Disease Defense Strategies: Linking Behavior, Immune Function and Disease Ecology in Galapagos Finches and House Finches

Interest in wildlife disease ecology has grown steadily in the past two decades in part due to the recent emergence of numerous diseases of conservation and public health importance. However, two crucial factors---behavioral and immunological heterogeneity---have received little attention. Understanding heterogeneity in behavior and immune function is critical because they determine exposure and susceptibility to disease, respectively. Furthermore, if immunocompetence correlates with behaviors involved in pathogen transmission, then disease dynamics may differ drastically from those predicted by aggregate behavior and immune data alone.;I examine heterogeneities in behavior and immune function in Galapagos finches, which are host to avian pox, an introduced pathogen implicated as a major factor in avian declines and extinctions in Hawaii. I show that pox prevalence has increased dramatically from 2000--2009, but that this increase in prevalence varies by species and human land use type. In both cases, variation in innate immune function at least partially explains variation in susceptibility to pox.;Immune and behavioral defenses against disease are costly and serve a common function; thus organisms may benefit from balancing investment in the two. I propose the "disease defense optimization hypothesis (DDOH)," positing that individuals trade-off investment in behavioral and immunological defenses against pathogen infection. I show that both within and between Galapagos finch species, groups that do not invest in behavioral disease defenses invest more heavily in immune disease defenses, providing initial support for the DDOH. I go on to test the DDOH in captive house finches (Carpodacus mexicanus). In keeping with a basic assumption of the DDOH, male house finches avoid conspecifics displaying sickness behaviors. Furthermore, immune function is inversely related to avoidance of sick social partners, as predicted by the DDOH.;I conclude that, both within and between species, heterogeneities in behavior and immune function exist that have the potential to radically change the dynamics of disease spread in wild populations. Furthermore, the relationship between behavior and immune function is more complex than previously thought and demands further attention to understand the ramifications of individual immunological and behavioral variation for wildlife disease ecology.