COS 220-4 - How does infection affect within- and between-individual variation in host behavior?

Background/Question/Methods

The behavior of infected hosts is vitally important for both their fitness and that of their parasites through effects on transmission. However, the factors affecting infected host behavior are poorly understood. In particular, it is unclear whether individual host behavior changes as infection progresses, or as a function of the number of parasites infecting that individual (‘infection intensity’). Research has focused on the effect of variation in intensity between hosts, but intensity can also vary dramatically over the course of an individual host’s infection. We conducted behavioral trials to quantify the activity of Trinidadian guppies (Poecilia reticulata) infected with the monogenean parasite Gyrodactylus turnbulli over the course of infection. We recorded individual guppy behavior three times a day over the course of 4 separate days encompassing pre, early, peak, and late infection periods. We then used linear mixed models to determine the proportion of variation explained by individual behavior over the different time periods of infection.

Results/Conclusions

We found that the activity level of male guppies decreased with increased rate of parasite growth prior to the behavior trial, while females’ activity increased with parasite growth rate. Further, we found that a large portion of variation was explained by the individual, that is guppies showed repeatable individual variation in activity level, but host behavior also varied across infection duration. These findings suggest that even though parasite infection affects host behavior, there is still a lot of consistent individual variation between hosts. We, therefore, found that parasite infection can change host behavior, but that these changes are variable between hosts and not consistent across the infection duration. Further study should focus on other potential factors affecting infected host behavior in a predictable way to aid in the identification of highly competent individuals.