Study indicates symbiotic species can reconnect after separation

A study by UC Berkeley researchers is leading to new evolutionary knowledge of how symbiotic species can reestablish a connection after being geographically separated.

The study — published Sept. 7 in the journal Biology Letters — focuses on leafflower trees and leafflower moths, which are mutually dependent. However, a study by UC Berkeley researchers in collaboration with the French Polynesia Terrestrial Arthropods survey and the Moorea Biocode Project found leafflower trees but no leafflower moths on 15 of the 17 islands in French Polynesia.

David Hembry, co-author of the study and a graduate student in the campus Department of Environmental Science, Policy and Management, said these findings shed new light on the island biodiversity theory, which describes how highly specialized and dependent species would die out on isolated islands.

“It seemed mysterious,” he said. “I thought maybe the trees had evolved.”

The results of the three-year-long study led to the discovery that the trees did not in fact evolve but have somehow survived and repopulated without the aid of the leafflower moths. However, the moths have been able to symbiotically reconnect with the leafflower trees on some of the islands.

“My guess is that the moths are good at getting caught in the wind and blow about, and periodically the moths and trees find each other,” Hembry said, who spent a year and a half in French Polynesia documenting leafflower trees as part of this study.

The study showed that the moths are consistently finding the leafflower trees on every island, demonstrating that the mutualism between two species can be broken and reconnected.

“I think this will force us to realize that a lot of these connections can be novel,” said George Roderick, UC Berkeley professor in the Department of Environmental Science, Policy and Management who was involved in the study. “The connections between species are not as constrained as we were thinking. It shows us that some of these associations that we thought took millions of years to establish can form and reform if you get the right species together.”

As of now, scientists are unsure of the reason as to how the leafflower trees continue to survive without the leafflower moths, Hembry said. However, he said that an unlikely but possible explanation is that the trees are being pollinated by another species or  are reproducing asexually.

The next step in the research is to analyze the DNA from the different subspecies of leafflower trees in order to reconstruct the co-evolutionary history of the leafflower trees and the leafflower moths, which will help scientists understand the process of how symbiosis between species promotes diversification, according to Hembry.

“This will be a model system in evolutionary biological research,” Hembry said. “There will be a lot of things the leafflower trees and leafflower moths will be able to teach us. This will help us understand co-evolution and symbiotic relationships.”