Solving the mystery of how Zamias live in the forest canopy

Zamia pseudoparasitica is an interesting plant, to say the least. Resembling a palm tree with short cones, this cycad is a relative of Zamias that existed 68.3 million years ago, when the dinosaurs were still around. 

Today, Zamia pseudoparasitica is the only member of its family in the world that does not live on the ground. Instead, it hangs onto tree branches by its roots about 10 to 20 meters up in the air. Zamia pseudoparasitica is found exclusively in the montane cloud forests of western Panama.

A new study from the Smithsonian Tropical Research Institute is beginning to unravel the mystery of Zamia pseudoparasitica, providing new clues about the plant’s history and how it persists in the forest canopy. 

The study began a few years ago – when STRI scientist Claudio Monteza and Senacyt-STRI intern and biologist Lilisbeth Rodríguez ran into each other at the Smithsonian research station on Barro Colorado Island in the Panama Canal. 

Rodríguez told Monteza about a research project she was conducting with Zamia pseudoparasitica under the supervision of Professor Juan Carlos Villarreal, a biologist from Laval University in Canada, and Kristin Saltonstall, an STRI staff scientist in Panama.

“My goal was to collect samples from different species of Zamias in the country,” said Rodríguez. “These samples would later be analyzed in the laboratory to find out what species of fungi and bacteria grow inside their leaves.”

Professor Villarreal explained that no one knew how this plant’s seeds were dispersed – it was still a mystery. To investigate, the researchers placed camera traps up in the trees to examine what mammal species interacted with the Zamia.

The traps were positioned in trees across three three protected areas where Zamia pseudoparasitica grows, including the Palo Seco Protected Forest, the Santa Fe National Park and the Omar Torrijos Herrera National Park in El Copé. In March, 2020, shortly before pandemic lockdowns began, the researchers collected the camera traps.

The footage may explain how Z. pseudoparasitica disperses in the trees and not on the ground like other Zamias. The experts found that seven different mammals visited tree branches where the plants were growing. Some of the animals did not pay attention to the Zamias. Capuchin monkeys, opossums and kinkajous inspected the cones, and sometimes licked the plants, but did not take the seeds.

Only one animal was observed at all three sites – the northern olingo, a nocturnal tree-dwelling mammal that is active high in the canopy and feeds primarily on fruit. These animals were seen inspecting and biting the cones of Z. pseudoparasitica when they were still closed and immature. Once the seeds were opened, the olingos collected up to four seeds at a time.

“It could be that the olingos are taking the seeds to what would be their den or perhaps to a seed bank,” explained Monteza. “If they are, which we don’t yet know for sure, it would help to explain why this is the only Zamia species that lives in the forest canopy.”

According to the researchers, this means that if the seeds are being stored in the canopy by olingos, they might end up in favorable places for germination.

“The montane forests of western Panama are very unique, filled with many species that aren’t found anywhere else,” said Kristin Saltonstall, co-supervisor of the project. “It’s exciting to document this interaction between such a special plant and an animal that is also poorly understood.”

“Z. pseudoparasitica is a true epiphyte; that is to say, it spends its entire life in the forest canopy,” said Monteza. “How it persists there is a mystery that perhaps we will begin to solve with these initial findings. It’s exciting because we can continue to the next phase by collecting more data; for example, it occurs to us that we can mark the seeds with bioluminescence, wait for the olingos to take them away and then search for the seeds at night.”

The study is published in the journal Ecology and Evolution.

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By Chrissy Sexton, Earth.com Staff Writer