Myrmecochory

Myrmecochory is the dispersal of seeds by ants. Most myrmecochorous plants produce seeds with elaiosomes or "food bodies", structures attached to the seed which are rich in lipids, amino acids or other nutrients and are attractive to ants. The seed with its attached elaiosome is collectively known as a diaspore. Seed dispersal by ants is typically accomplished when foraging workers carry diaspores back to the nest, after which the elaiosome is removed or fed directly to ant larvae. Once the elaiosome is consumed, the seed is usually discarded in underground middens or ejected from the nest. Although diaspores are seldom distributed far from the parent plant, the plant benefits through dispersal to favourable locations for germination as well as escape from seed predation.

A general introduction to this topic is found in chapter 14 of The Ants.

See myrmecochorous plants for additional details concerning specific plant species.

It should be noted that ants also remove non-myrmecochorous seeds. Anjos et al. (2020) found at least 13 ant genera removing 48 plant species across 12 countries. Their results highlight the ability of ants to remove more shrubs and small-sized diaspores (seeds). Regarding the diaspore removal distance, the ants can be crucial for the dispersal of tree diaspores and in the savanna ecosystems. Finally, considering the biodiversity crisis, the ants may play an even more important role than appreciated in diaspores dispersal.

Diplochory
There are plants that have developed a combination of two different means of moving seeds away from the parent plant, and these two strategies occur sequentially. One example of this is ballistic-ant diplochory. Plants using this dispersal syndrome first release their seeds via an explosive ejection, i.e., ballistic dispersal or ballochory, and then the seeds are further dispersed by ants. (see Chen et al. 2019)

Elaiosome
Elaiosomes are fleshy structures that are attached to the seeds of many plant species. The elaiosome is rich in lipids and proteins, and may be variously shaped. They develop in various ways either from seed tissues (chalaza, funiculus, hilum, raphe-antiraphe) or from fruit tissues (exocarp, receptacle, flower tube, perigonium, style or spicule). The various origins and developmental pathways apparently all serve the same main function, to attract ants. Because elaiosomes are present in at least 11,000, but possibly up to 23,000 species of plants, elaiosomes are a dramatic example of convergent evolution in flowering plants.

2019

 * Chen, S. C., A. H. Pahlevani, L. Malikova, R. Riina, F. J. Thomson, and I. Giladi. 2019. Trade-off or coordination? Correlations between ballochorous and myrmecochorous phases of diplochory. Functional Ecology. 33:1469-1479. doi:10.1111/1365-2435.13353

The combination of two dispersal syndromes (diplochory) brings additional benefits to seeds, yet the relative costs and benefits of the two phases are poorly understood. Our goal is to provide the first quantification to test the long-standing assumption that there are trade-offs between the two phases in ballistic-ant diplochory. Dispersal investment data were empirically measured for 91 Euphorbiaceae species across different regions of the world. Dispersal distance data of ballochory (seed dispersal by explosion), myrmecochory (seed dispersal by ants) and diplochory was collated from the literature for 210 records (148 species from 44 families). The data were analysed using Model II regression, Kolmogorov-Smirnov test and t test, complemented by phylogenetic comparative approaches. Across diaspores of diplochorous species, the relative investment in myrmecochory increased more than that in ballochory. Fruit coat mass and elaiosome mass covaried in an allometric manner, regardless of seed mass. Diplochorous diaspores were significantly heavier than diaspores dispersed solely by ballochory. Dispersal distances of the two diplochorous phases were independent and comparable to that of sole ballochory or sole myrmecochory. Our results do not support a trade-off, but a coordinated dispersal strategy between the two diplochorous phases. Large diaspores may evolve diplochory to overcome dispersal difficulties in term of dispersal distance. As the most comprehensive study of ballistic-ant diplochory, our findings advance the understanding of the relative importance of the two phases in diplochory. A plain language summary is available for this article.


 * Meadley-Dunphy, S.A., Prior, K.M. & Frederickson, M.E. 2019. Invasive ants disperse seeds farther than native ants, affecting the spatial pattern of seedling recruitment and survival. Oecologia 10.1007/s00442-019-04553-3

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.

2018

 * Fernandes, T. V., L. N. Paolucci, F. M. S. Carmo, C. F. Sperber, and R. I. Campos. 2018. Seed manipulation by ants: disentangling the effects of ant behaviours on seed germination. Ecological Entomology. 43:712-718. doi:10.1111/een.12655

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.


 * Miller, C. N. and C. Kwit. 2018. Overall seed dispersal effectiveness is lower in endemic Trillium species than in their widespread congeners. American Journal of Botany. 105:1847-1857. doi:10.1002/ajb2.1188

Premise of the Study: Comparing ecological attributes of endemic species with related, widespread species can reveal differences accounting for rarity. Forests of the southeastern United States are home to many range‐restricted endemic and widespread species of Trillium, a genus of ant‐dispersed herbs. Evidence suggests that aspects of seed‐related life history stages are often correlated with plant rarity, but few studies have tested whether the process of seed dispersal differs for endemic and widespread species. To address this question, we compared aspects of seed dispersal effectiveness (SDE) for three sympatric, widespread endemic Trillium species pairs. Methods: We observed seed dispersal for Trillium species pairs by ants at eight sites, recorded numbers of seeds dispersed and dispersal distances, and described disperser interactions. To test disperser preference, we presented seeds of each pair to captive colonies of Aphaenogaster picea, a keystone disperser. Seeds were assigned scores based on worker behavior, and we recorded proportions of seeds dispersed after 1 h and 24 h. Key Results: Field observations yielded some significant within‐pair differences. Ants dispersed more seeds of widespread species for all pairs, although dispersal distances did not differ. In laboratory experiments, after 24 h, ants dispersed more seeds of widespread species into nests. Conclusions: Endemic Trillium species had lower overall SDE than did their widespread congeners. These findings add to the list of ecological and demographic challenges that face endemic plants when compared to common congeners. Lower SDE may negatively impact reproductive rates and the colonization of new habitats, which may contribute to patterns of endemism.


 * Montesinos, D., M. Correia, S. Castro, K. French, and S. Rodriguez-Echeverria. 2018. Diminishing importance of elaiosomes for acacia seed removal in non-native ranges. Evolutionary Ecology. 32:601-621. doi:10.1007/s10682-018-9959-y

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.


 * Rocha, M. L. C., P. F. Cristaldo, J. S. Cruz, J. J. M. Sacramento, D. V. Ferreira, and A. P. A. Araujo. 2018. Ants Associated with Turnera subulata (Turneraceae): Elaiosome Attraction, Seed Dispersion and Germination. Neotropical Entomology. 47:750-756. doi:10.1007/s13744-018-0616-5

Symbiosis between plants and ants include examples in which the plant provides shelter and/or food for ants that, in turn, act in the defense or in the dispersion of seeds from the host plant. Although traditionally referred as mutualistic, the results of these interactions may vary with the ecological context in which patterns are involved. A range of species have facultative association with Turnera subulata (Turneraceae). Here, using behavioral bioassays, we investigated the effects of the most frequent ant species associated with T. subulata (Brachymyrmex sp.1, Camponotus blandus (Smith), Dorymyrmex sp.1, Crematogaster obscurata Emery, and Solenopsis invicta Buren) in the dispersion of plant host seeds and in the number of seedlings around the associated ant nests. We also evaluated the effects of these ant species in the germination of T. subulata seeds, in the consumption of elaiosome, and in the attractiveness to elaiosome odor. Our results showed that the ant species associated with T. subulata presented variation in the attraction by the odor and in the rate of consumption of the elaiosomes. However, none of the ant species studied contributed significantly to the increase of seed germination and seedling growth. Our results suggest that the consumption of the elaiosome by ant species is not a determinant factor to the success of germination of T. subulata. However, such species could contribute indirectly to seed germination by carrying seeds to sites more fertile to germination. In general, our results help to elucidate the results of ecological interactions involving ants and plants.


 * Zhu, Y. and D. Wang. 2018. Leaf Volatiles from Two Corydalis Species Lure a Keystone Seed-dispersing Ant and Enhance Seed Retrieval. Sociobiology. 65:370-374. doi:10.13102/sociobiology.v65i3.2726

It has been reported that a suit of plant traits can regulate the ant-seed interaction and subsequently affect the seed dispersal. However, the role of plant volatiles in attracting the ants for seed dispersal remains little examined. We used a Y-tube olfactometer to test behavior response of a keystone seed-dispersing ant (Pristomyrmex pungens Mayr) (=Pristomyrmex punctatus) to leaves and seeds of five co-occurring myrmecochorous Corydalis species (C. wilfordii Regel, C. racemosa (Thunberg) Persoon, C. sheareri S. Moore, C. balansae Prain and C. incisa (Thunberg) Persoon). Of the five species, only C. wilfordii and C. racemosa leaves emits heavily volatiles. We also performed seed cafeteria experiments to assess the effect of leaf volatiles from C. racemosa on seed retrieval by presenting simultaneously the seeds near the fresh leaf and the leaf immersed by diethyl ether both in the field and lab. The experiment using Y-tube showed that the ants were only significantly attracted by the fresh leaves of two species, C. wilfordii and C. racemosa. The cafeteria experiments showed that ants spent less time to detect the C. racemosa seeds which were near the fresh leaf, and transported these seeds more quickly. This indicated that the leaf volatiles can function as an attractant for the dispersing ants, and ant preference in turn enhance the seed retrieval. The findings reveal that leaf volatiles can play an important but underestimated role in shaping the ant-seed dispersing interactions.

2017

 * Pirk, G. I. and J. L. de Casenave. 2017. Ant interactions with native and exotic seeds in the Patagonian steppe: Influence of seed traits, disturbance levels and ant assemblage. Plant Ecology. 218:1255-1268. doi:10.1007/s11258-017-0764-4

Invasive plants may establish strong interactions with species in their new range which could limit or enhance their establishment and spread. These interactions depend upon traits of the invader and the recipient community, and may alter interactions among native species. In the Patagonian steppe we studied interactions of native ant assemblages with seeds of native and exotic plants, and asked whether ant–seed interactions differ with seed types and disturbance levels and whether the amount and type of ant–seed interactions can be predicted if both ant and seed traits are known. To characterize and quantify ant–seed interactions, we offered baits with large seeds of Pappostipa speciosa (native) and medium-sized elaiosome-bearing seeds of Carduus thoermeri (exotic), near and far from a road (high vs. low disturbed areas), and compared ant abundance and composition between areas. Interaction frequency was the highest for C. thoermeri seeds far from the road. Composition of ants interacting with C. thoermeri in these areas differed from that near the road and from that interacting with native seeds. Ant composition and abundance were similar between areas, but some species interacted more with exotic seeds in low disturbed areas. Ant foraging type predicted ant–seed interactions since the abundance of seed harvesters was positively correlated to interactions with P. speciosa, and that of generalists and predators, with interactions with C. thoermeri. The high interaction of ants with exotic seeds in low invaded areas suggests that ant activity could influence plant invasion, either by predating or dispersing seeds of invasive plants.

2014

 * Zhu, Y. & Wang, D. (2014). Seed dispersal of Corydalis wilfordii and C. racemosa (Papaveraceae): effect of ant foraging and behavior and seed characteristics. Acta Ecologica Sinica, 34: 4938-4942. (In Chinese with English abstract). doi:10.5846/stxb201301010005

Ant-mediated seed dispersal is ecologically important and geographically widespread. Previous studies revealed that seed-carrying ant may impact the rate of seed removal and dispersal distance, and the resultant short-term fate of seed, i.e. the seed location where the ants release after ant manipulation. The impact of ant recruitment and behaviour on seed dispersal of the cogeneric plant taxa, however, is relatively little known. We investigated the ant-mediated effect on seed dispersal of two cogeneric plants, Corydalis wilfordii and C. racemosa (Papaveraceae), in a subtropical evergreen forest at the Jiugongshan mountain (Hubei Province, China). The seed size of C. wilfordii is larger than that of C. racemosa, while the elaiosome/seed mass ratio of C. wilfordii is greater than that of C. racemosa. Being the mutual ant dispersers of the two Corydalis taxa, Pristomyrmex pungens (=Pristomyrmex punctatus) (with mass recruitment mode, i.e. to recruit a large number of ants to remove seeds when one ant found seed) and Prenolepis sphingthorax (=Nylanderia flaviabdominis) (with simple cooperative recruitmen mode, i.e. to recruit 5-30 ants to remove seeds when one ant found seed) played a varied role in seed dispersal of two plants. Pristomyrmex pungens carried about 44% of the C. wilfordii seeds transported by it to the nests, with the average dispersal distance of 1.85 m and the removal number of seeds per hour of 43.8, while the rest seeds were removed elaiosomes in situ and/or on the way to the nest. Prenolepis sphingthorax carried all seeds of the C. wilfordii to nests, with the average dispersal distance of 0.45 m and the removal number of seeds per hour of 7.3. In addition, both Pristomyrmex pungens and Prenolepis sphingthorax carried the all seeds of C. racemosa to the nests, with the average dispersal distance of 6.27 m and 6.65 m, and removal number of seeds per hour of 34.2 and 10.6 respectively. The results suggested that seed removal rate of ant with mass recruitment was higher than that of ant with simple cooperative recruitment. The seed dispersal distance and short-term seed fate differed between the two studied plants, depending on ant foraging strategies and behavior and seed characteristics. The discussion of the role of seed characteristics was also presented in the paper.