Myrmecophytic Species Research Articles

Phylogeny and the evolutionary origins of myrmecophytism in the Neonauclea clade (Rubiaceae) revisited, with particular emphasis on the Philippine lineages

The Australasian Neonauclea is the largest genus of the tribe Naucleeae (subfamily Cinchonoideae, Rubiaceae) and is well known for its extensive radiation of myrmecophytic species. The genus is paraphyletic with respect to the genera Ludekia and Myrmeconauclea, and these three genera constitute the Neonauclea clade sensu Lofstrand et al. The Philippines is a center of species diversity of Neonauclea; however, its members have yet to be included in any molecular studies. We produced a phylogeny of the Neonauclea clade based on sequence data from nuclear (ETS and ITS) and plastid (rbcL and trnT-F) markers and including a large sampling of Neonauclea species from the Philippines. The resulting phylogeny was used to assess the phylogenetic positions and relationships of the Philippine Neonauclea species within the Neonauclea clade. We also reassessed the origins of myrmecophytism in the Neonauclea clade using ancestral state reconstructions. The sampled Philippine Neonauclea were resolved in five morphologically and geographically distinct clades. Our ancestral state reconstructions inferred a non-myrmecophytic ancestor for the Neonauclea clade, as shown by Razafimandimbison et al., and suggested at least two independent origins of myrmecophytism, one in myrmecophytic Myrmeconauclea and another in the myrmecophytic Neonauclea species from core Neonauclea. Losses of myrmedomes through multiple evolutionary reversals back to the non-myrmedome condition were inferred within core Neonauclea. Unlike the Bornean myrmecophytic lineages, our results favored a single origin of the Philippine endemic myrmecophytic Neonauclea.

Host‐plant dissections reveal contrasting distributions of Crematogaster ants and their symbionts in two myrmecophytic Macaranga species

1. Ant–plant mutualisms are among the most widespread and ecologically important insect–plant interactions in the tropics. The multitrophic mutualism involving Macaranga plants (Euphorbiaceae) and Crematogaster ants (Formicidae) is the most diverse in Southeast Asia. This interaction also includes trophobiotic scale insects (Coccidae) and nematodes inhabiting ant refuse piles.2. Here two myrmecophytic systems were compared, Macaranga trachyphylla with Crematogaster captiosa (Mt + Cc) and Macaranga beccariana with Crematogaster decamera (Mb + Cd), using a fine‐scale dissection of the stems. For the two plant species, for each internode, both contents (ants, coccids, refuse piles) and structure (internode height, numbers of open and occluded ant holes) were recorded.3. There were significant patterns in the vertical distribution of ant colonies and their symbionts in the plant stems. Most coccids were kept in the highest sections of both systems, although Mb + Cd hosted a broader range of coccid species than Mt + Cc. Three nematode species were recorded, but with a rather low specificity to plant or ant species. Furthermore, the fine‐scale distribution showed aggregation of closed holes with ant brood and separation of nematode‐infested refuse piles from eggs.4. The results of this study indicate that ants manipulate spatial colony structure via distribution of brood, holes and the symbionts. It is suggested that ants optimise the location of refuse piles and occluded holes via spatial heterogeneity in their distribution among internodes. This paper discusses the protective role of occluded holes and demonstrates some general interactions with other symbiotic fauna.

Species Richness and Habitat Suitability of Myrmecophytes in Bengkulu : Host Tree, Coexist Epiphytes and Animals

Myrmecophytes or locally known as simbagh utak are common medicinal plants used by locals in Bengkulu, especially in South Bengkulu, for treating various diseases. Despite their potential as medicines, there is no report on biotic factors can be used to indicate of Myrmecophytes species’ richness and habitat suitability. The objectives of this research were to analyze the Myrmecophytes’ species richness and habitat suitability. This study used the purposive sampling method by exploring the area where Myrmecophytes were commonly found. The biotic factors of Myrmecophytes were analyzed by identifying the tree host, the other epiphyte plant grew around them, and animal occupants on the tuber of the Myrmecophytes. The Myrmecophytes distribution was analyzed by using ArcGIS10.1. The results showed that there were two species of Myrmecophytes, namely Hydnophytum formicarum and Myrmecodia tuberosa in the study area. The Myrmecophytes attached and hung in 9 species of host trees. The characteristics of host trees are high trees with large diameter, mostly rough-barked; some were cracked and mossy. The highest frequency of host trees included Hevea brasiliensis and Durio zibethinus. Myrmecophytes coexisted with 12 species of epiphytes. Epiphyte plants like Dendrobium sp. and Drymoglossum piloselloides can be used to indicate the presence of Myrmecophytes. Ants made up the most predominantly animal found living inside the tubers of Myrmecophytes, with some cockroaches and termites found at the tuber of Hydnophytum. Information on species' richness and habitat suitability of Myrmecophytes can serve as supporting data for conservation efforts in Bengkulu to prevent the extinction of this species.

Diversity and Distribution of Myrmecophytes in Bengkulu Province

<p>Myrmecophyte is a common medicinal plant used by local people in Indonesia for treating various diseases especially in Papua. Bengkulu province is one of the myrmecophyte habitats, but there has no report on its identity and distribution. The objectives of this research were to identify the diversity and analyze the myrmecophytes distribution as well as factor affecting its presence. This study used purposive sampling method by exploring the area where myrmecophytes commonly found. The myrmecophyte distribution was analyzed using <em>Morishita</em> index and <em>Arcgis</em> 10.1, and the autecological analysis of abiotic factors was performed using <em>Principal Component Analysis</em> (PCA) generated from Minitab 16. The results of this research showed that there were two species of myrmecophytes in Bengkulu province, namely <em>Hydnophytum formicarum</em> and <em>Myrmecodia tuberosa</em>, as well as two variants of <em>M. tuberosa</em> i.e. <em>M. tuberosa</em> 'armata’ and <em>M. tuberosa</em> 'siberutensis'. The distribution of myrmecophytes was mostly randomly scattered in Central Bengkulu regency, Seluma, North Bengkulu, South Bengkulu, and Kaur. Their distributions were affected by light intensity and temperature. The data of this research can be used as basic information for carried out conservation efforts in Bengkulu province. The abundance of myrmecophytes is also used as a source of additional income for local people in Bengkulu province. </p>

Neonauclea viridiflora (Rubiaceae), a New Species of Naucleeae from Eastern Samar, with Notes on Myrmecophytic Species in the Philippines

Abstract A new myrmecophytic species, Neonauclea viridiflora, is described from Eastern Samar, Philippines. It bears similarity to N. formicaria, but is easily distinguished by having obovate leaves, smaller flowering heads of 30–35 mm, persistent calyces that are glabrous inside the tube, calyx shafts that are connate at the bases for 0.8–2.5mmor sometimes entirely connate with the adjacent lobe, apical portions of the calyces that are bluntly turbinate but globose to clavate when dry, calyx summits that are bluntly conical but the apex is somewhat flattened when dry, and smaller and slender light green corollas. Comparative illustrations of the calyx lobes, a key to the Philippine myrmecophytic Neonauclea species, and a map for these species' distributions in the Philippines are provided in the study.

Neonauclea connicalycina: a new myrmecophytic species of Naucleeae (Rubiaceae) from Cebu, Philippines

The new myrmecophytic species, Neonauclea connicalycina, from Carmen, Cebu, Philippines closely resembles N. formicaria, which also occurs in Philippines, but differs from that by its smaller mature flowering heads, fusiform apical portions of the calyces, longer and sharply pyramidal calyx summits that are pallid brown when dry, calyx lobes that are connate for 1–2 mm and fall off together in a unit, and smaller, more slender corollas. Description, illustration and ecological comments about the new species are provided.

Reduced ant defenses in Macaranga myrmecophytes (Euphorbiaceae) infested with a winged phasmid Orthomeria cuprinus

AbstractMacaranga is a tree genus that includes many species of myrmecophytes, which are plants that harbor ant colonies within hollow structures known as domatia. The symbiotic ants (plant–ants) protect their host plants against herbivores; this defense mechanism is called ‘ant defense’. A Bornean phasmid species Orthomeriacuprinus feeds on two myrmecophytic Macaranga species, Macaranga beccariana and Macaranga hypoleuca, which are obligately associated with Crematogaster ant species. The phasmids elude the ant defense using specialized behavior. However, the mechanisms used by the phasmid to overcome ant defenses have been insufficiently elucidated. We hypothesized that O.cuprinus only feeds on individual plants with weakened ant defenses. To test the hypothesis, we compared the ant defense intensity in phasmid‐infested and non‐infested M. beccariana trees. The number of plant–ants on the plant surface, the ratio of plant–ant biomass to tree biomass, and the aggressiveness of plant–ants towards experimentally introduced herbivores were significantly lower on the phasmid‐infested trees than on the non‐infested trees. The phasmid nymphs experimentally introduced into non‐infested trees, compared with those experimentally introduced into phasmid‐infested trees, were more active on the plant surface, avoiding the plant–ants. These results support the hypothesis and suggest that ant defenses on non‐infested trees effectively prevent the phasmids from remaining on the plants. Thus, we suggest that O.cuprinus feeds only on the individual M. beccariana trees having decreased ant defenses, although the factors that reduce the intensity of the ant defenses remain unclear.

COMPLEXES OF MYRMECOPHYTES DISTRIBUTED BY ANTS FORMICA RUFA AND F. POLYCTENA IN THE UKRAINIAN CARPATHIANS

Study of myrmecochory in the forests of the Ukrainian Carpathians in fact has not been carries out. Only several publications have been dedicated to the problems of myrmecochory in the forests of Ukraine. Taking this into account and a great number of myrmecophytes in coniferous, deciduous and mixed forests of the temperate zone, the aim of the work was to identify myrmecophytes which are connected with Formica rufa and F. polyctena, in different types of forests on the territory of the Ukrainian Carpathians.The observation was carried out during the field season of 2009-2011 in the vicinity of ant hills of two types of insects on the territories of the coniferous forest of Vorokhtianskoie forestry, mixed forest of Nadvirnianskoie forestry and deciduous forest of Beregivske forestry.In the three studied types of the forest 53 species of myrmeciphytes, which belong to 30 families, 26 orders and 5 classes, were identified. The largest number of myrmecophytes belong to orders Rosales and Lamiales (respectively 19.6 and 13.5 %).No sharp change in the number of myrmecophytes was observed in the coniferous and deciduous forests in representatives of F. polyctena and F. rufa, with only 2 species of myrmecophytes: European dewberry (Rubus caesius) and ground elder (Aegopodium podagraria) being found in the mixed forest. Aegopodium podagraria and Rubus caesius are universal myrmecophytes for ants on the studied territories, independently on the type of forest.In the coniferous forest 24 species of myrmecophytes are connected with F. rufa, 26 – with F. polyctena – ; in deciduous – 13 and 16 respectively; and in the mixed on – 2 and 16 species.

How Do Scale Insects Settle into the Nests of Plant-Ants on Macaranga Myrmecophytes? Dispersal by Wind and Selection by Plant-Ants

This report elucidates the process of settlement by Coccus scale insects into Crematogaster plant-ant nests formed inside the hollow stems of a myrmecophytic species, Macaranga bancana, in a tropical rain forest. We collected wafting scale insect nymphs from the canopy using sticky traps and characterized the DNA sequence of the trapped nymphs. In addition, we experimentally introduced first-instar nymphs of both symbiotic and nonsymbiotic scale insects to M. bancana seedlings with newly formed plant-ant colonies. Nymphs of symbiotic species were generally carried by ants into their nests within a few minutes of introduction. Most nymphs of nonsymbiotic species were thrown to the ground by ants. Our results suggest that in Crematogaster–Macaranga myrmecophytism, symbiotic coccids disperse by wind onto host plant seedlings at the nymphal stage, and plant-ants actively carry the nymphs landing on seedlings into their nests in discrimination from nonsymbiotic scale insects.

English

Castor bean (Ricinus communis L.) is a myrmecophytic plant species with specialized extrafloral nectar (EFN) glands that serve to attract predatory insects, which in return defend plant-tissues against herbivores. The EFN glands on castor bean plants are located along the leaf petioles as well as on the peduncles of its imperfect (unisexual) flowers. This field-project evaluates the richness, diversity, and species assemblage of insects visiting EFN glands located on (female and male) flower peduncles and leaf petioles on castor bean plants growing in a Southern California coastal landscape. We detected that EFN glands on female-flower peduncles were visited by an insect community that was distinct from that of the other two EFN gland types on castor bean. Additionally, the insects visiting EFN glands on male-flower peduncles more closely resembled those observed visiting EFN glands on leaf petioles. We conclude that the observed differences in the biotic defense of foliar and unisexual floral tissues on castor bean are congruent with the optimal plant-defense strategy of a monoecious pioneer species. Key words: Ant-plant interactions, monoecious, mutualism, myrmecophyte, plant-defense optimality, sexual dimorphism.

Host-plant use by twoOrthomeria(Phasmida: Aschiphasmatini) species feeding onMacarangamyrmecophytes

Myrmecophytes depend on symbiotic ants (plant-ants) to defend against herbivores. Although these defensive mechanisms are highly effective, some herbivorous insects can use myrmecophytes as their host-plants. The feeding habits of these phytophages on myrmecophytes and the impacts of the plant-ants on their feeding behavior have been poorly studied. We examined two phasmid species, Orthomeria alexis and O. cuprinus, which are known to feed on Macaranga (Euphorbiaceae) myrmecophytes in a Bornean primary forest. Our observations revealed that: (i) each phasmid species relied on two closely-related myrmecophytic Macaranga species for its host-plants in spite of their normal plant-ant symbioses; and (ii) there was little overlap between their host-plant preferences. More O. cuprinus adults and nymphs were found on new leaves, which were attended by more plant-ants than mature leaves, while most adults and nymphs of O. alexis tended to avoid new leaves. In a feeding choice experiment under ant-excluded conditions, O. alexis adults chose a non-host Macaranga myrmecophyte that was more intensively defended by plant-ants and was more palatable than their usual host-plants almost as frequently as their usual host-plant, suggesting that the host-plant range of O. alexis was restricted by the presence of plant-ants on non-host-plants. Phasmid behavior that appeared to minimize plant-ant attacks is described.

Exploitation of Food Bodies onMacarangaMyrmecophytes by Larvae of a Lycaenid Species,Arhopala zylda(Lycaeninae)

ABSTRACT. Larvae of Arhopala zylda (Lycaenidae) feed on food bodies (FBs) produced by two Macaranga (Euphorbiaceae) myrmecophytic species, M. beccariana and M. hypoleuca. We examined their feeding behavior in detail via field observations and rearing experiments in the field and laboratory. Larvae of A. zylda fed only on FBs and not leaves during the first through third instars; during the fourth (final) instar, they ate both FBs and leaves of the host plants. The larvae actively fed on FBs on young leaves, which were always attended by many plant symbiotic ants. These results suggested that A. zylda larvae depend entirely on FBs for food, except late in the final instar, and that the FB-feeding habit is associated with special traits that enable the larvae to evade ant aggression, which usually functions as an effective anti-herbivore defense for the host plants.

The ontogeny of plant indirect defenses

Abstract Plants frequently attract natural enemies of their herbivores, resulting in a reduction in tissue damage and often in enhanced plant fitness. While such indirect defenses can dramatically change as plants develop, only recently have ecologists begun to explore such changes and evaluate their role in mediating plant–herbivore–natural enemy interactions. Here we review the literature documenting ontogenetic patterns in plant rewards (i.e. extrafloral nectaries (EFNs), food bodies (FBs) and domatia) and volatile organic compounds (VOCs), and identify links between ontogenetic patterns in such traits and the attraction of natural enemies (ants). In the case of reward traits we concentrate in ant–plant studies, which are the most numerous. We report that all indirect defensive traits commonly vary with plant age but ontogenetic trajectories differ among them. Myrmecophytic species, which provide both food and shelter to their defenders, do not produce rewarding traits until a minimum size is reached. Then, a pronounced increase in the abundance of food rewards and domatia often occurs as plants develop, which explains the temporal succession or colony size increase of mutualistic ant species and, in some cases, leads to a reduction in herbivore damage and enhanced fitness as plants age. In contrast, ontogenetic patterns were less consistent in plant species that rely on VOC emissions to attract natural enemies or those that provide only food rewards (EFNs) but not nesting sites to their associated ants, showing an overall decline or lack of trend with plant development, respectively. Future research should focus on uncovering: (i) the costs and mechanisms underlying ontogenetic variation in indirect defenses, (ii) the relative importance of environmental and genetic components shaping these ontogenetic trajectories, and (iii) the consequences of these ontogenetic trajectories on plant fitness. Advances in this area will shed light on the context dependency of bottom-up and top-down controls of herbivore populations and on how natural selection actually shapes the ontogenetic trajectories of these traits.

Production of food bodies on the reproductive organs of myrmecophytic Macaranga species (Euphorbiaceae): effects on interactions with herbivores and pollinators

AbstractIn protective ant–plant mutualisms, plants offer ants food (such as extrafloral nectar and/or food bodies) and ants protect plants from herbivores. However, ants often negatively affect plant reproduction by deterring pollinators. The aggressive protection that mutualistic ants provide to some myrmecophytes may enhance this negative effect in comparison to plant species that are facultatively protected by ants. Because little is known about the processes by which myrmecophytes are pollinated in the presence of ant guards, we examined ant interactions with herbivores and pollinators on plant reproductive organs. We examined eight myrmecophytic and three nonmyrmecophytic Macaranga species in Borneo. Most of the species studied are pollinated by thrips breeding in the inflorescences. Seven of eight myrmecophytic species produced food bodies on young inflorescences and/or immature fruits. Food body production was associated with increased ant abundance on inflorescences of the three species observed. The exclusion of ants from inflorescences of one species without food rewards resulted in increased herbivory damage. In contrast, ant exclusion had no effect on the number of pollinator thrips. The absence of thrips pollinator deterrence by ants may be due to the presence of protective bracteoles that limit ants, but not pollinators, from accessing flowers. This unique mechanism may account for simultaneous thrips pollination and ant defense of inflorescences.

Change in biomass of symbiotic ants throughout the ontogeny of a myrmecophyte, Macaranga beccariana (Euphorbiaceae)

Macaranga myrmecophytes (ant-plants) provide their partner symbiotic ants (plant-ants) with food bodies as their main food, and they are protected by the plant-ants from herbivores. The amount of resource allocated to food bodies determines the plant-ant colony size and consequently determines the intensity of ant defense (anti-herbivore defense by plant-ants). As constraints in resource allocation change as plants grow, the plant-ant colony size is hypothesized to change with the ontogenesis of Macaranga myrmecophyte. To determine the ontogenetic change in the relative size of the plant-ant colony, we measured the dry weights of the whole plant-ant colony and all of the aboveground parts of trees at various ontogenetic stages for a myrmecophytic species (Macaranga beccariana) in a Bornean lowland tropical rain forest. Ant biomass increased as plant biomass increased. However, the rate of increase gradually declined, and the ant biomass appeared to reach a ceiling once trees began to branch. The ant/plant biomass ratio consistently decreased as plant biomass increased, with the rate of decrease gradually accelerating. We infer that the ontogenetic reduction in ant/plant biomass ratio is caused by an ontogenetic change in resource allocation to food rewards for ants related to the physiological changes accompanying the beginning of branching.

Parenchyma: a neglected plant tissue in the Cecropia/ant mutualism

The Cecropia/Azteca association is a well studied and perhaps the best known mutualistic system in the Neotropics. In this study we assessed the ultrastructure of the parenchymal tissue of the septum inside the internodes of two Cecropia species, Cecropia obtusifolia (a myrmecophytic species) and C. angustifolia (a non-myrmecophytic species), through the use of scanning electron microscopy. We found a series of large oval cavities in the parenchyma of C. obtusifolia, which were absent in the parenchyma of C. angustifolia, and which seemed to be spatially associated with vascular bundles. We also found two layers of fibers in C. obtusifolia, one on each side of the septum. Finally, the parenchymal cells of C. angustifolia were filled with several tiny oval bodies, which appeared to be plastids (perhaps serving as storage) and which were completely absent in C. obtusifolia. The structural differences between these two Cecropia species, as well as other evidence from the behavior of the ants, suggests that the parenchyma of myrmecophytic Cecropia species provides an additional source of nutrition for the Azteca queens during colonization of Cecropia saplings. Other possible uses of parenchymal tissue by the ant colony are also discussed.

Effects of symbiotic coccid on the plant-ant colony growth in the myrmecophyte Macaranga bancana

Macaranga (Euphorbiaceae) myrmecophytes provide their partner ants (plant-ants) with hollow stems used as nesting spaces, as well as food bodies as food rewards. In return, they benefit from the anti-herbivore defense of the ants. The plants harbor not only ants but also specific honeydew-producing coccids, which live inside the ant nests in the hollow stems. Although the honeydews are fed by the plant-ants, their effect on the growth of plant-ant colonies is undetermined. In this study, we investigated how such myrmecophilous coccids, Coccus spp. affect the colony growth of plant-ants, Crematogaster spp. on the myrmecophytic species M. bancana. We compared the growth of plant-ant colonies on seedlings from which coccids were experimentally excluded with that on seedlings into which specific myrmecophilous coccids were experimentally introduced. Foundress queens in 14 of 16 coccid-excluded seedlings died by the time we dissected the seedlings 235-637 days after the seedlings were transplanted in a meshed nursery. In contrast, those on 12 of 17 coccid-introduced seedlings survived during that period, with the survival rate of queens differing significantly between treatments. This result suggests that the symbiotic coccids provide nutrients that facilitate the colony growth of plant-ants inhabiting Macaranga myrmecophytes.

Volatiles of myrmecophytic Piper plants signal stem tissue damage to inhabiting Pheidole ant‐partners

Summary The major aim of this paper was to explore the mechanistic basis of induced defensive ant response in myrmecophytic Piper species and their ant‐partner Pheidole bicornis by combining experimental trials and chemical analysis. In field experiments, the response of Pheidole ants to simulated stem‐damage of their host plant was documented. Their reaction to other myrmecophytic and non‐myrmecophytic Piper species was explored by fixing respective stem sections onto inhabited Piper fimbriulatum individuals. After artificial damage to stems of P. fimbriulatum and stem sections from other myrmecophytic Piper, the number of ants increased to a maximum of 63 individuals on the damaged internode within the first 10 min. By contrast, no or only a poor reaction was elicited by stem sections from the selected non‐myrmecophytic Piper species. Solid‐phase microextraction/gas chromatography–mass spectrometry identified 68 volatile organic compounds (VOCs) which were emitted from wounded stem bark of three myrmecophytic (P. fimbriulatum, P. obliquum, P. sagittifolium) and two non‐myrmecophytic (P. hispidum, P. riparense) Piper species, comprising monoterpenes, sesquiterpenes, simple aromatic compounds, and green leaf volatiles (GLVs, oxylipins). Despite considerable variation in the VOC profiles, an analysis of similarities (anosim) classified the accumulation of the sesquiterpenes β‐caryophyllene, germacrene D and emission of the oxylipin reactive electrophilic species (RES) compounds hexanal, cis‐3‐hexene‐1‐ol, 2‐hexenal, 2‐undecanone and 1‐hexanol as characteristic of the myrmecophytic species. Synthesis. Field experiments showed that mechanical disturbance of myrmecophytic Piper stems is not sufficient to elicit recruitment and alertness of the ant‐partner Ph. bicornis, but that specific volatiles released from the host plant are responsible. Analyses of the VOCs identified after simulated stem damage of three myrmecophytic and two non‐myrmecophytic Piper species revealed differences in their VOC emission profiles: Only in the myrmecophytic species were induced stress compounds found, such as various oxylipin RES or the sesquiterpene β‐caryophyllene, which are typically emitted after plant damage for interplant signalling. Some of these compounds (e.g. hexanal, 1‐hexanol) are known to induce alerting and alarm behaviours in several ant species. Our study provides evidence that the VOCs of the Piper host plant may signal stem damage and induce recruitment and alert behaviour of associated Pheidole ants.

A new quantitative classification of ecological types in the bromeliad genus Tillandsia (Bromeliaceae) based on trichomes

Using collection specimens, we measured the density and wing area of trichomes in 37 species of the bromeliad genus Tillandsia, specifically the abaxial proximal, abaxial distal, adaxial proximal and adaxial distal parts of the leaf. The product of the trichome "wing" area by the number of trichomes (means) produced a pure number (T) that was correlated to ecological features. The correlation was positive with respect to arid environments (xeric Tillands) and negative with respect to humid environments (mesic Tillands). Bulbous, and particularly myrmecophytic species and species with tanks, represented particular categories. Other intermediate types were identified based on the T number, totalling five ecological types. In comparison with other systems of ecological typification for Tillands and other Bromeliaceae, the present system offers measurable data whose analysis is reproducible.

The fitness consequences of bearing domatia and having the right ant partner: experiments with protective and non-protective ants in a semi-myrmecophyte

The fitness advantage provided by caulinary domatia to myrmecophytes has never been directly demonstrated because most myrmecophytic species do not present any individual variation in the presence of domatia and the removal of domatia from entire plants is a destructive process. The semi-myrmecophytic tree, Humboldtia brunonis (Fabaceae: Caesalpinioideae), is an ideal species to investigate the selective advantage conferred by domatia because within the same population, some plants are devoid of domatia while others bear them. Several ant species patrol the plant for extra-floral nectar. Fruit production was found to be enhanced in domatia-bearing trees compared to trees devoid of domatia independent of the ant associate. However, this domatium effect was most conspicuous for trees associated with the populous and nomadic ant, Technomyrmex albipes. This species is a frequent associate of H. brunonis, inhabiting its domatia or building carton nests on it. Ant exclusion experiments revealed that T. albipes was the only ant to provide efficient anti-herbivore protection to the leaves of its host tree. Measures of ant activity as well as experiments using caterpillars revealed that the higher efficiency of T. albipes was due to its greater patrolling density and consequent shorter lag time in attacking the larvae. T. albipes also provided efficient anti-herbivore protection to flowers since fruit initiation was greater on ant-patrolled inflorescences than on those from which ants were excluded. We therefore demonstrated that caulinary domatia provide a selective advantage to their host-plant and that biotic defence is potentially the main fitness benefit mediated by domatia. However, it is not the sole advantage. The general positive effect of domatia on fruit set in this ant-plant could reflect other benefits conferred by domatia-inhabitants, which are not restricted to ants in this myrmecophyte, but comprise a large diversity of other invertebrates. Our results indicate that mutualisms enhance the evolution of myrmecophytism.