Hypothalamus-pituitary interrenal axis sensitivity of subarctic wood frogs (Lithobates sylvaticus) and selected congeneric temperate species

A physiological response to stress is a process conserved among all vertebrate taxa. As a result of stress, glucocorticoids, especially corticosterone, are released into the blood stream where they bind to receptor cells to initiate a response to mediate the stressor. This process can limit or promote other life functions and redistribute energy reserves. Because of these effects, some populations likely have different sensitivities to stress. Understanding the sensitivity of this response can allow researchers to predict the impact a stressor may have on an organism. Plasma corticosterone from wood frogs (Lithobates sylvaticus) was quantified from subarctic and temperate populations in response to handling stress. Additionally, temperate populations of L. clamitans, L. catesbeianus, and L. sphenocephalus were sampled. Subarctic wood frogs had an acute increase in corticosterone after handling, but this increase did not significantly differ after ten minutes of confinement (up to 60 minutes). Neither energetic condition nor environmental variables strongly affected baseline corticosterone levels. Calling male wood frogs from both locations had elevated baseline corticosterone concentrations that did not change after handling, however concentrations were significantly higher in the temperate population. Differences in baseline and stress-induced corticosterone production existed among temperate congenerics. Results suggest that different populations of the same species, and different species in the same region have evolved different strategies to mitigate stressors.