When individual animals show consistent behavioral responses in different scenarios or in similar scenarios across time, and individuals vary in their responses, we can say that there are behavioral ‘types’ or personalities in that animal population. For instance, some animals might have aggressive personalities, where those individuals are consistently more aggressive than other individuals in the population. Personality is getting a lot of attention in disease ecology right now because particular animal behavioral traits (or suites of personality traits = behavioral syndromes) might increase an individual’s risk of becoming infected by a pathogen or the probability that an infected individual transmits a pathogen. For instance, I recently blogged about how Tasmanian devils that receive many head wounds in aggressive encounters (=lower social rank individuals) are less likely to become infected by Tasmanian devil facial tumor disease than individuals with fewer head wounds (=more aggressive/higher social rank individuals).
In a recent study, Seaman and Briffa (2015) set out to determine (1) whether snails have personalities and (2) whether snail personality traits are related to trematode infection status. The personality trait that they considered was “re-opening” time, which was a measure of how reluctant the snail was to re-open it’s operculum after being poked by the investigator. I’m not ashamed to say that this reads like an excerpt from the description of my dream job: “All observations were carried out by a single observer who had practised touching snail’s feet with a consistent level of pressure.”
Seaman and Briffa (2015) found that snails did have consistent responses to the mock predation encounters, where individual snails took consistently more or less time than average to re-open their operculum. Additionally, snails that were first intermediate hosts for trematodes (i.e., castrated snails) had longer re-open times, on average.
Because Seaman and Briffa (2015) used uninfected and infected field snails – as opposed to experimentally infecting their snails – it is unclear whether the differences in snail opening times is driven by infection, or whether the differences in opening times somehow affects the probability of becoming infected. Even if infection is driving the different mean response times, it doesn’t mean that the parasites are manipulating the snails. For instance, it might just be that infected snails are showing a sickness response, which makes them act sluggish. (Heh, get it?) Or it could be that the trematodes are manipulating the snails to make them behave more cautiously, thereby decreasing the probability that the host (and parasites!) gets eaten by a predator.
Because there are multiple potential mechanisms at work, I couldn’t decide on the dialogue of this cartoon. So, pick your favorite!
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.