Early-life stress has sex-specific effects on immune function in adult song sparrows.

Multiple components of the immune system are modulated by environmental factors, including exposure to stressors. In particular, chronic stressors can impair development of the immune system, leading to alterations in immune function in adulthood. While these effects have been well established in mammals, less is known about how developmental stress modulates immunity in nonmammalian species. We determined the long-term effects of exposure to early-life stressors on immunity in song sparrows including the swelling response to phytohemagglutinin (PHA) and several measures of constitutive innate immunity. Song sparrows were reared in captivity from 3 d of age and exposed to control conditions, food restriction, or corticosterone (CORT) treatment. Males exposed to food restriction or CORT treatment had less swelling of the wing web in response to PHA than control males; however, neither treatment affected the swelling response to PHA in females. The treatments also had sex-specific effects on constitutive innate immune function. Specifically, CORT-treated males had lower antimicrobial capacity toward a strain of the bacterium E. coli but higher antimicrobial activity toward a strain of the fungus Candida albicans compared to food-restricted or control males. In contrast, neither treatment affected constitutive innate immunity in females. These results suggest that male and female song sparrows may differ in how they allocate resources to development of the immune system when reared in stressful or food-limited conditions.