Evolutionary Biology, Genetics
University of Texas at Austin
Dr. Bolnick is also an associate professor of integrative biology at the University of Texas at Austin and an adjunct associate professor of microbiology and immunology at the University of Texas Medical Branch at Galveston.
Dan Bolnick is studying the ecological basis for geographic variation in parasite abundance, and how the immune system evolves in response to this geographic variation. He is using an emerging model organism, the threespine stickleback (Gasterosteus aculeatus), for this research.
Growing up, Daniel Bolnick lived the dream of every adventurous child. The son of a development economist who worked and lived in such exotic locales as Indonesia and Zambia, Bolnick spent more time soaking up nature than books.
"As early as high school, I was spending time hobnobbing with field biologists," Bolnick recalls of the time when he crisscrossed central Africa in search of birds. "One of the founding experiences of my life was spending a lot of time outdoors. It sparked an interest in natural history and biological diversity."
Today, Bolnick is an evolutionary biologist at the University of Texas at Austin. And the romance of working in the outdoors still exerts a defining influence, providing the setting for his seminal studies of natural selection, speciation (the biological processes that lead to new species), and the coevolution of animals and their parasites. His work, beginning in graduate school with a single-author paper in Nature, has helped explain the dynamics of how animals expand their environmental niches and form new species within a specific geographic area.
For the past decade, Bolnick has spent his summers on British Columbia's Vancouver Island, hopping from lake to stream to marine estuary to explore the evolutionary dynamics of the threespine stickleback, a small fish that inhabits temperate marine and freshwater environments.
Vancouver Island, Bolnick explains, is an ideal laboratory for his research because 12,000 years ago retreating glaciers left a blank canvas of lifeless lakes and streams — environments that were eventually colonized by animals, including the stickleback's marine ancestor. "The fish got there by colonizing from the ocean. Every watershed, every river system, every lake represents a replicate of an unparalleled evolutionary experiment."
The environments colonized by the sticklebacks vary in size and in the productivity and makeup of their ecosystems, including predator, prey, and parasite dynamics. As the fish adapted to their new habitats, natural selection prompted a diverse array of traits and characteristics — size, shape, color, ability to cope with specific parasites and predators — that make the sticklebacks of Vancouver Island a powerful model of the driving forces of evolution.
"I can identify on sight which lake or stream a fish comes from," notes Bolnick. "There is very striking variation and that is something we can use to ask: What in their environments caused these populations to differ from each other? What genetic changes were necessary to evolve those differences?"
Bolnick also wants to know how the fish coevolved with other organisms. Each lake, he says, harbors a distinctive community of parasites. "In the course of our studies, we stumbled across an interesting story," Bolnick explains. "From lake to lake, not only did the fish differ, but the other species they were interacting with were different. We can sample one lake and never see a tapeworm. On the other hand, if I drive five minutes to another lake, about 80 percent of the fish will have tapeworms."
Knowing that the parasite populations differ dramatically in terms of type and density, says Bolnick, provides an opportunity to test whether the stickleback's exposure to different parasites in different settings prompts genetic changes in the fish's immune system. For example, if a stickleback from a lake that lacks tapeworms is put in another lake whose dominant parasite is a tapeworm, how will that stickleback fare compared with one that ordinarily lives in the lake? And for those sticklebacks that ordinarily live in the tapeworm-filled second lake, "What is it in their genome that is changing that allows them to adapt to their parasites, or maybe makes them more vulnerable?"
To help identify those changes, Bolnick plans to relocate sticklebacks between sites to see if the coevolution of a fish population and its parasites confers what he calls "a home field advantage."
Insights about the interplay of host, parasite, and geographic variation not only help explain the mechanics of diversity, Bolnick says, but also may improve the understanding of chronic parasite-borne diseases that affect humans, such as malaria and dengue fever. "In Africa, you can be in a hot spot for high incidences of malaria, but if you travel 20 miles [to a higher, cooler elevation] you can be out of that hot spot completely." Bolnick believes that the Vancouver Island sticklebacks and their parasites can help reveal how the spatial structure of a landscapeits geology, habitats, and climateinfluences evolution. "We can come up with a picture in which spatial structure of the environment either inhibits or facilitates adaptation to a parasite."
The decade of work Bolnick has invested in canvassing the evolutionary biology of Vancouver Island's sticklebacks and their parasites, and his planned efforts to plumb the genetic basis of their interrelationships, will help give science a new tack on ecological variation. Gaining that insight in a laboratory composed of the 50 or so lakes that pock Vancouver Island, says Bolnick, is the perfect fit for a biologist first inspired by the diversity he observed as a teenager in the African and Indonesian bush.