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KC Burns’ favorite research days are when he puts on his backpack and walks through the wilderness with no agenda. While on a hike on Australia’s Lord Howe Island, he came across a cluster of staghorn ferns. They are common potted plants, but in nature they grow in dense colonies that cling to treetops. In the scrub forest of the volcanic island, these treetops are at eye level.
Biologist at Victoria University of Wellington in New Zealand, Dr. “I almost looked beyond,” Burns said. Then he took a closer look and realized that the plants in the colony did different jobs to survive. Ferns growing higher had waxy leaves that seemed to direct rainwater towards the center of the colony. Further down, the ferns grew spongy leaves that were moist to the touch. Some plants did not reproduce at all—as if they had devoted their lives to collecting water for their neighbors’ entangled roots.
Dr. Burns realized that ferns work together as a kind of super-organism, perhaps like bees in the hive.
“I sat down and thought, oh my god”. said. In paper Published in Ecology last month, Dr. Burns and his co-authors argued that colonies of the staghorn fern Platycerium bifurcatum exhibit a type of collective behavior known as eusociality. Until now, scientists had accepted eusociality in some animal species, such as bees or ants, which only live in colonies and divide their labor.
To measure how ferns divide labor, the researchers sampled plants growing at different heights within 24 colonies. They counted two types of leaves on each plant. One species, which they call nest leaves, is round and often brown, gripping the tree like a palm. Other leaves are long, green, and forked like horns, and their undersides may grow spores that will become the next generation of ferns.
Plants closer to the top of each colony had more spore-bearing leaves. Plants near the bottom had more pitted, non-breeding nest leaves. About 40 percent of individual plants did not reproduce at all, as did worker bees.
Next, the scientists cut wedges from the nest leaves, dried them, then dipped them in water to measure how drenched they were. They found that the nest leaves at the bottom of the colony were more absorbent.
These spongy leaves can help keep the entire colony moist, as the colony’s roots grow in a tangled web. The scientists found that larger colonies (the largest they examined held 58 individual ferns) had more spore-bearing leaves per person. So living in a large group can improve the fitness of ferns.
For the most part, groups are families. Dr. “We quickly realized that genetics was important,” Burns said, because eusocial animals live in close groups.
When the researchers analyzed DNA from 11 fern colonies, they found that most plants within a colony were as closely related as possible: They were clones. Dr. New plants emerge from buds on the root systems of others, Burns said.
Being a clone “means that different individuals genetically align their interests,” said Guy Cooper, an evolutionary biologist at Oxford University. A plant also helps its own genes survive by helping a neighboring clone.
Dr. Cooper said he wanted to learn more about the life cycle of a colony and how interconnected individual ferns are.
Even though antler ferns aren’t as social as bees, “It was very nice to see that there can be similar kinds of complex social behavior in plants,” he said.
He also drew attention to the fact that some plants propagated by cloning themselves are considered as a single individual rather than many. For example, aspen trees produce huge clone gardens from a single root network. Nicknamed an aspen forest in Utah Pando is sometimes referred to as the world’s largest single organism., 106 acres.
Dr. “You have to ask more philosophical questions about whether they are different individuals in the beginning,” Cooper said of ferns. Perhaps ferns in a colony are more like limbs on a body than bees in a hive.
Cloning doesn’t explain the whole story of staghorn ferns. In some Lord Howe Island colonies, Dr. Burns and colleagues found unrelated plants. They don’t know how these ferns became part of treetop communities.
Biologist Karen Kapheim, who studies the evolution of social behavior in bees at Utah State University, says plants are some of the most resilient creatures on earth. Maybe it’s not surprising that a fern can also improve social tendencies, he said.
Science is revealing more and more about how plants come to be. Behave and contact, said Dr. Kapheim “I think adding social behavior to that fits with this new, emerging understanding of plants.”
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