Repeatability of cell-mediated and innate immunity, and other fitness-related traits, in the Grey Partridge

Immunocompetence is considered a reliable indicator of general body condition and ultimately of fitness. It has been suggested that, as a parameter subjected to intense directional selection, the level of additive genetic variance expressed should be reduced; on the other hand, theoretical models of host-parasite coevolution assume that variation in parasite resistance has a genetic basis. Contradictory results have been reported in birds, since the heritability of immune responses varies from nil to high. In this study of Grey Partridge (Perdix perdix (L., 1758)), we examined the heritability of immune condition (PHA reaction, an index of T-cell-mediated immunocompetence) and of some parameters traditionally considered important for chick survival, such as egg mass and chick growth. Two statistical approaches were used: parent-offspring regression and full-sibling intra-clutch repeatability. The repeatability of other parameters that reflect egg quality (egg proteins, lipids, and carotenoids) and of substances that confer innate immunity (lysozyme and avidin) was also investigated. In agreement with previous studies, we found nonsignificant heritability for cell-mediated immunocompetence. In contrast, there were significant repeatabilities of chick mass and several egg characteristics (mass, size, total proteins), while lipid and carotenoid concentrations were not repeatable. For the first time in birds, we found significant repeatability of two molecules, lysozyme and avidin, that confer innate immunity to the developing embryo.