Myrmecochorous Plants Research Articles

Ant removal distance, but not seed manipulation and deposition site increases the establishment of a myrmecochorous plant.

Myrmecochory (seed dispersal by ants) is a unique seed dispersal syndrome among invertebrates. It comprises three main phases: seed removal, seed manipulation, and seed deposition. However, the contribution of each phase to seed and seedling fate remains unclear. Here, we experimentally quantified the effects of each phase of myrmecochory on seed germination and seedling establishment, the two most critical life history stages involved in plant recruitment. We established 30 sample points, and each included an adult Mabea fistulifera tree, an Atta sexdens nest entrance, and six seed depots. We monitored the germination of M. fistulifera seeds for 3months and subsequently followed the growth and mortality of the resulting seedlings for 12months. Only the dispersal distance influenced plant establishment, reducing seed germination and increasing seedling growth, but with no effect of seed manipulation and deposition site. Despite the contrasting effects of distance on seed germination and seedling growth, the positive effect of dispersal distance on seedling growth was ten times greater than the negative effect on seed germination. Moreover, A. sexdens behaved neither as granivore nor as herbivore of M. fistulifera seeds or seedlings, which suggests that seed dispersal by A. sexdens is advantageous to M. fistulifera. Thus, the joint occurrence of these two species in disturbed areas could have a positive effect on this pioneer plant population, which might promote forest regeneration.

Invasive ants disperse seeds farther than native ants, affecting the spatial pattern of seedling recruitment and survival

Mutualists can vary in the quantity and quality of service which they provide to their partners. Variation in seed disperser quality depends on seed-processing traits, dispersal distance, and deposition location, all of which ultimately affect plant fitness. Here, we compared these aspects of seed dispersal quality between a native and an invasive ant species, and examined how they affect competition and plant performance. Using experimental mesocosm communities, we examined how these two ant species affect the spatial pattern of recruitment and establishment for four myrmecochorous plant species, including one invasive species. We measured the locations of dispersed seedlings relative to ant nests, adult plants, and other dispersed seedlings, as well as measured the effects of location on plant performance. The invasive ant, Myrmica rubra, secondarily dispersed seeds farther from its nests, creating a less clumped pattern of seedling recruitment compared to the native ant, Aphaenogaster rudis. Plant species responded differently to dispersal. Invasive seedlings recruited farther from adult plants than native seedlings, and had higher survival the farther they were from conspecifics. In contrast, native plants had higher survival and grew taller when dispersed farther from invasive plants. We show that seed-dispersing ant partners differ in mutualist quality creating differences in dispersal distance and deposition location that affects a plant's competitive environment. Our results reveal the potential for long-term consequences on plant community structure with changing ant partner identity. We emphasize the need to examine dispersal quality in addition to quantity to uncover the importance of partner identity in structuring communities.

Effect of neighboring seeds associated with habitats on the seed removal of two coexisting myrmecochorous plants in central China

Although neighboring plants can influence animal-seed dispersal interactions, little is known about the effect of neighboring seeds and the influence of habitat on seed dispersal by ants. Here we investigated the influence of neighboring seeds on seed removal in two coexisting myrmecochorous species (Epimedium pubescens and Helleborus thibetanus) from temperate deciduous forests of Qinling Mountains, central China, by examining (1) the potential role of ants and rodents and (2) whether the neighboring seed effect differed between forest edge and interior. We found that, presence of the higher-ESMR (elaiosome: seed mass ratio) E. pubescens did not significantly affect seed removal of the lower-ESMR H. thibetanus. By contrast, the presence of H. thibetanus decreased the seed removal rates of E. pubescens, with only a significant effect in rodent exclusion (ant alone) rather than in both ant exclusion (rodent alone) and full access (rodent+ant). Moreover, we found that those effects were not significantly different between the forest edge and the interior, which may be attributed to a similar pattern of overall seed-dispersing ant abundance in the two habitats. This suggested that neighboring seeds could influence seed removal of the focal plant depending on the absence of rodents; when rodents were present, the interaction of rodents and ants rendered no influence of neighboring seeds on seed removal. Our results show that the neighborhood effect was regulated by both dispersers and predators, and this effect was not context-dependent at a small spatial scale. This study highlights the importance to understand the effect of shared seed-removing animals and habitat context to assess the neighboring seed effect on plant-animal interactions.

Investment in reward by ant-dispersed plants consistently selects for better partners along a geographic gradient.

Seed dispersal by ants (myrmecochory) is an asymmetric, presumably mutualistic interaction, where a few ant species benefit many plants. Myrmecochorous plants express specialized adaptations, most notably a large elaiosome, which promote interactions with efficient seed dispersers while decreasing interactions with poor dispersers, resulting in de facto partner choice. However, because variation in plants’ investment in reward and ant response to them may vary spatially and temporally, it is unclear whether such specialization is consistent along geographic gradients; especially towards myrmecochory’s range margin. To answer this question on context-dependent partner choice, we first estimated variation in reward investment by co-occurring myrmecochores along a steep environmental gradient in a Mediterranean region. Second, we tested whether variation in plant investment in reward was positively and consistently correlated with the quality of dispersal plant received along the same gradient. Using in situ cafeteria experiments, we simultaneously presented diaspores of locally co-occurring myrmecochorous species to ants of two guilds representing high- and low-quality dispersers. We then recorded ant-seed behaviour, seed preference and seed removal rates for each ant guild. We found both overall and within-site high variation among plant species in the total and relative investment in elaiosomes. Both ant guilds removed substantial proportion of the seeds. However, scavenging ants (high-quality dispersers) clearly preferred diaspores with larger elaiosomes, whereas granivorous ants (low-quality dispersers) exhibited no preference. Furthermore, both the variation in plant traits and the corresponding response of different ant guilds were consistent along the studied geographic gradient. This consistency holds even when granivores, which removed seeds in a non-selective fashion and provided apparently low-quality seed dispersal services, were, at least numerically, the dominant ant guild. This dominance and the consistency of the partner choice shed light on the functionality of elaiosomes at the margins of myrmecochory’s distribution.

Diaspores of myrmecochorous plants as food for certain spiders

Spiders eating diaspores (seeds and fruits) from myrmecochorous plants – i.e. those adapted to distribution by ants – is recorded here for the first time as a new case of herbivory in these typical predators. Having found seeds of Costus dubius (Afzel.) K. Schum. (1904) trapped in the web of a Parasteatoda spider (Theridiidae), tests with available myrmecochorous seeds and spiders in the greenhouses of the Botanical garden of the P. J. Safarik University in Kosice (Slovakia) were carried out. Parasteatoda spiders can actively collect C. dubius seeds near their webs and feed on them for a long time. Diaspores with elaiosomes (nutrient-rich appendages) from five other myrmecochorous plant species thrown directly into webs of Parasteatoda sp. and Uloborus plumipes Lucas, 1846 (Uloboridae), another spider species very abundant at this location, were also consumed. These initial observations show that the special chemical composition of elaiosomes, which imitates insect prey primarily for ants, can be attractive for some spider species too. Considering the tested taxa, in the case of Uloboridae contact with such food sources is improbable in their typical niches. However, at least some Theridiidae could also consume myrmecochorous diaspores in nature, especially if they are near source plants or paths of ants transporting these diaspores.

Asynchrony between ant seed dispersal activity and fruit dehiscence of myrmecochorous plants.

Phenological mismatch has received attention in plant-pollinator interactions, but less so in seed dispersal mutualisms. We investigated whether the seasonal availability of myrmecochorous seeds is well matched to the seasonal activity patterns of seed-dispersing ants. We compared seasonal timing of seed removal by a keystone seed-dispersing ant, Aphaenogaster rudis, and fruit dehiscence of several species of plants whose seeds it disperses in a deciduous forest in southern Ontario, Canada. We examined the timing of elaiosome "robbing" by the nonnative slug Arion subfuscus and tested whether seed removal by ants declines in response to supplementation with additional elaiosome-bearing seeds (ant "satiation"). Seed removal from experimental depots peaked early in the season for all plant species and correlated with temperature. In contrast, elaiosome robbing by slugs increased late in the season and thus may disproportionately affect plants with late-dehiscing fruits. Ant colonies removed seeds at similar rates regardless of seed supplementation, indicating that satiation likely does not impact seasonal patterns of seed dispersal in this system. Fruits of the five myrmecochorous plant species in our study dehisced at discrete intervals throughout the season, with minimal overlap among species. Peak dehiscence did not overlap with peak seed removal for any plant species. Fruit dehiscence of myrmecochorous plants and peak ant seed dispersal activity occur asynchronously. Whether future climate warming will shift ant and plant phenologies in ways that have consequences for seed dispersal remains an open question.

The Preference of Some Myrmecochorous Plants of Forest Stands by Red Wood Ant (Formica rufa L.)—Experiment on Seeds with Elaiosomes

The paper is aimed in ants’ preference among seeds with elaiosomes. Seeds with elaiosomes of plants Asarum europaeum, Viola arvensis, Symphytum officinale, Chelidonium majus, and Ficaria verna were offered to red wood ants (Formica rufa) near two observed anthills. Monitored characteristics were the number of seeds collected by ants depending on the plant species, the presence of elaiosome, the orientation and the distance from anthill. The obtained data were processed by factorial ANOVA including PCA analysis. Seeds without elaiosomes were less preferred than the seeds with elaiosomes at statistical level. This experiment confirmed that elaiosomes attached to the seeds had significantly influenced transport of seeds by red wood ants. On the contrary, the influence of orientations (north–south) between seeds and the anthill were not proved. A distance of seeds from the anthill may play a certain role, but the results were not significant. Data indicated that ants had preferred seeds with elaiosomes of two plant species (A. europaeum and V. arvensis) from five species offered. The authors recommend to store seeds in a freezer before a similar experiment, because the elaisomes from different plant species will be fresh.

Diminishing importance of elaiosomes for acacia seed removal in non-native ranges

Myrmecochorous plants produce seeds with lipid-rich appendages (elaiosomes) which act as a reward for seed-dispersing ants. Seed dispersal is important for exotic species, which often need to establish new mutualistic interactions in order to colonize new non-native habitats. However, little is known about the importance of elaiosomes for seed removal in many of their non-native ranges. We studied ant–seed interactions of elaiosome-bearing and elaiosome-removed seeds of the Australian trees Acacia dealbata and Acacia longifolia in order to assess the relative importance of elaiosomes for seed removal between their native (Australia) and non-native (Portugal) ranges. In Portugal, we also studied the co-occurring native plant species with myrmecochorous seeds, Pterospartum tridentatum and Ulex europaeus, across three contiguous levels of acacia invasion: control (i.e. no acacia), low, and high acacia tree density. Acacia seeds were successfully removed by ants in their non-native region by a diversified assemblage of ant species, even in sites where native plants interacted with only one specialized ant species. In the invaded range, diminishing relative importance of elaiosomes was associated with changes in the ant community due to acacia invasion, and for A. dealbata, ant species richness decreased with increasing acacia tree density. Although seed removal was high for both acacia species, the importance of elaiosomes was proportionally lower for A. dealbata in the non-native region. Native plant species experienced significant reductions in seed removal in areas highly invaded by acacia, identifying another mechanism of displacement of native plants by acacias.

Tasty rewards for ants: differences in elaiosome and seed metabolite profiles are consistent across species and reflect taxonomic relatedness.

Diaspores of myrmecochorous plants consist of a seed (or fruit) and an attached appendage (elaiosome) which attracts ants. The elaiosome is a food resource for ants, whereas the seed is an energy source for subsequent germination and plant establishment. Although myrmecochory occurs in many phylogenetically unrelated lineages, multiple phylogenetic lineages display similar variation in elaiosome and seed metabolite composition due to convergent evolution. We focused on four families (Amaryllidaceae, Boraginaceae, Papaveraceae and Poaceae) each represented by two species from different genera. Diaspores of three populations per species were sampled and concentrations of 60 metabolites from five groups (amino acids, fatty acids, organic acids, polyols and sugars) were determined for both elaiosomes and seeds. Variability in metabolite composition was decomposed by hierarchical ANOVA and variation partitioning using redundancy analysis (reflecting both species nested within families, crossed with seed vs. elaiosome). Differences in the metabolite composition of elaiosomes and seeds were consistent across multiple phylogenetic origins (with more pronounced differences at the level of individual metabolites than at the level of metabolite groups) and supported the idea of convergent evolution under strong selection pressure. Elaiosomes contained higher amounts of easily digestible metabolites (especially amino acids) than seeds. Fatty acids were not more concentrated in elaiosomes, which contradicts the literal translation of "elaiosome" (= oil body). The differentiation of metabolite composition closely reflected taxonomic relatedness, particularly at the family level. Differences among populations within species were small, so the metabolite composition can thus be considered as a trait with relatively low intraspecific variability.

From dispersal to predation: A global synthesis of ant-seed interactions.

Ant–seed interactions take several forms, including dispersal, predation, and parasitism, whereby ants consume seed appendages without dispersal of seeds. We hypothesized that these interaction outcomes could be predicted by ant and plant traits and habitat, with outcomes falling along a gradient of cost and benefit to the plant. To test this hypothesis, we conducted a global literature review and classified over 6,000 pairs of ant–seed interactions from 753 studies across six continents. Linear models showed that seed and ant size, habitat, and dispersal syndrome were the most consistent predictors. Predation was less likely than parasitism and seed dispersal among myrmecochorous plants. A classification tree of the predicted outcomes from linear models revealed that dispersal and predation formed distinct categories based on habitat, ant size, and dispersal mode, with parasitism outcomes forming a distinct subgroup of predation based on seed size and shape. Multiple correspondence analysis indicated some combinations of ant genera and plant families were strongly associated with particular outcomes, whereas other ant–seed combinations were much more variable. Taken together, these results demonstrate that ant and plant traits are important overall predictors of potential seed fates in different habitat types.

Field experiments show contradictory short‐ and long‐term myrmecochorous plant impacts on seed‐dispersing ants

1. Some interactions previously described as mutualistic were revealed to be commensal or parasitic in subsequent investigations. Ant‐mediated seed dispersal has been described as a mutualism for more than a century; however, recent research suggests that it may be commensal or parasitic. Plants demonstrably benefit from ant‐mediated seed dispersal, although there is little evidence available to demonstrate that the interaction benefits long‐term ant fitness.2. Field experiments were conducted in temperate North America focused on a key seed‐dispersing ant. All herbaceous plants were removed from a forest understorey for 13 years, and supplemented ant colonies with large elaiosome‐bearing seeds aiming to examine potential long‐ and short‐term myrmecochorous plant benefits for the ants.3. If elaiosome‐bearing seeds benefit ants, suggesting a mutualistic relationship, it is expected that there would be greater worker and/or alate abundance and greater fat reserves (colony lipid content) with seed supplementation (short‐term) and in areas with high understorey herb abundance.4. Short‐term seed supplementation of ant colonies did not result in an increase with respect to numbers or fat stores, although it did prompt the production of colony sexuals, which is a potential fitness benefit. In the long term, however, there was no positive effect on the ants and, instead, there were negative effects because the removal of elaiosome‐bearing plants corresponded with greater colony health.5. The data obtained in the present study suggest that the ant–plant interaction ranged from occasionally beneficial to neutral to overall negative for the ant partner. Such results did not support considering the interaction as a mutualism. Collectively, the data suggest the need to reconsider the nature of the relationship between these ants and plants.

Seed manipulation by ants: disentangling the effects of ant behaviours on seed germination

1. Seed manipulation by ants can play a key role in seed germination through two main behaviours: elaiosome detachment and seed scarification. Despite the fact that these behaviours are commonplace, their effects have only been quantified independently, and their consequences on seed germination remain controversial.2. Here we experimentally investigate the effects of ant manipulation on seed germination, disentangling the contributions of these two ant behaviours to this process. To do so, under laboratory conditions, we studied the effects of seed manipulation by Acromyrmex subterraneus on germination of seeds from Mabea fistulifera, a myrmecochorous plant. We established six experimental treatments: (i) unmanipulated seeds; (ii) ant‐manipulated seeds with the elaiosome detached and scarified; (iii) ant‐manipulated seeds with the elaiosome detached and non‐scarified; (iv) hand‐manipulated seeds with the elaiosome remaining and scarified; (v) hand‐manipulated seeds with the elaiosome detached and scarified; and (vi) hand‐manipulated seeds with elaiosome detached and non‐scarified.3. We found that both elaiosome detachment and seed scarification decreased seed germination rates. Moreover, there was no difference in germination rates whether the seeds were manipulated by researcher's hand or by ants, suggesting a lack of other ant‐manipulation effects on seeds.4. The present study shows that manipulation by A. subterraneus can exert negative effects on germination of a myrmecochorous seed. Accordingly, we suggested that studies evaluating the benefits of myrmecochory for plants, based only on seed removal amount and distance, may be overestimating those benefits. Our results contribute to the understanding of the potential mechanisms influencing plant recruitment, especially for myrmecochorous plants inhabiting tropical forests.

Interaction between a threatened endemic plant (Anchusa crispa) and the invasive Argentine ant (Linepithema humile)

Seed dispersal mutualisms are essential to ensure the survival of diverse plant species and communities worldwide. Here, we investigated whether the invasive Argentine ant can replace native ants by fulfilling their functional role in the seed dispersal of the rare and threatened endemic myrmecochorous plant, Anchusa crispa, in Corsica (France). Our study addressed the potential of Linepithema humile to disperse elaiosome-bearing seeds of A. crispa, examining L. humile’s effects on (1) the composition of communities of ants removing seeds, (2) the number of seed removals, (3) seed preference, (4) the distance of seed dispersion, and (5) seed germination. We caught seven native species at the control site, but only the Argentine ant at invaded sites. L humile removed A. crispa seeds in greater numbers than did native ants, respectively 66 and 23%, probably due to their higher worker density. The invader was similar to native ants with respect to distance of seed transport. Finally, rates of seed germination were not significantly different between seeds previously in contact with either Argentine ants or not. Taken all together, these results suggest that the Argentine ant is unlikely to pose a threat to A. crispa population. These results have important implications for the management of this rare and threatened endemic plant and provide an example of non-negative interactions between invasive and native species.

Differential importance of consecutive dispersal phases in two ant‐dispersed Corydalis species (Papaveraceae)

Seed dispersal in myrmecochorous plants, in which a sequence of two or more steps is often involved, has profound effects on plant benefits. First, seeds mature or fall onto to the ground (primary dispersal), then ants transport them into nests (ant dispersal), and sometimes ants subsequently discard seeds out of nests (re‐dispersal). By neglecting one or the other of these phases, we might misjudge the benefits of myrmecochory to plants. Here, we investigated the difference between two common Chinese myrmecochorous plants, Corydalis incisa and C. wilfordii, in the importance of each dispersal step by examining 1) primary dispersal distance, 2) seed removal rates and dispersal distance by ants, and 3) frequency of seeds discarded out of nests and the re‐dispersal distance. We found that the mean primary dispersal distance of C. incisa was about eight times longer than that of C. wilfordii. The presence of an elaiosome increase the attractiveness of seeds to ants, and both the removal rate and dispersal distance were greater in C. wilfordii than in C. incisa. Two ant species, Pheidole noda and Pristomyrmex pungens are the major dispersers. Pheidole noda, the larger‐bodied ant species, discarded most seeds of both species out of nests, whereas Pr. pungens discarded only C. wilfordii seeds. The mean re‐dispersal distances of the two plant species were similar, but that of C. incisa and C. wilfordii were about threefold and fivefold shorter than the distances in the step of ant dispersal, respectively. In the field, no predators were found to interact with the discarded seeds in 72 h. Our results indicate that the importance of each dispersal phase differ between the two Corydalis species, and this difference is largely attributable to the differential role of ant identity and seed characteristics. It is concluded that re‐dispersal also needs to be considered in studies of myrmecochory.

Cover Caption: Seed dispersal by hornets

Seed dispersal by hornets is a rare dispersal mechanism in angiosperms. In this issue, Chen et al. (pp. 792–796) demonstrate that hornets are the primary and long‐distance seed dispersers in Stemona tuberosa, and ants act as the secondary dispersers and transport seeds to safe sites. This unique example of insect‐seed mutualism might be underestimated in myrmecochorous plants.

Seed re‐dispersal of four myrmecochorous plants by a keystone ant in central China

AbstractSeed re‐dispersal following initial harvesting by ants may have important implications for the distribution and fate of myrmecochorous seeds. However, the probability of seed re‐dispersed by ants and the effect it may have on subsequent survival appear variable, the functional role of diaspore, disperser and seed predator to the fate of discarded seeds remain unclear. To clarify the ecology, we compared the consequences of seed re‐dispersal by a keystone seed‐dispersing ant (Myrmica ruginodis Nylander) for four sympatric myrmecochorous plants common to the temperate deciduous forests in Qinling Mountains, central China. Plants varied in the probability of re‐dispersal and in elaiosome condition. Ants preferred seeds with residual elaiosomes, while rodents only consumed the two larger‐seeded species, regardless of the elaiosome presence. The scattered distribution of discarded seeds increased the probability of ant re‐harvesting and, to some extent, reduced rodent predation. Thus, difference in the probability of seed re‐dispersal and its subsequent effect on seed fate in relation to ants and rodents was attributed primarily to the elaiosome condition, seed size and seed spatial pattern. The results imply that seed re‐dispersal could affect the fitness of plants and ultimately influence the plant abundance and distribution pattern. This highlights the necessity to incorporate re‐dispersal into myrmecochory to advance our understanding of the benefits of myrmecochory to plants.

A Switch in Keystone Seed-Dispersing Ant Genera between Two Elevations for a Myrmecochorous Plant, Acacia terminalis

The dispersal capacity of plant species that rely on animals to disperse their seeds (biotic dispersal) can alter with changes to the populations of their keystone dispersal vectors. Knowledge on how biotic dispersal systems vary across landscapes allows better understanding of factors driving plant persistence. Myrmecochory, seed dispersal by ants, is a common method of biotic dispersal for many plant species throughout the world. We tested if the seed dispersal system of Acacia terminalis (Fabaceae), a known myrmecochore, differed between two elevations in the Greater Blue Mountains World Heritage Area, in southeastern Australia. We compared ant assemblages, seed removal rates of ants and other vertebrates (bird and mammal) and the dominant seed-dispersing ant genera. At low elevations (c. 200 m a.s.l) seed removal was predominantly by ants, however, at high elevation sites (c. 700 m a.s.l) vertebrate seed dispersers or seed predators were present, removing over 60% of seeds from experimental depots when ants were excluded. We found a switch in the keystone seed-dispersing ant genera from Rhytidoponera at low elevations sites to Aphaenogaster at high elevation sites. This resulted in more seeds being removed faster at low elevation sites compared to high elevation sites, however long-term seed removal rates were equal between elevations. Differences in the keystone seed removalist, and the addition of an alternate dispersal vector or seed predator at high elevations, will result in different dispersal and establishment patterns for A. terminalis at different elevations. These differences in dispersal concur with other global studies that report myrmecochorous dispersal systems alter with elevation.

An invasive slug exploits an ant-seed dispersal mutualism.

Plant-animal mutualisms, such as seed dispersal, are often vulnerable to disruption by invasive species. Here, we show for the first time how a non-ant invasive species negatively affects seed dispersal by ants. We examined the effects of several animal species that co-occur in a temperate deciduous forest-including native and invasive seed-dispersing ants (Aphaenogaster rudis and Myrmica rubra, respectively), an invasive slug (Arion subfuscus), and native rodents-on a native myrmecochorous plant, Asarum canadense. We experimentally manipulated ant, slug, and rodent access to seed depots and measured seed removal. We also video-recorded depots to determine which other taxa interact with seeds. We found that A. rudis was the main disperser of seeds and that A. subfuscus consumed elaiosomes without dispersing seeds. Rodent visitation was rare, and rodent exclusion had no significant effect on seed or elaiosome removal. We then used data obtained from laboratory and field mesocosm experiments to determine how elaiosome robbing by A. subfuscus affects seed dispersal by A. rudis and M. rubra. We found that elaiosome robbing by slugs reduced seed dispersal by ants, especially in mesocosms with A. rudis, which picks up seeds more slowly than M. rubra. Taken together, our results show that elaiosome robbing by an invasive slug reduces seed dispersal by ants, suggesting that invasive slugs can have profound negative effects on seed dispersal mutualisms.

Chemical composition of diaspores of the myrmecochorous plant Stemona tuberosa Lour

Diaspores of myrmecochorous plants often include nutrient rich elaiosomes, which are known as appendages of seeds to attract ants for seed dispersion. The benefits of myrmecochory were investigated thoroughly in previous studies, such as, the diaspores may be carried to the ant nests where the elaiosomes are consumed and the seeds are discarded unharmed. However, it remained unclear whether the secondary dispersers could shape the traits of diaspores in myrmecochory. In this study, we analyzed the nutritional quality of seeds and their corresponding elaiosomes of the myrmecochorous plant Stemona tuberosa (Stemonaceae), whose diaspores are dispersed by ants and/or hornets. Our results show significant differences in the quantitative pattern of nutrients between seeds and elaiosomes, respectively. The elaiosomes of S. tuberosa contain significantly higher concentration of proteins, free fatty acids, free amino acids, soluble carbohydrates, and micronutrients than the seeds. The low mass ratio of seed/elaiosomes in S. tuberosa compared to other myrmecochorous species imply that seed dispersal by hornets might be discriminated from seed dispersal by ants. In conclusion, we suggest that hornets and ants obtain the essential nutrients from the elaiosomes of S. tuberosa and these rewards contribute to shape the hornet/ant-plant mutualism.

Adaptive Advantage of Myrmecochory in the Ant-Dispersed Herb Lamium amplexicaule (Lamiaceae): Predation Avoidance through the Deterrence of Post-Dispersal Seed Predators.

Seed dispersal by ants (myrmecochory) is found worldwide, but the benefits that plants obtain from this mutualism remain uncertain. In the present study, we conducted laboratory experiments to demonstrate seed predator avoidance as a benefit of myrmecochory using the annual ant-dispersed herb Lamium amplexicaule, the disperser ant Tetramorium tsushimae, and the seed predatory burrower bug Adomerus rotundus. We compared the predation intensity of Lamium amplexicaule seeds by Adomerus rotundus under the presence or absence of Tetramorium tsushimae. Both the number of seeds sucked by Adomerus rotundus adults and the feeding duration of sucked seeds by nymphs were significantly reduced in the presence of ants. This effect was most likely due to the behavioral alteration of Adomerus rotundus in response to the ant presence, because ants seldom predated Adomerus rotundus during the experiment. Our results demonstrated that the presence of ants decreases post-dispersal seed predation, even when the ants do not bury the seeds. The present study thus suggests that the non-consumptive effects of ants on seed predators benefit myrmecochorous plants.