Seminars on Science
Rob DeSalle



Dr. Rob DeSalle
Dr. Rob DeSalle ©AMNH

Dr. Rob DeSalle, curator in the Museum's Division of Invertebrate Zoology and co-director of its molecular laboratories, has a definite knack for collaboration. Something about him seems to make brilliant people want to work with him. Perhaps it is his casual, open manner; or his boundless curiosity; or his evident enthusiasm and respect for the ideas of others. Perhaps it is his willingness to offer the use of his lab, which contains tremendously expensive machinery that can sequence the DNA of hundreds of organisms in a single day. Or perhaps it is simply the quality of his own research that invites collaboration. At any rate, if you've got an exciting hypothesis about biodiversity and need some DNA sequenced to test it, Rob is your man.

As an undergraduate at the University of Chicago in the 1970s, Rob had vague plans of becoming a social worker. But frequent visits to the Field Museum of Natural History in Chicago eventually inspired him to appear in his advisor's office where he announced that he wanted to study whales. His advisor, a molecular geneticist named James Shapiro, suggested that if Rob really wanted to study whales, he should learn about genetics. Rob took his advice. "My academic career up to then had been very chaotic," Rob says, but he found that the logic and order of genetics provided a structure for his wide-ranging interests. An undergraduate research project at the Field Museum on the genetics of leaf-eared mice left him completely hooked. After earning his B.A., he enrolled in a graduate program at Washington University in St. Louis, and received his Ph.D. in 1984.

One of the first papers Rob read as a graduate student described the sequencing of the first complete genome. Although the genome was that of a virus and not an animal, Rob, like many others, immediately saw the potential of DNA sequencing for studying molecular evolution, which then became his focus. Like many people interested in evolution, Rob studied the Drosophila fruit fly, because it can breed an entire new adult generation every two weeks and its DNA is relatively simple to decode. Rob says the best piece of advice (and the only one he claims to have followed) from his thesis advisor, Alan Templeton, was to choose a research subject that lives in a nice place, "because then you get to go there and collect them." Fortunately for Rob, some of the most fascinating and diverse Drosophila , in terms of color, form, and behavior, live in Hawaii.

The Hawaiian Islands are an especially interesting place to study evolutionary biology because of their unique geological history. As the Pacific continental plate drifts toward Japan, volcanoes periodically erupt at a "hot spot," leaving behind a chain of islands, with the oldest on one end and the newest on the other. What does this mean for biologists? Rob explains: "The age of each species of flies on the islands is different. And they're differentiated in a really nice chronological order."

Though other researchers had studied the effects of the Hawaiian Islands' geological history on the evolution of Drosophila , Rob was among the first to do so using molecular genetics. His research caught the attention of Allan Wilson of the University of California, Berkeley, who is considered by many to be the father of modern molecular evolution. Wilson invited Rob to do a postdoctoral fellowship under him at Berkeley. "Allan wanted to be able to work on these flies with me, because I had a really neat system," Rob says, "and I wanted to go to his lab because he had some great technology. He was on the cutting edge. If I wanted to do something with molecular genetics in his lab, I just had to tell him, and he would set it up for me. It was really great."

Wilson worked closely with Kary Mullis, the inventor of the polymerase chain reaction (PCR) method of sequencing DNA, for which Mullis later won a Nobel Prize. "I actually witnessed PCR being born," Rob recalls. Wilson's students were among the first to use the technique, and Rob remembers seeing people moving tubes from one water bath to the next, by hand, because the process was not yet automated. "It was really kind of funny to watch them," he recalls. "I didn't know what they were doing. But it turns out it was the technique that has revolutionized all of molecular biology."

In the open ocean, the blue shark ( Prionace glauca ) typically feeds on other fishes and squid, although it has been known to attack humans.
Rob, with his two daughters. ©R. DeSalle

Rob continued his research on Drosophila and taught at Yale University from 1986 to 1991, when he accepted a position as assistant curator at the American Museum of Natural History. By joining the Museum staff, Rob had come full circle, because museums had kindled his original interest in genetics.

At the Museum, he continues to study flies, but also uses his expertise in molecular genetics to explore a much wider range of creatures. "Coming to the Museum was a really important move for me," he says. "Here, there were beetles, there were lemurs, there were crustaceans, just all kinds of interesting stuff." With his own team of graduate students and postdocs, he could explore several different questions at once. "It allowed me to say to a student, 'If you need antelope tissue, I know where to get it'"—usually just by walking down the hall and talking to a colleague.

In a university setting, the work of individual researchers often has little in common, and the people just down the hall from Rob might be doing work so unrelated to his that they would have little to talk about. But at the Museum, all the biologists were committed to studying biodiversity, and while one might specialize in spiders and another in leeches, Rob found he had something to talk about with all of them. Best of all, he discovered his new colleagues were very willing to collaborate.

Rob's research began to branch out in exciting new directions, and a few years later, Yale University tried to lure him back. But he decided to continue working at the Museum because of its resources and focus on organismal diversity. "I sincerely believe that if I was at a university, I'd still be studying just Drosophila ," he explains.

One of the most satisfying of his many collaborations was a study with Dr. Howard Rosenbaum of the Wildlife Conservation Society, which allowed him to fulfill his youthful ambition to study whales. During the great whale hunts of the 19th century, one of the most severely depleted species was the right whale. It was easy to catch because it skims the surface while feeding and its body floats after death, making it the "right" whale to hunt. Right whales live in the South Pacific, the North Pacific, and the North Atlantic, and traditionally the northern and southern groups had been considered two different species. Rob, Dr. Rosenbaum, and an international team of cetacean biologists analyzed DNA from animals in each group and found that the two northern groups are genetically different. This means there are actually three species of right whales, not two. Their discovery has important policy implications, because each endangered species needs to be protected individually and a change in species status may afford increased protection.

In addition to their commitment to biodiversity and conservation, the Museum's biology researchers are also united by a common theoretical approach called cladistics. The Museum is considered the birthplace of American cladistics, a system of defining and organizing species by their shared derived traits. In the past, species were discovered and named without an objective, overarching system. But according to cladistics, each branch on the evolutionary tree is defined by a specific trait, or character, that is passed down to all the species in that branch.

Of course, there are different ways to identify these defining hereditary traits. Probably the most useful is an animal's morphology—its shape and structure. But molecular genetics has added a powerful new tool: tracing evolutionary traits through DNA. Neither method is foolproof, because animals can sometimes end up with shared traits without inheriting them from a common ancestor. For instance, two unrelated species can both develop wings (consider a butterfly and a bat), so if you selected wings as the shared trait that indicated a common ancestor, you could be misled. This type of shared trait is called "convergence."

Genetic patterns are susceptible to the problem of convergence, too. They are also full of meaningless data that Rob calls "noise." But while other scientists debate the relative merits of morphology versus molecular data, Rob believes that, "Instead of opposing morphology with molecules, we should be putting them together, and letting the two different kinds of data tell us what our patterns are."

In the open ocean, the blue shark ( Prionace glauca ) typically feeds on other fishes and squid, although it has been known to attack humans.
Dr. DeSalle takes a moment away from his research in the American Museum of Natural History Molecular Lab. ©AMNH

An example of this approach is a series of studies Rob did with curator David Grimaldi, one of Rob's first collaborators at the Museum. "He's a morphologist, and a wonderful artist—draws his flies like no one else can draw flies," Rob says admiringly. The two examined the same species of Drosophila flies—Grimaldi studying their morphology, and Rob looking at their DNA—and obtained conflicting results. "In essence, it turns out that neither of us had enough data," Rob says. "And the combination of the two data sets actually gave us a much more reasonable hypothesis."

Most of the time, the molecules and morphology agree, but when they don't, Rob says, the results can be startling. "One of my students, John Gatesy, who's at the University of California, Irvine, now, has looked at the relationship between hippopotamuses and whales. We can show really clearly with molecular data that they are sister taxa, which means they are close relatives," Rob explains.

Needless to say, this was a big surprise. Few would guess that whales and hippos are related by looking at them—that is, by their morphology. But in this case, Rob says, "the sequence data are overwhelming the morphological data." So researchers must now consider how these creatures might have descended from a common ancestor, a question that most likely would never have arisen without having looked at their DNA.

" It's just a really great time to be in science," says Rob. "I bet you every scientist in every age thinks that, but this is truly a neat time. The capabilities for us to gather data for almost any question at the genetic level are there." Being a Museum curator allows him to explore as many of these questions as he wants, which makes it the perfect job for Rob.
In addition to the stimulating environment and wealth of potential collaborators, the Museum also gives Rob the opportunity to help design exhibition spaces, such as "The Genomic Revolution" and "Epidemic!". "The Genomic Revolution" explored the science and technology of genomics research as well as the ethical, social, and legal implications of this research. "Epidemic!" explored infectious disease. Rob also helps create magazines for children, books of essays, and content for the children's website, Ology—and of course, online science courses for teachers, such as this one. But his primary focus is on his research. As one of over 40 curators at the Museum, Rob works on exhibitions and educational programs, while he continues to explore the many unanswered questions that make his scientific career an endlessly rewarding and fascinating pursuit.

print version email this