Density-dependent competition and selection on immune function in genetic lizard morphs

Density-dependent territorial interactions have been suggested to cause imm unosuppression and thereby decrease fitness, but empirical support from nat ural populations is lacking. Data from a natural lizard population (Uta sta nsburiana) showed that breeding females surrounded by many territorial neig hbors had suppressed immune function. Furthermore, variation in immunologic al condition had different effects on the fitness of the two heritable fema le throat-color morphs in this population. These interactive fitness effect s caused correlational selection between female throat color and immune res ponsiveness. Population genetic theory predicts that this should have lead to the buildup and preservation of a genetic correlation between female mor photype and immunological condition. Accordingly, the throat color of a fem ale was genetically correlated (r(A) = -1.36; SE = 0.55) with her daughter' s immune responsiveness.