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Summary: Density-dependent competition and selection on
immune function in genetic lizard morphs
Erik Svensson*, Barry Sinervo, and Tosha Comendant
Department of Ecology and Evolutionary Biology, Earth and Marine Sciences Building, University of California, Santa Cruz, CA 95064
Edited by Mary Jane West-Eberhard, Smithsonian Tropical Research Institute, Ciudad Universitaria, Costa Rica, and approved August 21, 2001 (received for
review February 12, 2001)
Density-dependent territorial interactions have been suggested to
cause immunosuppression and thereby decrease fitness, but em-
pirical support from natural populations is lacking. Data from a
natural lizard population (Uta stansburiana) showed that breeding
females surrounded by many territorial neighbors had suppressed
immune function. Furthermore, variation in immunological condi-
tion had different effects on the fitness of the two heritable female
throat-color morphs in this population. These interactive fitness
effects caused correlational selection between female throat color
and immune responsiveness. Population genetic theory predicts
that this should have lead to the buildup and preservation of a
genetic correlation between female morphotype and immunolog-
ical condition. Accordingly, the throat color of a female was
genetically correlated (rA 1.36; SE 0.55) with her daughter's
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