Evol Ecol Res 13: 283-293 (2011) Full PDF if your library subscribes.
Predator presence suppresses immune function in a larval amphibian
Sarah A. Seiter
School of Natural Resources and Environment, University of Michigan, Ann Arbor, Michigan, USA
Correspondence: S.A. Seiter, Department of Biology, The University of North Carolina at Chapel Hill, 337 Wilson Hall, Chapel Hill, NC 27599, USA.
e-mail: sseiter@email.unc.eduABSTRACT
Background: The presence of predators frequently reduces developmental rate in larval amphibians. If physiological and evolutionary trade-offs exist between immunity and predator responses, optimal immune response may not be selected for but the immunological consequences of predator exposure are unknown.
Hypotheses: Amphibian larvae exposed to predators during development will develop more slowly and have weaker immune responses than those reared in a predator-free environment.
Organism: The anuran, Rana sylvatica, reproduces in vernal ponds throughout North America with varying levels of predation. Rana sylvatica tadpoles respond to predators through behavioural and morphological defences resulting in reduced development time.
Site of experiments: The Edwin S. George Biological Reserve, Livingston County, Michigan, March 2007 to July 2007.
Methods: Rana sylvatica tadpoles were randomly assigned to replicate experimental mesocosms. Those with caged insect predators provided the chemical cues of predation. Controls had empty cages. After 6 weeks, tadpoles in each treatment group were given an immune challenge (an injection of the immune elicitor phytohaemagglutinin, a common field test of T-cell mediated immunity). I measured body mass, developmental stage, and immune response (at 24 and 48 h) between experimental and control groups using linear mixed models. I used structural equation modelling (path analysis) to distinguish the direct effects of predator exposure from indirect effects mediated by developmental stage.
Results: Tadpoles reared with predators developed more slowly and had weaker immune responses at both 24 and 48 h compared with controls. Mean immune responses increased with time in both experimental animals and controls. The direct effect of predator exposure contributed more to reduced immune response than did indirect effects mediated by developmental stage.
Keywords: immune responses, indirect effects of predators, inducible defences, larval amphibians, natural enemies, plasticity, Rana sylvatica.
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