Plants have coopted many animals to help them thrive and propagate. Ants may not be the best pollinators, but properly motivated they make precious porters for progeny.
Many wildflowers bloom in the spring thanks to ants. The tiny 6-legged gardeners have partnered with over 11,000 plants to disperse their seeds. The plants, in turn, pay for the service by attaching a calorie-laden “thank you” to each seed, similar to the fleshy fruits that reward birds and mammals for dispersing their shelled offspring.
Many ants eat seeds. But in the deciduous forests of Europe and North America, Australian dry woodlands, and South African shrublands called fynbos, a few dozen ant species spare the seeds for something better. Certain plants attach a nutritive glob called an elaiosome to their seed coats, which serves as lunch for the ants’ younglings and gives ants a handle on seeds that can be bigger than their heads.
Plants specifically design their elaiosomes to appeal to ant tastes. How plants know what an ant likes to eat is a mystery – but they certainly do.
Far from just spreading seeds, ants are active gardeners, preferring some seeds over others and keeping their charges safe from disease.
Like most ants, seed-dispersing ants secrete antimicrobial chemicals to clean themselves and their sisters. Seeds handled by ants get an antimicrobial treatment that pummels pathogens on the seeds.
Ants are picky when it comes to seeds. Those left behind have lower odds of prospering. “Being less preferred really has consequences,” says American evolutionary ecologist Judith Bronstein.
Trilliums are a genus of temperate flowering plants, with some 50 species in North America and Asia. The greatest diversity of trilliums is in the southern Appalachian Mountains in the southeastern United States.
Ants pick seeds based on specific combination and concentrations of oleic acid and other compounds made by a trillium. 20 of these chemicals are unique to trilliums.
Numbers tells the payoff to trilliums of carefully preparing enticing elaiosomes. “Widespread trillium species are preferred by seed-dispersing ants compared to rare trillium species,” notes American ecologist Kirsten Prior.
In places absent ants, seeds may not find their way to fertile ground. Ecosystems suffer. Lost ants means lost plants, as well as other life that depends upon that cooperative relationship.
Disruption to ant habitats can dissuade ants from coming back for a long time. “There are huge impacts of past land use,” says American ecologist Katie Stuble. Lack of ants could explain why secondary forests lack dense undergrowth, and why plants that rely on ants to disperse their seeds are scarce there.
“Ants perform important functions in ecosystems,” concludes American ecologist Melissa Burt. “Seed dispersal is just one of those.”
Elizabeth Pennisi, “Don’t crush that ant – it could plant a wildflower,” Nature (14 August 2020).
Ant photo by Alex Wild.