New threats, new science
by Eric Sorensen | © Washington State University
Sure, Darwin had to battle seasickness aboard the HMS Beagle, and he spent nearly five years getting to and from the Galapagos Islands, and it took another 23 years to incorporate his findings into his seminal work on evolutionary biology.
But at least he lived in a slow-motion world of ship travel and isolated, slowly evolving species. Today, a scientist, or an exotic parasite for that matter, can get from London to the Galapagos in 24 hours. The parasite can start changing the biology of a place almost overnight. The scientist will have trouble keeping up.
Jeb Owen has seen as much, not by visiting the Galapagos, but by peering into drops of blood drawn from the species of finches that Darwin studied more than 150 years ago. Darwin saw how the birds’ beaks had slowly changed, supporting his view that they diversified, or evolved, into different species from a common ancestor. Owen has seen how the birds are responding to two introduced parasites, which are dramatically challenging the biological hand of cards they were originally dealt.
Through this and other projects, the assistant professor of entomology is helping pioneer the brave new world of ecological immunology. It’s a shift, he says, from traditional ecological thinking that concentrates on animals’ growth rates, size, territory, habitat, and predator-prey relationships—nature red in tooth and claw. Ecological immunology concentrates more on the deft, fleet-footed challenges posed by some of biology’s greatest survivors—parasites and pathogens.
The rise of the field highlights a growing interest in the roles of pathogens in shaping the ecology and evolution of a species, says Owen.
“It’s not just what’s going to eat you,” he says. “It’s what’s going to make you sick. And more importantly—which is part of what this field of research is about—why are you going to get sick?”
In a way, ecological immunologists are following moving targets, plotting the shifting dynamics between predators and prey, or hosts and parasites. This concept was first raised in the early ’70s by University of Chicago biologist Leigh Van Valen, who said a species survives best by quickly responding to the adaptations of its adversary. Van Valen, who died in October, called this the “Red Queen Hypothesis,” after the Through the Looking-Glass character who says to Alice: “Now, here, you see, it takes all the running you can do to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that.”
It’s an arms race, and ecological immunologists are trying to figure out who is gaining on whom. Moreover, says Owen, are there other factors that will shape that arms race?
One way ecological immunologists get at that question is by testing the immune systems of varying creatures. At first glance, one would think that those with strong immune systems would be favored by natural selection, surviving better than other individuals and passing on this trait to their offspring.
But Owen and other researchers find that there is a lot of variation among individuals and that their susceptibility to infection varies a lot, too. This is likely because an animal has a lot to do besides fight off infection, like get food and rear young. Animal life is a constant high-stakes calculus in which everything has a cost, and sometimes an organism has other, more pressing needs, like an overworked human saying, “I can’t afford to get sick right now.” Growing and reproducing can take precedence; they can in turn affect immune function.
“And so we want to know how that works, in part because we want to know what’s shaping the immune system,” says Owen. “But also we really want to know, what governs the occurrence of infectious disease?”
Last year, Owen and colleagues at the University of Utah published a study in the journal PLoS ONE describing how Darwin finches are responding to two exotic parasites, a virus and a nest fly. As far as they know, the study was the first to show wild birds developing a specific antibody response to multiple parasites.
The question now is what price the birds are paying to fight off the invaders. Such questions will be even more important in coming years as invaders travel the world. Lending an even newer wrinkle to the field is the effect of global warming, which can expand the range of insect-borne diseases traditionally confined to the tropics and sub-tropics.
Because global warming is destabilizing, says Owen, “we’re starting to see animals more frequently stressed. Their food availability, their refuges, are fragmented and are less consistent. And we’ve observed that when animal populations get physiologically stressed, they become more susceptible to disease.”
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