Some species have been incredibly adept at expanding their ranges. We are investigating what behavioral and physiological adjustments facilitate invasions in one of the most broadly distributed avian invaders, the house sparrow. Collaborators from all over the world (HOSPnet) are helping us characterize the endocrine and immune systems of native and introduced populations, particularly in the ongoing colonizations of Kenya and Senegal, where invasions began in just the last ~60 years. With past support from the National Science foundation, we discovered important roles for the glucocorticoid, corticosterone, and regulation of innate immune functions. Recently, we've begun investigating molecular epigenetic variation among individuals and populations, finding a role for DNA methylation in promoters as impactful of phenotypic variation and colonization of new areas.
Stressors are thought of as immunosuppressive, but in some situations, immune defenses may be adjusted by these hormones to protect animals from infections after failed predation events or aggressive interactions. With support from NSF, we and the Unnasch lab are studying the role of the stress hormone, corticosterone, as a driver of individual host variation in competence for West Nile virus (WNV). We have found that this hormone influences the attractiveness of hosts to vectors as well as host competence for transmission. We've recently expanded our work into investigations of light pollution impacts on host competence, finding that dim light at night extends the infectious period of a common host of WNV, the house sparrow.
Body size affects almost all biological traits, but its influences on defenses, and especially immune systems, are largely unknown. This absence of information is surprising becuase large and small hosts likely experience quite different risks of parasite exposure and quite different consequences of infection. With recent funding from the National Science Foundation, colleagues and we are asking how body size impacts the organization of innate immune defenses among terrestrial mammals spanning 7 orders of magnitude body size. We have already found that the circulating neutrophil is much larger than would be expected from isometry. Figure courtesy of Kirk Klasing based on an ongoing project.