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Survival of the Finches
By Wendy Beckman
Ken Petren’s research is for the birds. And the lizards.
But his genetic studies of Charles Darwin’s famed Galápagos finches, not to mention the rowdy social life of South Pacific geckos, are pretty serious stuff.
His research has direct ties to what once was arguably one of the most controversial scientific theories that ever shook up the nonscientific world’s comfortable view of itself. And he could also help us better manage the environment and guarantee the future of the popular darling (at least in TV animation)—of the lizard line.
An associate professor of biological sciences, Petren is using UC’s latest analytical technology to confirm and extend what Darwin observed in 1835 during his visit to the Galápagos Islands, and later developed in his seminal work “On the Origin of Species.”
Petren is also studying the spread (colonization) of geckos—that’s the nocturnal house variety as opposed to a green, day gecko (the Cockney-accented one currently peddling insurance on TV)—in the hope of improving their conservation and management.
The Galápagos archipelago, off the coast of Ecuador, comprises 13 major islands, six smaller islands, and dozens of islets and rocks spread over 23,000 square miles of the eastern Pacific Ocean.
A century after Darwin’s sojourn there, the Ecuadorian government recognized the fragility of this environment and set aside 90 percent of the then-uninhabited area as a national park. They were just in time. Tourism to the Galápagos exploded in the 1960s. Small wonder, when tour guides tout constantly sunny skies, relaxing sea breezes, turquoise-blue ocean and sandy beaches of “crystal white, pink, volcanic black and looking-glass green.”
But with recent increases in both population and tourism, the island species are not as isolated as they once were. This potentially damaging interaction, however, gives researchers another area in which to examine invasive and native species interactions.
Scientists have spent decades seeking evidence to support Darwin’s theory that the Galápagos finches evolved from one species common to the Pacific coast of South America. Within the islands, the finches have adapted to their habitat, especially to different sources of food.
This evolutionary accommodation is reflected in the size and structure of the birds’ bills. For example, vegetarian finches and ground finches have beaks best suited for crushing. Warbler, cactus and woodpecker finches have long, slender bills ideal for probing insects out of crevices.
The woodpecker finch even uses twigs as tools for digging out food deeper than the reach of its beak, and the vampire finch actually pecks at the tail feathers of seabirds to draw blood as a food source.
Ever since joining UC’s faculty in 2000, Petren has been taking teams of faculty and students to the Galápagos Islands to study how various species thrive and evolve. He’s seeking genetic clues as to how one ancestral Galápagos finch evolved into 15 different species. His research team—collaborating with Princeton University Darwin finch specialists Peter and Rosemary Grant and supported by the National Science Foundation—is working to reconstruct the history of populations and species.
Their studies genetically compare tissue from present-day finches with samples taken from museum specimens of birds collected by Darwin himself.
Petren points out, however, that not just anyone can remove tissue samples, which can be as minuscule a slice of one toe pad, from Darwin’s originals.
“You have to make a very strong argument to do destructive testing like this,” he says. “The tissue we take could possibly change the way we perceive and place a value on isolated populations of many other species around the globe.”
Petren and his team bring their samples back for genetic for analysis at the Institute for Genomic Resources, in UC’s environmental health department.
The team’s findings so far show that similarity in finches is unrelated to the proximity of their various islands. Instead it appears to depend on similarities of habitat on their home islands, which can range across the archipelago from low and dry to high and moist.
“People tend to assume most animals move and settle randomly,” Petren explains. “Using the tools of molecular genetics, however, we picked up a signature that suggests they’re selecting where to settle based on habitat, and this is factoring into the formation or divergence of species.”
From Finches to Lizards
To better understand how communities of organisms form, Petren’s lab also studies how house geckos hitchhiked with the original Polynesian and Melanesian islanders, and continue to spread with the help of humans across the Pacific islands.
“We use geckos as a model to understand how invasive species succeed and displace residents,” Petren explains. “Humans are moving geckos around a lot. Some species are residents, having reached the islands thousands of years ago. More recently, however, other species are being introduced by accident with cargo, and sometimes people bring them in for the pet trade.”
Petren says that behavior often determines whether a species can successfully colonize a new habitat and whether it spreads rapidly and affects native species.
He duplicates the geckos’ natural environment as best he can for the 300-plus South Pacific lizards in his lab so he can examine them as they eat, socialize and fight.
Documenting visual displays like tail wags and arches, vocalizations, approaches and retreats, bite-holds, wrestles, licks and copulations—as well as throwing each other off the wall—the researchers found that social interaction between invasive and native species, not just competition for resources or aggression on the invaders’ part, plays a significant role in species turnover.
“Increase in global trade and travel is slowly bringing the world’s biota together,” Petren says, “so we’re bound to lose a great deal of biodiversity in the process. But understanding how species are displaced is the first step in understanding how the process can be managed.”
Reprinted from UC Research, Fall 2006
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