Volume 5, Issue 37 May 2008
The Living Story of Sulawesi
Jim McGuire during the nighttime capture of a reticulated python in Central Sulawesi, Indonesia. He is a professor of integrated biology and curator of herpetology at the university's Museum of Vertebrate Zoology. Photo credit: Ben Evans
The Indonesian island of Sulawesi is a 12,000-square-mile jigsaw puzzle. During the past 25 million years, drifting tectonic plates tore four separate paleo-islands from the far corners of the South Pacific and smashed them together in a steamy corner of Southeast Asia.
This turbulent history has turned Sulawesi into a complex biological cipher. Today, it houses a mélange of species with confusing origins: some may have been passengers on the original islands, some may have arrived afterward, and some may have evolved from the mix.
McGuire collects snakes, lizards and frogs throughout Sulawesi in areas such as Bogani Nani Wartabone National Park. Photo credit: Jim McGuire
Jim McGuire, curator of herpetology at Berkeley's Museum of Vertebrate Zoology and a professor of integrative biology, is studying how these species evolved and came to be distributed on Sulawesi today. McGuire first visited Sulawesi while collecting flying lizards of the genus Draco. When he sat down to analyze specimens collected from across the island's four peninsulas, he was astonished by what he found. Based on body shape, the reptiles could be sorted into three morphologically distinct species. But the genes carried by their mitochondria, the powerhouses of cells, told a different story. This data suggested that the three groups could be comprised of multiple "cryptic" species identical to the naked eye but apparently unable to interbreed.
"It was as if they were cut off from each other at some point. But in many cases we don't know what the underlying mechanism would be," McGuire says. The story becomes even more complicated when species from neighboring islands are considered. Many of the "cryptic" Sulawesi species have given rise to new species on off-shore islands. As a consequence, they are more closely related to anatomically distinct lizards now living on other islands rather than to their apparently identical next-door neighbors on Sulawesi.
Flying lizards such as Draco beccarii are one of McGuire's primary interests. These tropical lizards can glide through the air with remarkable accuracy by expanding their ribs into a patagium, or wing. Photo credit: Jim McGuire
Then McGuire read about Sulawesi's macaque monkeys, which comprise seven distinct species. The ranges of many meet at the same localities where the genetically distinct but morphologically identical flying lizards meet.
These findings inspired McGuire to compare the genetics of nine different types of Sulawesi fauna and analyze their origins. His goal is to piece together the story of when each animal group arrived on the islands and how they have fragmented to produce today's range of species.
A Draco beccarii male clinging to a tree. Photo credit: Jim McGuire
It's hard to imagine a more challenging problem. "It is the most difficult place in the world, I think, to do this sort of biogeographical analysis because the tectonic history has been so complex," he says.
Nearly every year since 2004, McGuire has visited the island for months at a time, hacking through thick foliage and traveling bone-rattling jungle roads to collect lizards, frogs, and other island species. Along the way, he has collected in areas few scientists have visited before.
While collecting, McGuire roughs it in field camps such as this one in Gunung Karua, Central Sulawesi, as his home base. Photo credit: Jim McGuire
"On every one of these trips, we find all sorts of new species that haven't been documented before. And a lot of those species are in primary forest habitats," he says. "I feel that I have a moral obligation to explore and document this species diversity before we wipe it all out."
Back at Berkeley, McGuire compares the species' mitochondrial and nuclear DNA, which evolve at different rates. With this approach, called coalescent-based population genetic analysis, he can determine whether the animals are still genetically isolated or whether genetic differences detected in the mitochondrial DNA are merely artifacts of a previous period of isolation.
An animated movie of the formation of Southeast Asia based on tectonic plate movements. Sulawesi is located at the intersection of the central latitude and longitude lines.
Based on these data, he uses computer simulations to reconstruct the evolutionary history of these animal groups. He then plans to go back and study contact zones between species more closely to try to identify any environmental or ecological barriers, such as past flooding or the presence of a predator, that are enforcing species isolation.
"Once we've completed this, I think we could have a better understanding of biogeography in Sulawesi than virtually anywhere else in the world," McGuire says.