Individuals are known to vary extensively in their probability of contacting and spreading parasites (i.e. competence), though the extent to which such variation is the product of host behavior remains enigmatic. We advocate that behavior can be an important determinant of host-parasite dynamics, and describe how realistic characterization of behavioral competence must account for behavioral syndromes in which multiple behaviors interact to influence transmission potential. Here we use a series of studies with Zebra Finches (Taeniopygia guttata) to elucidate the nature of behavioral defenses against vector-borne diseases in songbirds. First, we searched for covariation across multiple axes of anti-vector behavior, and determined whether these behaviors predicted mosquito feeding success. Second, we investigated how the birds’ brains respond to mosquito exposure to identify regions responsible for processing this stimulus, and to ask whether neuronal variation could be responsible for individual differences in behavioral response. Finally, we administered immune challenges to juvenile birds to experimentally test whether developmental plasticity could give rise to adult differences in behavioral competence.
In standardized mosquito feeding trials adult birds with stronger defensive behaviors were less likely to be fed upon. This active mosquito defense appears to represent a distinct axis of behavioral variation, as more generalized anti-vector behaviors (e.g. timing and intensity of activity) were orthogonal and did not predict mosquito feeding success. Following mosquito exposure, birds exhibited increased immediate early gene (IEG) expression in their amygdala, suggesting this brain region is involved in processing mosquito stimuli. However, the lack of an association between amygdala IEG expression and active mosquito defense indicates that other brain regions are responsible for coordinating anti-vector responses. Early-life exposure to a viral simulant (Poly I:C) did not seem to alter the nature or effectiveness of adult mosquito defenses, though more trials are being conducted to fully elucidate whether this or other host behaviors are developmentally plastic. Ultimately, information gained from these studies will improve our understanding of host behavior and its role in zoonotic transmission cycles.