Pre- and Postnatal Effects of Corticosterone on Fitness-Related Traits and the Timing of Endogenous Corticosterone Production in a Songbird

Abstract

Maternally derived corticosterone in the egg and corticosterone produced endogenously by altricial nestling birds play essential roles during development. Although persistently high corticosterone levels can be harmful, moderately elevated levels above baseline can lead to reallocation of resources between growth and maintenance to ensure immediate survival or to enhance the development of fitness-related traits. We tested two hypotheses concerning the fitness consequences of elevated corticosterone during prenatal and postnatal development in altricial house wrens: (1) elevated corticosterone shifts resources away from growth and immune function and (2) elevated corticosterone serves as a signal to allocate resources to fitness-related traits. We also explored the development of the stress response, hypothesizing that early-stage nestlings have little endogenously produced corticosterone, but that their baseline and stress-induced corticosterone levels increase with age. Nestlings hatching from corticosterone-injected eggs were lighter at hatching, but through compensatory growth, ended up heavier than controls near the time of fledging, an important, fitness-related trait. Nestlings that hatched from corticosterone-injected eggs and those given oral doses of corticosterone did not differ from controls in three other fitness-related traits: immunoresponsiveness, size, or haematocrit. Early- and late-stage nestlings had similar baseline corticosterone levels, and all nestlings increased their plasma corticosterone levels in response to a capture-and-restraint protocol, with older nestlings mounting a stronger stress-induced response than younger nestlings. These results suggest that prenatal exposure to corticosterone is important in shaping offspring phenotype and are consistent with the hypothesis that maternally derived corticosterone in the egg can have long-term, fitness-related effects on offspring phenotype.

Figure 1

The relationship between the time taken to obtain a blood sample and circulating corticosterone concentration in brood-day 6 and brood-day 11 nestlings.

Figure 2

Brood-day 11 mass (LS mean ± SE) of late-stage nestlings following pre-natal manipulation of corticosterone. Controls received the vehicle, lows received a dose one standard deviation above mean yolk corticosterone, and highs received a dose two standard deviations above mean yolk corticosterone.

Figure 3

Circulating corticosterone concentations after post-natal oral administration of corticosterone. Circulating corticosterone concentration (LS mean ± SE) in brood-day 11 (late-stage) nestlings 10 min after receiving post-natal treatment. Controls received the vehicle and the experimental received corticosterone dissolved in the vehicle.

Figure 4

Stress-induced responses of brood-day 6 and brood-day 11 nestlings. Circulating corticosterone concentrations (LS mean ± SE) in response to capture-and-restraint protocol for brood-day 6 and brood-day 11 nestlings.