Incubation temperature can have profound effects on growth and development of embryos and young birds. However, few studies have examined the role that cycling incubation temperature may play in phenotypic variation and whether these effects persist to adulthood. We incubated Japanese quail eggs at control temperatures (37.5°C), at low temperatures (36.0°C), and under a cyclical treatment that maintained the same average temperature as the low treatment (36.0°C) with high temperatures that were the same as the control (37.5°C) and low temperatures that still allowed for development of the embryo (28.0°C). Individuals in the low treatment group were smaller in mass and size than individuals in the control group but had an increased basal metabolic rate relative to individuals in the cyclical treatment group. Temperature cycling offset the effects of low incubation temperatures on metabolic rate and embryonic development but not the effects on adult mass and size. Although Japanese quail are sexually size dimorphic, with females larger than males, we could detect no evidence of sex-specific sensitivity to suboptimal incubation temperatures. These results highlight the importance of incubation temperature and pattern as sources of morphological and physiological variation of adult birds.

Female birds transfer maternally derived antibodies (matAb) to their nestlings, via the egg yolk. These antibodies are thought to provide passive protection, and allow nestlings to avoid the costs associated with mounting an innate immune response. To test whether there is an energetic benefit to nestlings from receiving matAb, we challenged adult female tree swallows (Tachycineta bicolor) prior to clutch initiation with either lipopolysaccharide (LPS) or saline (Control). Following hatching, one half of each female's nestlings were immunized on day 8 post-hatch with LPS or saline, and the 4-h post-immunization nestling metabolic rate (MR) was measured. There was no difference in either LPS-reactive antibodies or total Ig levels between offspring of immunized and non-immunized mothers on day 6 or 14 post-hatch, possibly reflecting a relatively short half-life of matAbs in altricial birds. Additionally, we found no evidence that nestlings from LPS-immunized mothers could avoid the growth suppression that may result from activation of an inflammatory response. Unexpectedly, we found that control nestlings from LPS mothers had higher resting MR than control nestlings of control mothers. We attribute the increased MR to the costs associated with a general non-specific enhancement of immune function in nestlings from LPS-immunized mothers. Consistent with enhanced immune function, nestlings of immunized mothers had a more robust inflammatory response to phytohaemagglutinin and higher fledging success. Our results suggest that maternal antigen exposure pre-laying can result in increased fitness for both mothers and offspring, depending on food availability.

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