Plants produce juicy, sweet fruit with secret seeds inside them so that fruit-eating mammals, from toucans to fruit bats to orangutans, are lured into taking a bite.
Then, these animals fly or roam far and wide and, once they’ve digested their meal, they poop out the fruit’s seeds together with the rest of their waste. In doing so, these hungry animals have helped plants, which cannot move, travel and disperse their seeds along a wider range.
This is at the base of how hundreds of ecosystems work, since the dawn of time. However, a growing body of research is starting to suggest that mammals and birds are far from the only ones shaping how seeds travel across the world and spread plant life to new nooks and crannies. Tiny, creepy-crawly insects and invertebrates play a crucial role, too.
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Ants are perhaps the most well-known seed-dispersing insects. But the seeds they spread aren’t from fruit. They spread seeds from particular plants that have special, little, ant-friendly oil bodies attached to the seed, known as elaiosomes.
The ants carry the seed to their nest, eat the elaiosome and discard the seed, either by carrying it to the surface or placing it into ‘rubbish piles’ deep underground, according to Prof Ellen Simms, an integrative biologist at the University of California, Berkeley.
Other insects are thought to help disperse seeds by pooping them out, like mammals and birds, but only for a special subset of plants. These are non-green plants that don’t harvest light but instead parasitise other plants or consume underground fungi to harvest the nutrients and energy they need.
For example, centimetre-long woodlice eat the small fruits of a ghostly, parasitic bell-shaped Asian plant called Monotropastrum humile. Then, they excrete over 30 per cent of the dust-like seeds
still intact enough to plant in the soil and grow according to research from earlier this year.
These tiny invertebrates set a new record for the smallest and lightest animals to partake in seed dispersal after ingestion. However, the seedlings still need the help of fungi to germinate successfully.
What’s more, researchers in New Zealand discovered that the Wētā cricket, a flightless native insect the size of a hamster, munches away at the seeds of plants such as mountain snowberries and then disperses them by pooping them out as they wander over large distances.
“I was amazed,” says biologist Kevin Burns from the Victoria University of Wellington, whose work helped discover the phenomenon. “In fact, it was contentious. It still is contentious.”
The humongous cricket likely stepped in to fill this unusual, surprising role in the ecosystem because the isolated island nation isn’t home to any of the ground-dwelling, fruit-eating mammals that take care of seed dispersal elsewhere in the world.
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Similarly, Japanese camel crickets eat and poop out the seeds of a leafy Asian shrub called Rhynchotechum discolor, according to a new study published last month.
The plant, found along moist, shaded forests, swamps, and thickets, has small, rounded, translucent, and fleshy fruits containing thousands of tiny seeds. Once the fruits plop to the ground, the crickets chomp away and then excrete pellets with more than 78 per cent intact seeds ready to germinate just with a tad of water.
This is the first evidence of insects acting as seed dispersers for a light-harvesting, green plant in regions where land-dwelling mammals are around to do the job themselves.
It is “quite groundbreaking” and “opens up a whole new world of possibilities,” says Prof Kenji Suetsugu, a botany researcher at Kobe University in Japan and lead author of the study.
This challenges the long-held notion that seed dispersal by insects is a special, unique case – their role may be much more widespread and ecologically important than previously understood.
Insects could be just as important as the more traditionally recognised dispersers, says Suetsugu. Because they are incredibly diverse, abundant, and small they can access a wider variety of areas than larger animals. Plus, plants might have evolved specific traits not just to attract birds or mammals, but also insects.
While some experts think it’s important not to get ahead of ourselves, as it might still be a rare phenomenon on a global scale, more research could upend everything we’ve known about seed dispersal.
It may well be the case that small insects are the unsung heroes and tiny engineers of many of the world’s ecosystems.
About our experts
Prof Ellen Simms is a biologist based at UC Berklee. Her work has been published in the journals BMC Ecology, Ecology Letters and Molecular Ecology.
Prof Kevin Banks is a field biologist based at Victoria University of Wellington. His work has been published in the journals Plant Ecology, Ecological Studies and Biotropica.
Prof Kenji Suetsugu is a biologist based at Kobe University. His work has been published in the journals Ecology, New Phytologist and The Journal of Plant Biology.
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