What's the News: Infections that change an organism's personality are a strange little corner of biology, with toxoplasmosis
, which brainwashes mice and rats to have no fear of cats, topping the list. But scientists think that more pedestrian infections could play a role in shaping personality, especially when they happen early in life. Ducklings provide the latest data that this theory may have something to it. How the Heck:
Ducks assess an object's color when deciding whether it's safe, showing a noted preference for green and a dislike of orange, which researchers think might indicate that insects of that color can be toxic.
To see whether they could get ducks to branch out, as well as be more active in unfamiliar environments, they first simulated a parasite infection by injecting ducklings at various stages of development with sheep red blood cells, which challenge the immune system in a similar way. (They didn't infect them with real parasites because they wanted the same level of immune reaction in each duck, and it would require a much larger sample size to average out the varying effects that pathogens have on different individuals.)
Once those ducklings and their uninjected counterparts grew up, the team had them waddle into an unfamiliar test arena equipped with four objects of different colors. They tracked the ducks' interactions with the objects, and then exposed them to similar objects in the same room later, when it had become familiar.
They found that ducks whose immune systems had been challenged in the middle of their development were more apt to approach orange objects than the others, while all ducks whose immune systems had been challenged were more adventurous in the unfamiliar space. It's possible that infections during development make ducks more apt to roam and take risks in an effort to recoup the energy lost in battling a pathogen or to get away from the pathogen-contaminated area, the researchers think.
What's the Context:
The most well-known link between personality and infection involves toxoplasmosis, which is caused by the
protozoan. The parasite lives mainly in cats, but it also spends part of its life cycle in animals like mice and rats, where it causes a strange shift in behavior: the rodents are no longer afraid of cats, and may even seek out cat urine. The result, of course, is that the cat dines on the new carriers of the protozoan, and the pathogen continues its life cycle.
Lyme disease also seems to trigger behavioral changes in a small percentage of people, who become noticeably more aggressive.
But as scientists have realized that personality is governed by both genetic and environmental factors, they have begun to investigate the idea that permanent changes in personality could result from events that happen during development. Such changes could help individuals adapt to their environments---for instance, by migrating away from a polluted area or seeking new sources of food when familiar sources are scarce.
Reference: Ontogenetic immune challenges shape adult personality in mallard ducks. Michael W. Butler, Matthew B. Toomey, Kevin J. McGraw and Melissah Rowe. Proc. R. Soc. B published online 8 June 2011. doi: 10.1098/rspb.2011.0842
Image credit: Michael Butler, ASU