109.2 Saturday, Jan. 7 Infection and cold stress result in additive energetic costs and altered host immunity in a naturally occurring host-pathogen system. DURANT, S.E.*; HAWLEY, D.M.; ADELMAN, J.S.; WILSON, A.F; HOPKINS, W.A.; Virginia Tech; Virginia Tech; Virginia Tech; Princeton Univ; Virginia Tech email@example.com
The role of abiotic factors such as temperature in mediating host susceptibility to pathogens is of growing interest in disease ecology. For endotherms, thermoregulation and resistance to pathogens are two energetically demanding processes that can co-occur during seasonal pathogen epidemics. In house finches (Carpodacus mexicanus) outbreaks of Mycoplasma gallisepticum occur in months when ambient temperatures are often below thermoneutral (TN). Here we examined whether ambient temperature mediates host susceptibility to M. gallisepticum by experimentally infecting wild-caught house finches at either TN or sub-thermoneutral (STN) ambient temperatures. We simultaneously quantified the resting metabolic costs of infection, measures of body condition, disease expression, immune responses, and pathogen loads at both ambient temperatures. The simultaneous, additive demands of thermoregulating and combating infection resulted in an average 42.2% increase in resting metabolic rate resulting in an additional nightime energy requirement of 4.68kJ per day compared to uninfected birds at TN, a value higher than the daily energetic cost of feather molt in passerines. Energetic costs of infection were equivalent at both ambient temperatures. House finches at STN temperatures had significantly lower disease expression and higher circulating levels of the cytokine interleukin-6 in response to experimental infection with M. gallisepticum than finches at TN, yet pathogen loads did not differ between the two ambient temperature treatments. To our knowledge, this is among the first studies to estimate the energetic cost of an acute infection with a naturally occurring, infectious wildlife pathogen in an ecologically relevant host.