Last Friday, I went on a field trip with botanists John Kress, Dave Erickson and Ida Lopez from the National Museum of Natural History to Plummers Island. Despite being unknown to most outside the circle of Washington area biologists, and maybe the fishermen that frequent its banks on the weekends, the 12-acre island in the Potomac, just nine miles upriver from Washington, D.C., has the distinction of being the most studied island in North America.
The National Park Service, which owns the island, makes this clear on a sign posted on the island’s southeastern tip. This was our point of entry. The water level in the channel between the mainland and the island was looking pretty high, perhaps too high to forge, but some previous visitors had created a log bridge. Up until a few years ago, a boat (marked "Property of the U.S. Government") was tied onshore and the researchers would grab hold of a line strung above the channel and pull themselves across. Apparently, they had problems with people taking joy rides in the boat and mooring it other places, like across the river, so they did away with it.
"Whenever I come out here I feel like I’m in Costa Rica," said Kress, as we followed a trail to a cabin at the highest point in the island maintained by the Biological Society of Washington, the island’s original owners. He stopped along the path to point out the pawpaw, small trees with burgundy flowers (see photo above) and the only species in its family to not be confined to the tropics. "Essentially, we’re standing in a tropical forest," said Kress.
In the past four years, Kress and his colleagues have barcoded all 250 plant species on the island. What this means is that they’ve collected specimen and created a database of a standardized, distinctive segment of DNA from each plant. So, in effect, if they can’t recognize the plant on first sight, or if they spot something similar in another locale, they can analyze its DNA using the database to identify it.
In the past, they’ve needed a plant’s flowers or fruits to classify it, necessitating that they collect samples at a specific time. But with barcoding, they can now use DNA from just about any part of the plant they manage to collect—flowers, fruits, seeds, bark, roots or leaves. While we were on the island, Erickson was actually collecting insects, mostly caterpillars, and the leaves he found them on. He has succeeded in finding plant DNA in the ground up guts of insects, and he hopes to better understand which insects are specialists, meaning they eat certain plant species, and which are generalists, meaning they eat just about anything. Up until now, said Kress, you’d literally have to follow that bug around to find out what it really ate. If researchers collected it off a given plant, they assumed that’s what it fed on, but had no way of telling what else made up its diet. Erickson was bagging specimen right up until we stepped foot off the island. "That’s kind of hard to resist," he said of a plump, fuzzy caterpillar. "What about flies? Do you need flies?" said Lopez, who had an eagle eye for spotting things. But he finally had to say, "I’m done," and b-line it back to the car.
The Consortium for the Barcode of Life (CBOL), headquartered at the National Museum of Natural History, is working to compile a global reference library of DNA barcodes of plants and animals. The goal is to eventually create a handheld barcode devise, similar in concept to those used to scan products in the grocery store, that a botanist or any other person could use to scan and identify a plant in the field. Crazy, huh?
Stay tuned for a story on the work of Kress and his colleagues in the Around the Mall section of the magazine’s August issue.