Negative effects of changing temperature on amphibian immunity under field conditions

1. Recent evidence of the important role of emerging diseases in amphibian population declines makes it increasingly important to understand how environmental changes affect amphibian immune systems. 2. Temperature-dependent immunity may be particularly important to amphibian disease dynamics, especially in temperate regions. Changes in temperature are expected to cause deviations away from optimal levels of immunity until the immune system can respond. 3. To test whether temperature changes cause deviations from optimal immunity under natural conditions, we conducted a seasonal survey of adult Red-Spotted Newts and measured basal levels of several immunological variables. 4. We then examined these findings in relation to: (1) the lag hypothesis, which predicts that changes in temperature-dependent immune parameters lag behind short-term temperature changes, and (2) the seasonal acclimation hypothesis, which predicts that immune cell production declines during long-term temperature decreases until amphibians can fully acclimate to winter conditions. 5. Our results supported both hypotheses, showing a spring lag effect on lymphocyte levels and an even stronger seasonal acclimation effect on lymphocytes, neutrophils and eosinophils in the autumn. Our findings suggest that temperature variability causes increased susceptibility of amphibians to infection, and they have implications for the emergence of disease and the potential for climate change to exacerbate amphibian decline.