Volume 1, Issue 3
The Tale of the Otter and the Abalone
When David Lindberg, chair of UC Berkeley's Department of Integrative Biology, was a graduate student more than twenty years ago, he was faced with a conundrum off the coast of California. Lindberg was assisting UC Santa Cruz marine ecologist Jim Estes in a protective effort to move a population of endangered sea otters from central to southern California. While the relocation was deemed necessary, conservationists also worried that the otters might destroy the rich shellfish population already living there, particularly the large abalone so familiar to seafood connoisseurs in the western United States and Japan. The concern seemed valid, but raised an evolutionary riddle.
David R. Lindberg was formerly the director of UC Berkeley's Museum of Paleontology. He's currently a curator there. (courtesy Howard Hughes Medical Institute)
"If you look at the fossil record, big abalone appear around the same time as otters in California," Lindberg says. "So if otters are a horrible predator that just bash the abalone, why did the abalone evolve to a size so big that they couldn't fit back in the rocks where they'd be protected?"
Now, Lindberg, Estes, and Charles Wray of Mount Desert Island Biological Laboratory, may have solved the mystery. The story they uncovered is a quintessential example of how modern-day integrative biology is a melting pot of molecular genetics, paleontology, and good old-fashioned natural history.
Most of the world's abalone live in tropical coral reefs and reach no more than 50mm in length, far smaller than the Northern Pacific's salad bowl-sized species. This led the researchers to hypothesize that the Northern Pacific abalone get big by eating well, specifically the high-quality algae in the cold waters. To test their hypothesis, Lindberg and his colleagues went back 40 million years.
"When you do historical studies, you can't run controlled experiments," says Lindberg, also a curator at the UC Berkeley Museum of Paleontology. "But you can look at the distant past, make predictions about the more recent past, and test your hypothesis that way. So we set out to map the abalone's size increase through time."
During the early Cenozoic era, when the configuration of earth's continents was very different than today, the forming of the Antarctic Ice Sheet allowed some abalone to dive into Australia and South America. With the cooler temperatures came an abundance of fleshy macroalgae for the abalone to feast upon leading to their first increase in size. Over millennia, the abalone followed the high-energy food, spreading eastward and north along the south Pacific basin.
During the course of their research, the scientists ran genetic tests on tissue samples for dozens of abalone species from around the world. The results showed that the large animals were all related, having completed their radiation from South to North America before the Isthmus of Panama rose from the sea three million years ago.
Placing one abalone shell inside another reveals how the 40 mm tropical species Haliotis glabra is dwarfed by the cold water Pacific species Haliotis rufescens. (courtesy the researchers)
"That's when their size absolutely explodes," Lindberg says. "But these north Pacific abalone are not grazers. They feed on the drift of the high-quality kelp."
And therein lies the secret to the large abalone's survival among the otters. The abalone hide in the cracks and crevices of the shallow reefs and essentially order in their dinner. Or they make their homes in the surf zone, hiding underneath the sides of boulders while waiting for the kelp to accumulate.
"When you piece together the natural history with the fossil record and the molecular phylogeny, the entire pattern makes perfect evolutionary sense," Lindberg says.
Still, there was one thing that continued to trouble Lindberg. There was no evidence that any abalone had ever lived in South America along the Chilean coast.
"That was a problem because if you look at the phylogeny and track the position of the continents, the abalone should have been there during their radiation toward the eastern North Pacific Ocean," he says.
Fortunately, Lindberg stumbled across scientific papers describing how El Niño periodically wipes out the algae and kelp beds on the Chilean coast. Armed with that information, Lindberg became convinced that abalone had in fact established populations in the area but that El Niño wiped out their food source, leading to their extinction after perhaps a few thousand years. That limited lifetime combined with the constant uplift of the tectonic plates in the region, Lindberg says, would mean that intact fossilized abalone would be few and far between.
Still, Lindberg says, "I have no doubt that at some point someone will pull an abalone out of the Chilean fossil record."
And when that day comes, Lindberg's evolutionary puzzle of the Abalone will be complete. For the time being, anyway.