Inbreeding and adaptation to captivity depress the response to stress

The success of reintroductions using captive-bred populations of wild species is potentially impacted by adaptations to non-natural captive environments. Little research has been done into how physiological traits change from wild to captive populations. We do not yet understand how glucocorticoid secretion patterns, a critical aspect of the stress response and other underlying life-history traits, change in the captive environment. Here we used 326 white-footed mice (Peromyscus leucopus) to test how the baseline concentrations of fecal glucocorticoid metabolites (fGM) change as this wild rodent adapts to captivity and becomes increasingly inbred over several generations. Breeding protocols did not influence FGM but showed a strong decrease with generations in captivity, an effect driven by both plastic and genetic effects. We also found that juvenile fGM concentrations strongly predict adult fGM concentrations. This allows intra-generation effects, such as habituation, to be transformed into inter-generation effects. Lastly, the relationship between inbreeding and baseline fGM concentrations suggests that the intensity of baseline adrenal activity and mounted stress response is positively associated with fitness. Also, because the relationship is significantly stronger for females than for males, the result gives us some insight into the sex-specific adaptive value of fGM concentrations.