Have you ever heard someone say, or thought to yourself, “You are unique”? Of course you have. It’s a pretty common phrase. We’re all snowflakes. Among other sources, our personalities create this variation. No one behaves the same as someone else in all circumstances. Perhaps some individuals will behave similarly in some circumstances, but even then, their behavior would not be exactly the same. Such a statement likely surprises no one, but would it surprise you to hear that snails have personality?
They do! People who study animal behavior often define personality as consistent individual differences in behavior, meaning that individual A behaves in a consistent way that differs from the consistent behavior of individual B. For example, if one were to test the response of individuals to a new object (say, by measuring how close the individual would get to the object), over the course of repeated tests, one individual might consistently get closer to the object than another individual, who consistently stayed farther away. These individuals would be said to have personality.
In a recent study with a marine snail, the common periwinkle (Littorina littorea), and one of its parasites, the authors found that their snails displayed personality, which also varied with infection. Specifically, after removing a snail from the water and poking it, then placing the snail back in the water, the authors timed how long until the snail reemerged from the shell. Interestingly, the authors found that individual snails (each measured three times) differed consistently in how long they remained inside their shell. Snails, furthermore, differed by infection status, with infected snails remaining inside their shells for longer on average than uninfected snails. So all snails had a different and relatively consistent hiding time, but on average, infected snails remained inside their shells for longer periods. Snails are snowflakes too!
But what about those infection results? Did infection change the behavior of snails, or were uninfected snails with certain personalities more likely to acquire infection? Because the study design did not implement controlled infections, testing behavior before and after infection, the authors noted that they could not answer that question. However, either answer would be interesting, and relevant for humans. For example, if personality influences whether an individual acquires infection, then studying such processes in a snail could inform epidemiology of human diseases (studying disease transmission in snails, or the many other non-human animals that have been shown to display personalities, also circumvents the obvious ethical issues with controlled infections in humans). If infection influences personality, then investigating that process in a snail or other animal could likewise inform disease transmission in humans.
Seaman, B. and M. Briffa (2015). Parasites and personality in periwinkles (Littorina littorea): Infection status is associated with mean-level boldness but not repeatability. Behavioural Processes.