Myrmecochory ( (sometimes myrmechory); from ("ant") and ''khoreíā'' ("circular dance") is seed dispersal by

ant Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...

s, an ecologically significant ant–plant interaction with worldwide distribution. Most myrmecochorous plants produce seeds with

elaiosome Elaiosomes ( ''élaion'' "oil" + ''sóma'' "body") 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. Many plants have elaiosomes that attract ...

s, a term encompassing various external appendages or "food bodies" rich in

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the Proteinogenic amino acid, 22 α-amino acids incorporated into p ...

, or other

nutrient A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

s that 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

ant colony An ant colony is a population of ants, typically from a single species, capable of maintaining their complete lifecycle. Ant colonies are eusocial, communal, and efficiently organized and are very much like those found in other social Hymen ...

, after which the elaiosome is removed or fed directly to ant

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e. Once the elaiosome is consumed, the seed is usually discarded in an underground midden or ejected from the nest. Although diaspores are seldom distributed far from the parent plant, myrmecochores also benefit from this predominantly mutualistic interaction through dispersal to favourable locations for

germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, ...

, as well as escape from seed predation.

Distribution and diversity

Myrmecochory is exhibited by more than 3,000 plant

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

worldwideBeattie, A.J. and Hughes, L. (2002). “Ant–plant interactions” In Plant–Animal Interactions and Evolutionary Approach, (eds C. M. Herrera & O. Pellmyr), pp. 211–35. Blackwell Science, Oxford. and is present in every major

biome A biome () is a distinct geographical region with specific climate, vegetation, and animal life. It consists of a biological community that has formed in response to its physical environment and regional climate. In 1935, Tansley added the ...

on all continents except Antarctica. Seed dispersal by ants is particularly common in the dry heath and sclerophyll woodlands of

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

(1,500 species) and the South African fynbos (1,000 species). Both regions have a

Mediterranean climate A Mediterranean climate ( ), also called a dry summer climate, described by Köppen and Trewartha as ''Cs'', is a temperate climate type that occurs in the lower mid-latitudes (normally 30 to 44 north and south latitude). Such climates typic ...

and largely infertile soils (characterized by low

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

availability), two factors that are often cited to explain the distribution of myrmecochory.Westoby, Mark, L. Hughes, and B.L. Rice (1991). “Seed dispersal by ants; comparing infertile with fertile soils.” In Ant-plant interactions, Camilla R. Huxley and David F. Cutler (eds.), pp. 434–447, Oxford University Press, New York. Myrmecochory is also present in mesic forests in

temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

regions of the Northern Hemisphere (''i.e.'' in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and in eastern

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

), as well as in tropical forests and dry

desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...

s, though to a lesser degree.Buckley, R.C. (1982). “Ant-plant interactions: a world review” In Ant-plant interactions in Australia, Buckley R.C. (ed.), pp. 111–141, Dr W. Junk Publishers, The Hague. Estimates for the true

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

of myrmecochorous plants range from 11,000 to as high as 23,000 species worldwide, or about 5% of all

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

species.

Evolutionary history

Myrmecochory has evolved independently many times in a large number of plant families. A recent phylogenetic study identified more than 100 separate origins of myrmecochory in 55 families of flowering plants. With many independent evolutionary origins, elaiosomes have evolved from a wide variety of parent tissues. Strong selective pressure or the relative ease with which elaiosomes can develop from parent tissues may explain the multiple origins of myrmecochory. These findings identify myrmecochory as a prime example of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

. In addition, phylogenetic comparison of myrmecochorous plant groups reveals that more than half of the lineages in which myrmecochory evolved are more species-rich than their nonmyrmecochorous sister groups. Not only is myrmecochory a convergent trait, but it also promotes diversification in multiple flowering plant lineages.

Ecology

Myrmecochory is usually classified as a mutualism, but this is contingent on the degree to which participating species benefit from the interaction. Several different factors likely combine to create mutualistic conditions. Myrmecochorous plants may derive benefit from increased dispersal distance, directed dispersal to

-enriched or protected microsites, and/or seed predator avoidance. Costs incurred by myrmecochorous plants include the energy required to provision diaspores, particularly when a disproportionate investment is made of growth-limiting mineral nutrients. For instance, some Australian ''

Acacia ''Acacia'', commonly known as wattles or acacias, is a genus of about of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa, South America, and Austral ...

'' species invest a significant portion of their yearly

uptake in producing diaspores.Westoby, Mark., Barbara Rice, Julia M. Shelley, David Haig, and J.L. Kohen (1982). “Plants' use of ants for dispersal at West Head, New South Wales” In Ant-plant interactions in Australia, Buckley R.C. (ed.), pp. 75–87, Dr W. Junk Publishers, The Hague. Diaspores must also be protected from outright predation by ants. This is typically accomplished by the production of a hard, smooth testa, or seed coat. Few studies have examined the costs and benefits to ants participating in myrmecochory. Much remains to be understood about the selective advantages conferred upon myrmecochorous ants. No single

hypothesis A hypothesis (: hypotheses) is a proposed explanation for a phenomenon. A scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educated guess o ...

explains the evolution and persistence of myrmecochory. Instead, a combination of beneficial effects working at different spatiotemporal scales likely contribute to the viability of this predominantly mutualistic interaction. Three commonly cited advantages to myrmecochorous plants are increased dispersal distance, directed dispersal, and seed predator avoidance.

Dispersal distance

Increasing dispersal distance from the parent plant is likely to reduce seed mortality resulting from density-dependent effects. Ants can transport seeds as far as 180 m but the average is less than 2 m, and values between 0.5 and 1.5 m are most common. Perhaps due to the relatively limited distance that ants disperse seeds, many myrmecochores exhibit diplochory, a two-staged dispersal mechanism, often with ballistic projection as the initial mechanism, that can increase dispersal distance by as much as 50%. In some cases, ballistic dispersal distance regularly exceeds that of transport by ants. The dispersal distance achieved through myrmecochory is likely to provide an advantage proportionate to the spatial scale of density-dependent effects acting on individual plants. As such, the relatively modest distances ants transport seeds are likely to be more advantageous for myrmecochorous

shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...

s, forbs, and other plants of small stature.

Directed dispersal

Myrmecochorous plants may benefit when ants disperse seeds to nutrient-rich or protected microsites that enhance

and establishment of

seedling A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...

s. Ants disperse seeds in fairly predictable ways, either by disposing of them in underground middens or by ejecting them from the nest. These patterns of ant dispersal are predictable enough to permit plants to manipulate animal behaviour and influence seed fate,Hanzawa, F.M., Beattie, A.J., and Culver, D.C. (1988). “Directed dispersal: demographic analysis of an ant-plant mutualism”. The American Naturalist, 131(1): 1–13. effectively directing the dispersal of seeds to desirable sites. For example, myrmecochores can influence seed fate by producing rounder, smoother diaspores that inhibit ants from redispersing seeds after elaiosome removal. This increases the likelihood that seeds will remain underground instead of being ejected from the nest. Nest chemistry is ideally suited for seed germination given that ant colonies are typically enriched with plant nutrients such as phosphorus and

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

. This is likely to be advantageous in areas with infertile soils and less important in areas with more favourable soil chemistry, as in fertile forests. In fire-prone areas, depth of burial is an important factor for successful post-burn germination. This, in turn, is influenced by the nesting habits of the myrmecochorous ants. As such, the value of directed dispersal is largely context-dependent.

Seed predator avoidance

Myrmecochorous plants escape or avoid seed predation by granivores when ants remove and sequester diaspores. This benefit is particularly pronounced in areas where myrmecochorous plants are subject to heavy seed predation, which may be common. In mesic forest habitats, seed predators remove around 60% of all dispersed seeds within a few days, and eventually remove all seeds not removed by ants.Heithaus, E.R., Culver, D.C., and Beattie, A.J.. (1980). “Models of some ant-plant mutualisms”. The American Naturalist 116(3): 347–361. In addition to attracting ants, elaiosomes also appeal to granivores, and their presence can increase seed predation rates.

Nature of the interaction

Myrmecochory is traditionally thought to be a diffuse or facultative mutualism with low specificity between myrmecochores and individual ant species. This assertion has been challenged in a study of

Iberia The Iberian Peninsula ( ), also known as Iberia, is a peninsula in south-western Europe. Mostly separated from the rest of the European landmass by the Pyrenees, it includes the territories of peninsular Spain and Continental Portugal, compri ...

n myrmecochores, demonstrating the disproportionate importance of specific ant species in dispersing seeds. Ant-plant interactions with a single species of myrmecochore were recorded for 37 species of ants, but only two of these were found to disperse diaspores to any significant degree; the rest were seed predators or “cheaters” opportunistically feeding on elaiosomes ''in situ'' without dispersing seeds. Larger diaspores are hypothesized to increase the degree of specialization, since ant mutualists need to be larger to successfully carry the diaspore back to the nest. Ants, however, do not appear to form obligate relationships with myrmecochorous plants. Since no known ant species relies entirely on elaiosomes for their nutritional needs, ants remain generalist foragers even when entering into relationships with a more specialized myrmecochore. As with many other facultative mutualisms, cheating is present on both sides of the interaction. Ants cheat by consuming elaiosomes without transporting seeds or through outright seed predation. Myrmecochorous plants can also cheat, either by producing diaspores with nonremovable elaiosomes or by simulating the presence of a nonexistent reward with chemical cues. Ants are sometimes capable of discriminating between cheaters and mutualists as shown by studies demonstrating preference for the diaspores of noncheating myrmecochores. Cheating is also inhibited by ecological interactions external to the myrmecochorous interaction; simple models suggest that predation exerts a stabilizing influence on a mutualism such as myrmecochory.

Myrmecochory and invasive species

Myrmecochores are threatened by

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

in some ecosystems. For instance, the Argentine ant is an aggressive invader capable of displacing native ant populations. Since Argentine ants do not disperse seeds, invasions may lead to a breakdown in the myrmecochory mutualism, inhibiting the dispersal ability of myrmecochores and causing long-term alterations in plant community dynamics. Invasive ant species can also maintain seed dispersal in their introduced range, as is the case with the red fire ant in the Southeastern United States. Some invasive ants are also seed-disperses in their native range, such as the European fire ant, and can act as a high-quality disperser in their introduced range In South Africa, the Argentine ant has in some cases displaced native ants that disperse the seeds of

Fynbos Fynbos (; , ) is a small belt of natural shrubland or heathland vegetation located in the Western Cape and Eastern Cape provinces of South Africa. The area is predominantly coastal and mountainous, with a Mediterranean climate. The fynbos ...

plants like '' Mimetes cucullatus''. The Argentine ants don't take the seeds underground and leave them on the surface, resulting in ungerminated plants and the dwindling of Fynbos seed reserves after veld fires. Myrmecochorous plants are also capable of invading ecosystems. These invaders may gain an advantage in areas where native ants disperse invasive seeds. Similarly, the spread of myrmecochorous invaders may be inhibited by limitations in the ranges of native ant populations.

References

External links

* * {{Authority control Insect ecology Myrmecology Seeds Mutualism (biology)