. Our results showed that (a) there were marked seasonal patterns in all plant phenophases, EFN activity and the abundance of ants and herbivores; (b) the peak of EFN activity and ant and herbivore abundance simultaneously occurred at the beginning of the rainy season, when new leaves flushed and (c) rainfall directly and indirectly (via changes in the production of new leaves) influenced EFN activity and this in turn provoked changes in ant abundance (but not on herbivores). Synthesis. Overall, our results build towards a better understanding of how climate drives seasonal patterns in ant–plant–herbivore interactions, explicitly considering plant phenology over time.

Severe fires alter the outcome of the mutualism between ants and a Neotropical savanna tree

AbstractPhysical disturbances, such as fire, may affect the relationship between ants and plants. We evaluated the extent to which severe fires alter the protective effect of ants against the herbivores of an extrafloral-nectary bearing tree. We performed an ant removal experiment and sampled the ant fauna from the same trees over 4 years: the pre-fire year, the fire-year, and again 1 and 2 years later. Ants reduced insect herbivory in the pre-fire year and in the fire-year but failed to provide any plant protection in the two years after fire. The magnitude of the ant effect on herbivory did not differ between the pre-fire year and the fire-year. Fire reduced the abundance of ants with strictly arboreal-nesting habits. However, in the fire year (but not in the subsequent ones), this decline was compensated by an increase in the abundance of arboreal generalists and ground-nesting ants foraging in trees. Our results indicate that severe fires can affect the strength and direction of the ant effects on herbivory by altering the structure of the arboreal ant community and the abundance of insect herbivores. Fire disturbance is thus an important factor of conditionality of ant-plant mutualisms in fire-prone habitats, like the Cerrado savannas.

Oviposition of Minstrellus grandis (Lepidoptera: Riodinidae) in a harmful ant-plant symbiosis

ABSTRACT The oviposition behavior of the rare butterfly Minstrellus grandis (Callaghan, 1999) (Lepidoptera: Riodinidae) is recorded for the first time. Two females laid eggs on the old leaves of an unidentified Triplaris Loefl. ex L. (Polygonaceae), a myrmecophytic plant typically known as ‘Triplaria’ or ‘novice’ tree, inhabited by aggressive ‘taxi’ ants of the genus Pseudomyrmex Lund. 1831 (Hymenoptera: Formicidae). These observations suggest that M. grandis caterpillars live associated with one of the most harmful types of Amazon ant-plant symbiosis.

Contrasting effects of herbivore damage type on extrafloral nectar production and ant attendance

The ant-plant mutualism mediated by extrafloral nectaries (EFNs) is based on the provision of extrafloral nectar (a sugar-rich liquid) in exchange for ant defense against herbivores. The extrafloral nectar production can vary depending on the intensity or types of leaf damage caused by different mouthparts of insect herbivores (i.e., sucking or chewing insects). However, it is poorly known how the type of herbivore damage changes the outcomes of tri-trophic interactions. Here, we address how the damage inflicted by different herbivore groups affects extrafloral nectar production and ants’ attendance and aggressiveness. Through an experimental field study, we tested whether the type of leaf damage, sucking or chewing, changes extrafloral nectar volume and sugar concentration, and subsequently ant composition and behavior. We evaluated the extrafloral nectar production and ant attendance and aggressiveness before and after simulated herbivory in Qualea parviflora (Vochysiaceae), a Brazilian savanna EFN-bearing plant. We found that only plants with sucking damage increased the sugar concentration of their extrafloral nectar, only plants with chewing damage increased ant abundance, and surrogate herbivore predation differed before and after simulated herbivory only for sucking damage. We provided the first evidence that the type of damage can influence ant aggressiveness via changes in extrafloral nectar production, translating to changes in the outcomes of this ant-plant mutualism. Ultimately, studies should consider the effects of herbivore damage type when studying insect-plant interactions.

Optimal Defense Theory in an ant–plant mutualism: Extrafloral nectar as an induced defence is maximized in the most valuable plant structures

Abstract Plants allocate defences in order to decrease costs and maximize benefits against herbivores. The Optimal Defense Theory (ODT) predicts that continuously expressed (i.e. constitutive) defences are expected in structures of high value, whereas defences that are expressed or that increase their expression only after damage or upon risk of damage (i.e. induced defences) are expected in structures of low value. Although there are several studies evaluating ODT predictions, few studies have successfully tested them as a way of measuring ecological investment in extrafloral nectary (EFN)‐mediated ant–plant interactions. Here we compared extrafloral nectar production and ant attractiveness to EFNs located on vegetative versus reproductive plant structures on Qualea multiflora plants subjected to different levels of simulated herbivory. We then addressed the following predictions emerging from the ODT: (a) extrafloral nectar produced in inflorescence EFNs will have higher volumes and calories and will attract more ants than extrafloral nectar produced in leaf EFNs; (b) extrafloral nectar production (volume and calories) and ant attendance will increase after simulated herbivory in leaf EFNs but not in inflorescence EFNs; (c) higher simulated leaf herbivory will induce higher extrafloral nectar production in EFNs on leaves and (d) more attractive extrafloral nectar (higher volume and calories) will attract more ants. Extrafloral nectar volume and calorie content, as well as ant abundance, were higher in EFNs of inflorescences compared to EFNs of leaves both before and after simulated herbivory, consistent with one of our predictions. However, EFNs on both leaves and inflorescences, not on leaves only, were induced by simulated herbivory, a pattern opposite to our prediction. Plants subjected to higher levels of leaf damage produced more and higher calorie extrafloral nectar, but showed similar ant abundance. Finally, more attractive extrafloral nectar attracted more ants. Synthesis. Our results show that extrafloral nectar production before and after simulated herbivory, as well as ant recruitment, varies according to the plant structure on which EFNs are located. Our study is the first to show that ant recruitment via extrafloral nectar follows predictions from Optimal Defense Theory, and that the ant foraging patterns may be shaped by the plant part attacked and the level of damage it receives.

Can Disruption of an Ant–Plant Mutualism Explain a Lack of Recovery of Forest Herbs in Post-Agricultural Forests of New York?

A substantial proportion New York's forests regenerated following agricultural abandonment around the turn of the 20th century. Many myrmecochorous (ant-dispersed) plant species are lacking in these forests decades after land abandonment despite being present in residual stands. To determine if disruption to this ant–plant mutualism can partially explain the current distribution patterns of myrmecochorous plants, we quantified the proportion of seeds removed by ants while accounting for predation by rodents in residual and post-agricultural forests. We experimentally manipulated ant access and controlled for rodent access to seeds of 3 myrmecochorous understory herbs in 3 paired residual and post-agricultural forests in central New York. We identified Aphaenogaster rudis as the primary seed disperser. We found no difference in mean (± 1 SE) proportion of seeds removed by ants between residual stands (73.7% ± 7.7%) and post-agricultural stands (75.8% ± 7.9%). Rodents removed few to no seeds (5.3% ± 1.5%), but an invasive slug, Arion subfuscus (Dusky Arion), was observed removing elaiosomes from seeds in both stand types. Our data indicated neither a lack of ant-dispersal activity nor excessive rodent predation would be limiting to dispersal of myrmecochorous seeds in post-agricultural forests during the period of our study. Given the presence of A. rudis in post-agricultural stands, programs to assist plant migration will likely be sufficient to reestablish this ant–plant mutualism in degraded sites.

Ants suppressing plant pathogens: a review

Ant–plant mutualisms are usually regarded as driven by ants defending plants against herbivores in return for plant‐produced food rewards and housing. However, ants may provide additional services. In a review of published studies on ant–pathogen–plant interactions, we investigated whether ants’ extensive hygiene measures, including the use of ant‐produced antibiotics, extend to their host plants and reduce plant pathogen loads. From 30 reported species combinations, we found that the presence of ants lead to reduced pathogen levels in 18 combinations and to increased levels in 6. On average, ants significantly reduced pathogen incidence with 59%. This effect size did not differ significantly from effect sizes reported from meta‐analyses on herbivore protection. Thus, pathogen and herbivore protection could be of equal importance in ant–plant mutualisms. Considering the abundance of these interactions, ecological impacts are potentially high. Furthermore, awareness of this service may stimulate the development of new measures to control plant diseases in agriculture. It should be noted, though, that studies were biased toward tropical ant–plant symbioses and that the literature in the field is limited at present. Future research on plant pathogens is needed to enhance our understanding of ant–plant mutualisms and their evolution.

Plant killing by Neotropical acacia ants: ecology, decision‐making, and head morphology

AbstractMutualistic species often associate with several partners that vary in the benefits provided. In some protective ant–plant mutualisms, ants vary in the extent at which they kill neighboring vegetation. Particularly, in acacia ants (Pseudomyrmex), the area around the host tree that ants keep free from vegetation (“clearings”) vary depending on the species. This study assessed whether interspecific variation in clearing size corresponds to workers biting on plant tissue of different thickness. As expected, workers from species making the largest clearings bit more often on thicker plant tissues than workers from species making smaller clearings. Because head shape affects mandible force, I also assessed whether pruning on thick tissue in mutualistic ant species or being a predator in non‐mutualistic species correlated with broader heads, which yield stronger mandible force. The species with the broader heads were non‐mutualistic predators or mutualistic pruners of thick tissues, which suggest that pruning neighboring vegetation in non‐predatory species demands force even when the ants do not kill prey with their mandibles. The findings reveal that clearing size variation in mutualistic ant partners of plants can also be observed at the level of individual decision‐making processes among workers, and suggest that head morphology could be a trait under selection in protective ant–plant mutualisms.Abstract in Spanish is available with online material.

The resource‐mediated modular structure of a non‐symbiotic ant–plant mutualism

1. Plant–animal mutualisms are key processes that influence community structure, dynamics, and function. They reflect several neutral and niche‐based mechanisms related to plant–animal interactions.2. However, the strength with which these processes influence community structure depends on functional traits that influence the interactions between mutualistic partners. In mutualisms involving plants and ants, nectar is the most common reward, and traits such as quantity and quality can affect ant species' responses by influencing their recruitment rates and aggressiveness.3. In this study, nectar traits that mediate ant–plant defensive mutualisms were manipulated to test whether resource quantity and quality affect the structure of ant–plant interaction networks. A downscaling approach was used to investigate the interaction network between ant species and individual plants of the extrafloral nectary‐bearing terrestrial orchid Epidendrum secundum.4. We found a short‐term reorganization of the ant assemblage that caused the interaction networks to become more specialised and modular in response to a more rewarding nectar gradient. Furthermore, the ant species tended to narrow their foraging range by limiting their associations to one or a few individual plants.5. This study shows that ant species' responses to variable resource traits play an important role in the structure of the ant–plant interaction network. We suggest that more rewarding nectar enhanced aggressiveness and a massive recruitment of some ant species, leading to lower niche overlap and thus a less connected and more specialised network.

Extrafloral nectaries mediate the arboreal beetle community (Coleoptera) in a Neotropical rainforest

ABSTRACTNectaries are structures that secrete a sugary solution and can occur on vegetative and/or reproductive parts of plants. The significance of floral nectaries to reward vertebrate and arthropod pollinators is well supported. The role of extrafloral nectaries (EFNs) is more ambiguous, though research has been skewed to the ant-plant mutualism. Many other insects feed at EFNs, but these interactions are vastly understudied. This study addresses the hypothesis that EFNs may influence the occurrence and structure of Neotropical canopy beetle communities. Seven canopy trees (four families) exhibiting EFNs and their associated beetles were studied over a one-year period in southern Venezuela. In total, 6818 adult beetles identified to 868 species were recorded on 25 investigated canopy tree species (#47 individuals). Of the 868 beetle species, 150 species (517 individuals; 17.3% species) from 20 families were observed drinking from foliar EFNs on seven EFN-bearing tree species. Dietary dependence on EF nectar varied, with 95 beetle species utilising this nectar within a broader diet and 55 species found feeding exclusively on EFNs. This study demonstrates unequivocally that EF nectar is a frequently utilised food resource of many beetle adults and beetles have been a significantly underestimated visitor group. A more detailed study was conducted on six individual canopy trees of two species of Chrysobalanaceae, Licania hebantha Mart. ex Hook. f. and Moquilea subarachnophylla (Cuatrec.) Sothers and Prance. In total, 115 individual adults of 64 beetle species were collected on nectar secreted on newly-sprouted leaves. These beetle assemblages were dominated by species utilising EF nectar and were associated with distinct phenological phases of the host trees. Altogether, the beetle survey found support for the hypothesis that EFNs influence the occurrence and structure of beetle communities. These beetle-EFN relationships have implications for spatial arrangement, community assembly and evolution of both host plants and beetles. Like ant-EFN mutualism, EFN-bearing trees and beetles may also form mutualism. It is possible that the plants offer easier access to a nutritious resource that may deflect herbivory of vegetative parts.

Left out in the cold: temperature-dependence of defense in an African ant-plant mutualism.

Many tropical plants are defended by ants, and the costs and benefits of these mutualisms can vary across gradients of herbivory, soil fertility, latitude, and other environmental factors. Yet despite an abundant literature documenting thermal constraints on ant activity and behavior, we know little about whether temperature variation can influence the benefits conferred by ants to plants. We evaluated the effects of dawn-to-dusk fluctuations in temperature on patrolling and aggressive behavior in four arboreal ant mutualists of Acacia drepanolobium trees in central Kenya. We found that ant aggressive behavior significantly increased with branch surface temperature, primarily in the two most aggressive ant species: Crematogaster mimosae and C.nigriceps workers attacked a simulated herbivore at higher rates as surface temperature rose. In a browsing experiment, we found that goats browsed more frequently and for longer durations on C.mimosae-defended trees during cooler times of day, while goat browsing on plants from which ants had been removed was not affected by temperature. Our study demonstrates temperature-dependence in the efficacy of ant defense against herbivory and suggests that these ant-plants may be more vulnerable to herbivory during cooler hours of the day, when many native browsers are most active.

The ecological and evolutionary importance of nectar‐secreting galls

AbstractSome species of cynipid wasp engage in mutualisms with ants by producing nectar‐secreting galls, providing carbohydrates, and receiving protection from parasitoids. The galls are functionally similar to extrafloral nectaries, plant structures well known for their role in ant–plant mutualisms. Though not well known, nectar‐secreting galls may have important ecological and evolutionary implications for arthropods, plants, and the evolution of ant‐mutualisms. Here, I review the known ecology of nectar‐secreting galls and speculate on their wider ecological significance based on past research and similar ecological systems. I then develop a conceptual framework for considering the possible historical role of nectar‐secreting galls in the evolution of ant‐mutualisms. I review current knowledge on the origin of ant‐mutualisms and develop a hypothesis for the role of nectar‐secreting galls using examples of similar, contemporary species interactions. Finally, I lay out some of the future directions for research into nectar‐secreting galls and their species interactions, including important questions that remain to be addressed. Future studies of the diversity and ecology of nectar‐secreting galls are necessary to determine the extent to which they may be involved in ecological functioning and the evolution of ant‐mutualisms, and it is hoped that this review will contribute to motivating and developing future research.