FEATURE — Winter 2003
   

 

Exposing Evolutionary Answers
Professor Jonathan Losos (left) and his research team, including doctoral student Jason Kolbe, study species in their natural habitat, so none exist in their lab. However, the lab is not free from denizens; on Losos' arm is Grendel, a prehensile-tailed skink.  

Professor Jonathan Losos and members of his research team study lizards to understand the origins of diversification and how organisms survive.

by Janni Simner

Jonathan Losos has been fascinated by dinosaurs since he was a child. His fascination expanded to include living reptiles after he acquired some pet caimans—close relatives of alligators—the year he was 11, and he's been turning to lizards for glimpses of the past ever since.

As professor of biology in Arts & Sciences at Washington University, Losos uses lizards to integrate questions of ecology and evolution. He seeks to better understand how organisms survive in their present-day environments, how they've changed over time to fit into those environments, and how they're continuing to change. "We can't go back in time," Losos says, "but we can see what happens today." And, if one sees well enough, one can extrapolate back to understand how similar changes have occurred over millions of years.

Losos' primary focus is on the Caribbean-based Anolis lizards. These lizards are particularly well suited to evolutionary studies, being at once tremendously diverse—more than 300 species exist—and fairly isolated, since there's no contact among the lizards on different islands. Yet Losos has found that in spite of this isolation, the lizards on different islands tend to evolve in similar ways.

He and his students conducted a detailed Anolis study in the Greater Antilles; on each island they looked at several species and found each adapted to a particular habitat. One species specialized in living on narrow twigs, for instance; a second confined itself to the lower reaches of tree trunks; a third to ground-level grasses. This in itself was not new; biologists have been observing habitat-specific adaptations since Darwin. What was striking was what Losos observed across the four islands: Not only were the lizards different, but they were different in the same ways. Twig-dwellers tended to be thin and short-legged, for instance (not on one island, but on all). Likewise lower-trunk lizards had long legs and stocky bodies (no matter what island they were on). Yet the similar-looking lizards were clearly very different species; DNA analysis conducted in collaboration with Professor Allan Larson's lab confirmed the fact. (Larson also is a professor in the biology department.)
Anolis valencienni, a twig anole, is found in Jamaica (photo by Jonathan Losos, 1996).

Losos says the study illustrates just how pervasive adaptation and diversification really are. "We see these species competing very strongly for resources," he says, "and that competition leads them to change their use of the habitat to avoid interacting with each other. In miniature form, it's a picture of the great evolutionary events in Earth's history."

The Greater Antilles adaptations were necessarily observed after they had occurred. One of Losos' more recent studies seeks a more direct view. On 12 tiny islands in the Bahamas, he conducted a thorough survey of the existing Anolis populations. Then, taking advantage of the absence of a larger predatory lizard (although these predator populations come and go naturally among these small islands), he introduced the predators to half the sites. Not surprisingly, Losos says, after only a few weeks, "the populations on the islands with the predators are substantially lower in number. But, in turn, the survivors are farther up in the vegetation—and using narrower perches." These survivors still have the long legs they evolved for lower dwellings, however, and they may be having some trouble with their new lodgings. The question is whether their descendants will, as Losos predicts, change over time, developing shorter legs and other characteristics similar to their twig-based counterparts in the Greater Antilles. "We'll monitor them over the next five to 10 to 20 years," he says, "to see if they do in fact adapt to their new circumstances."

Another earlier Bahamas study, conducted with University of California-Davis colleagues Thomas Schoener and David Spiller, provided an unusual chance to observe adaptation under extreme circumstances. The study began by looking at Anolis adaptations that result from competition for resources. Then, in 1996, Hurricane Lili hit the region, dramatically altering the study site.
Anolis grahami, a trunk-crown anole, lives high on the trunk and among branches in Jamaica (photo by Jonathan Losos, 1996).

What might look like a researcher's nightmare was in fact a unique opportunity. Losos, Schoener, and Spiller had just finished a round of data-gathering, and so possessed detailed information on Anolis and other island populations just before the hurricane. By re-examining these populations after the storm, they were able to take a direct look at the effects of such disturbances upon populations.

They found that larger organisms such as lizards are more resistant to such disturbances than smaller ones; that larger population sizes help protect species from moderate disturbances but not from catastrophic ones; and that species that can't move great distances—such as lizards—tend to recover less quickly than those that can.

St. Louis native, Losos decided he wanted pet caimans after seeing an episode of Leave It to Beaver in which Beaver acquired a baby alligator. His mother, Carolyn Losos, A.B. '54 and an Arts & Sciences National Council member, was reluctant to have an alligator—or one of its near relations—in her home, but she deferred the question to Charles Hoessle, a friend of Losos' father. At the time Hoessle was deputy director of the Saint Louis Zoo, and he thought owning caimans was a fine idea; he'd gotten his own start in zoology in a similar way. "So my mom was stuck," Losos says with a laugh. "I got the caimans, and everything else is history."

Losos' teachers in the Ladue (Missouri) School District further encouraged his interest in biology and evolution. So did his undergraduate adviser at Harvard, Ernest Williams, whom Losos describes as the "grand old man of lizard studies." Losos went on to earn his Ph.D. from the University of California-Berkeley, and did postdoctoral work at UC-Davis. He continues to collaborate with his UC-Davis colleagues, Schoener and Spiller.
Professor Losos displays lab mascot, Morton, an Australian-bearded dragon named after Losos' late uncle, alumnus Morton Werner, B.S.B.A. '50.

In 1992 Losos returned to St. Louis and joined Washington University's Department of Biology. "I'm delighted to be back," he says. According to biology department chair Ralph Quatrano, the Spencer T. Olin Professor, the department benefits from both Losos' accomplishments and his enthusiasm. Losos' work has appeared in top publications such as Science, Nature, and Scientific American. Perhaps just as important, Quatrano says, "No matter how busy Jonathan is, if he sees something that's important to do, he'll do it."

This attitude led Losos to his recent role as director of Tyson Research Center (he stepped down in summer 2003), as well as to his current role heading the College of Arts & Sciences' interdisciplinary Environmental Studies Program. Losos is reaching across department lines and working with faculty in biology, anthropology, economics, political science, and other departments to update the program. "I think that's important," Losos says. "I'm very concerned about environmental issues, and it's clear that this is a major issue to our students as well."

Within his own department, Losos enjoys the spirit of collaboration. "The faculty are not only great scientists but also very interactive and friendly people, very collegial," says Losos, who collaborates with Larson, Professor Alan Templeton, and Jon Chase, a new faculty member in biology, on various projects. He intends to work with Peter Morin, the incoming director of Tyson and biology department member.

In Losos' lab, a similar spirit of collegiality prevails. "We get fabulous students at Washington University," Losos says. "I often learn more from them than they do from me."

"It's a great mix of people and ideas," agrees Jason Kolbe, one of Losos' graduate students. Graduate student Luke Harmon adds, "Dr. Losos is really supportive, but he also gives each of us enough space to be creative with our own projects, to become independent scientists."

This fall Losos is teaching the new Freshman Seminar in Environmental Studies, as well as co-teaching an earth and planetary sciences course on dinosaurs, which is cross-listed in environmental studies, for nonmajors. He looks forward to using his childhood fascination to reach a new generation of students. "They think they'll just be learning about cool, big beasts," Losos says, "but we'll also be teaching them about evolution, physiology, and continental drift. They're going to learn a lot about how science operates."

Losos is designing new research studies to examine whether the degree of adaptation observed among Anolis lizards also applies to species in Africa, the southwestern United States, and among isolated populations right near St. Louis. While Losos' prediction is that there will be similar patterns in all these places, he cheerfully admits that he doesn't know for certain what he's going to find. "That's what's so exciting," he says. "We know so much already, yet unexpected findings can still increase our understanding.

"That's great for someone who's curious. It's always exciting to find out what the answers will be."

Janni Simner, A.B. '89, is a free-lance writer based in Tucson, Arizona.