Fall is officially here. As you head out to see North Carolina’s forests during their peak of color intensity, you may observe some local wildlife. While seeing animals such as rare birds, bears or flying squirrels can be exciting, you may also wonder just how all of these animals ended up living together in our forests, and where these forests came from in the first place.
Recently, I joined a team of scientists from Yale University and the New York Botanical Garden asking this question. Together we determined the origin of a prominent group of rain forest trees in Madagascar. The answer: They came from the sea, thousands of miles away on the other side of the Indian Ocean.
To understand why this is so strange, let’s consider the island of Madagascar for a moment. It is famous for its charismatic animals, including lemurs and color-changing chameleons. The island itself has been isolated for more than 88 million years, and, given its proximity to Africa, it is not surprising that most animals dispersed from the continent to the island. In fact, scientists agree that many of the island’s animals had done so more than 20 million years ago, when a current flowed from Africa straight to the island. The most likely method of travel? Rafts! Piles of floating vegetation cast out to sea during tropical storms, along with their unwitting passengers.
However, starting 20 million years ago, these natural ferries no longer floated from Africa to Madagascar. The reason? Continental drift. Madagascar had drifted too far north, while the northward drift of Australia gave rise to the currents that remain in the Indian Ocean today. These currents, in particular the South Equatorial Current, form an aquatic highway linking the Southeast Asian and Madagascan coasts. The seeds that proliferated to form a major part of today’s Madagascan rain forest got there along this highway.
While we often think of trees shaping the adaptations of animals, the trees in our study are geologically more recent arrivals than many of the animals. This means that the trees likely adapted to the animals, not the other way around. More broadly, our findings also highlight how forests of the world that are separated by thousands of miles can be connected in seemingly implausible ways.
Interested in learning more? The full-length scientific article can be accessed here: www.biomedcentral.com/1471-2148/15/216.
Alex Dornburg is research curator of ichthyology for the North Carolina Museum of Natural Sciences.