A comparison of the adrenocortical responses to acute stress in cardueline finches from the Tibetan Plateau, Arctic Alaska and lowland Western North America

Abstract

In many avian species, it has been well demonstrated that individuals attempting to breed in harsh or unpredictable environments always express reduced adrenocortical responses to acute stress, whereas those breeding in more benign or predictable environments may show more robust responses. However, fewer studies have focused on comparing closely related species that express similar behavioral traits (e.g., territorial behavior, mating system, nestling behavior) and ecological traits (e.g., habitats, food resources) among different breeding environments. In closely related taxa, we hypothesized that those species breeding in benign environments would show greater adrenocortical responses to acute stress compared with their congeners breeding in harsh environments. In this study, we examined seasonal and sex differences in baseline and stress-induced plasma corticosterone (CORT) levels in four cardueline finch species from Arctic Alaska (reanalysis of previously published data from the Common Redpoll, Carduelis flammea, at high latitude habitats), the Tibetan Plateau (Twite, C. flavirostris, from high altitude, mid-latitude habitats), and western North America (American Goldfinch, C. tristis, and Pine Siskin, C. pinus, from mid-latitude and low altitude habitats). Our results showed that (1) Twites had lowered adrenocortical responses during the pre-basic molt stage than the early breeding stage, both sexes of American Goldfinch and Pine Siskin showed similar patterns of adrenocortical responses between the early breeding and the late breeding stages, whereas Common Redpolls expressed significantly lowered adrenocortical responses during the late breeding stage; and (2) unexpectedly, there were no significant differences in baseline or stress-induced CORT (maximal CORT, total integrated and corrected integrated CORT levels) levels among Twites, American Goldfinches, Pine Siskins, and Common Redpolls during the early breeding stage or among American Goldfinches, Pine Siskins and Common Redpolls during the late breeding stage. This similar pattern in adrenocortical responses may reflect the stability of physiological functions of CORT during long-term evolutionary adaptation. It also provides us with an opportunity to understand the potential effects of phylogenetic relationships on the modulation of adrenocortical responses to acute stress in free-living birds. Whether phylogenetic effects are a common or casual phenomenon remains to be determined in other closely related taxa.