'Living Fossil' Tree may Offer Clues to Past and Future Climate Change

by VR Sreeraman on Nov 2 2008 11:41 AM

With the help of a "living fossil" tree species, a researcher from the University of Michigan is trying to understand how tropical forests responded to past climate change and how they may react to global warming in the future.

The researcher in question is Christopher Dick, an assistant professor of ecology and evolutionary biology, in the University of Michigan.

Symphonia globulifera, which is referred to as the "living fossil", is a widespread tropical tree with a history that goes back some 45 million years in Africa.

"It is unusual among tropical trees in having a well-studied fossil record, partly because the oil industry uses its distinctive pollen fossils as a stratigraphic tool," said Dick.

About 15 to 18 million years ago, deposits of fossil pollen suggest, Symphonia suddenly appeared in South America and then in Central America.

Unlike kapok, a tropical tree with a similar distribution that Dick also has studied, Symphonia isn't well-suited for traveling across the ocean. Its seeds dry out easily and can't tolerate saltwater.

As to how did Symphonia reach the neotropics, Dick said that most likely the seeds hitched rides from Africa on rafts of vegetation, as monkeys did.

Even whole trunks, which can send out shoots when they reach a suitable resting place, may have made the journey.

Because Central and South American had no land connection at the time, Symphonia must have colonized each location separately.

Once Symphonia reached its new home, it spread throughout the neotropical rain forests.

By measuring genetic diversity between existing populations, Dick and coworker Myriam Heuertz of the Universite Libre de Bruxelles were able to reconstruct environmental histories of the areas Symphonia colonized.

"For Central America, we see a pattern in Symphonia that also has been found in a number of other species, with highly genetically differentiated populations across the landscape," Dick said.

"In many places, the forests were confined to hilltops or the wettest lowland regions. What we're seeing in the patterns of genetic diversity is a signature of that forest history," he added.

According to Dick, in the core Amazon Basin, which was moist throughout the glacial period, allowing for more or less continuous forest, less genetic diversity is found among populations.

"There's less differentiation across the whole Amazon Basin than there is among sites in lower Central America," he said.

The study is the first to make such comparisons of genetic diversity patterns in Central and South America.

"We think similar patterns will be found in other widespread species," Dick said.

"Learning how Symphonia responded to past climate conditions may be helpful for predicting how forests will react to future environmental change," he added.