Condition, genotype-by-environment interaction, and correlational selection in lizard life-history morphs

We compared reproductive allocation and variation in condition and survivor ship of two heritable female throat color morphs (orange and yellow) in a f ree-living population of side-blotched lizards (Uta stansburiana). Using pa th analysis and structural equation modeling, we investigated how variation in the social environment affected clutch size and egg mass and two condit ion traits (postlaying mass, immunological condition) and how these traits in turn affected female field survival. In the presence of many neighbors, both morphs increased their clutch sizes, although these effects were only significant in yellow females. In addition, yellow females increased their egg mass in the presence of many orange neighbors. Orange females surrounde d by many orange neighbors showed sign of stress in the form of immunosuppr ession, whereas this effect was less pronounced in yellow females. The morp hs also differed in the impact of variation in clutch size and egg mass on both condition traits. Finally, female morphotype and immune responsiveness affected fitness interactively, and hence these two traits showed signs of fitness epistasis: Selection gradients on this trait were opposite in sign in the two morphs. The correlational selection gradient (gamma (throatxant ibody) (response)) between female throat color and antibody responsiveness was -0.365. Our data thus reveal important interactive effects such as geno type-by-environment interaction toward the social environment and morph-spe cific trade-offs as well as the occurrence of correlational selection. We d iscuss the use of naturally occurring and conspicuous genetic polymorphisms in field studies of selection and life-history allocation.