An orange, clay-like dirt lines the Panama Canal. Container ships are slowly towed through the expanse of water, crossing from the Atlantic to Pacific. Dense vegetation lines either side, a green tropical forest filled with immense biodiversity.
This is the second episode of the 2025 edition of Secret Beyond the Seed. Welcome back to the Panamanian tropical forest.
We are joining Utah State University Ph.D. Candidate Elsa Mini Jos in the forest as she searches for a specific group of plant species called Psychotria.
We pull up to the Smithsonian Institute’s Barro Colorado Island field station after a 45-minute boat ride through Gatun Lake. The station sits on the water’s edge and paths lead into the forest, allowing researchers access to a great diversity of life.
Jos leads me into the forest, up and down the steep hilly landscape, in search of Psychotria plants. She monitored the plant’s fruits as they began to ripen and now she is collecting them to analyze their nutrient content.
“I want to look at how fast fruits get eaten in the field, so essentially I want to understand how long they are exposed to any insect predators or pathogens that might attack these fruits once they're ripe,” Jos says.
The ripened fruits are eaten by small understory birds, like manakins and thrushes.
We walk further into the forest, finally spotting some ripe Psychotria. The dark red of the fruit stands out against the broad green leaves.
“You essentially track the fruits until they start ripening, and then you collect the fruits and freeze dry them, separate the pulp and seeds, and then grind them, and then you extract them for either secondary metabolites or for nutrients,” Jos explains.
Secondary metabolites are molecules produced by plants and animals that are not directly involved in growth or reproduction. They are often produced as defense mechanisms against predators but can also function to attract or otherwise mediate interactions with other species that result in mutual benefits.
Jerry Schneider, former postdoctoral scholar with the group, recently elucidated the diversity of secondary metabolites of Psychotria and closely related species, and Jos is now building off of that information to pinpoint the role of metabolites in defending fruit against fungi.
“The idea is these different fruits might have different nutrient content and then that can sort of affect how fast they might get eaten because they provide nutrients," Jos says.
Jos is interested in understanding the relationships between those fruit defenses, nutrient content and dispersal in Psychotria species, in the tribe Psychotrieae. The tribe Psychotrieae and closely related Palicoureeae, both in the family Rubiaceae, comprise a high diversity of plant species, which includes 21 closely related species that appear ecologically similar and are abundant on Barro Colorado island.
“So many of these species can coexist in a really small space. And at least from what we know now, they also share similar dispersers, manakins, thrushes, and a few other understory birds,” Jos says.
The booming call of mantled howler monkeys echoes throughout the forest. Rain soon starts to fall, lightly at first but it crescendos, drenching the plants and leaving a chill in the tropical forest. We come across fallen trees, brought down by great bouts of wind brought in by storms. The rain subsides as we head back to the field station for the night.
Jos’ work is part of a much larger research project on plant chemistry and dispersal in the Panamanian forest ecosystem. These Psychotria species complement another 50 plant species that Utah State University Associate Professor of Biology Noelle Beckman and her research team have collected and are in the process of analyzing for their work.
“There weren't too many people who are actively studying fruit chemistry and trying to understand the diversity of chemicals that fruit had and the evolutionary reasons for that, and how they might mediate interactions with other organisms, especially with respect to seed dispersal,” Beckman said.
In the next episode of Secret Beyond the Seed we will delve further into the evolutionary relationships between seed dispersers, like birds and bats, and plant chemistry.
This series is made possible by the support of the National Science Foundation.
