MODULATION OF THE ADRENOCORTICAL RESPONSES TO ACUTE STRESS IN NORTHERN AND SOUTHERN POPULATIONS OF ZONOTRICHIA

Abstract

How animals respond to perturbations of the environment is relevant to the effects of global climate change and human disturbance. The physiological mechanisms underlying facultative responses to unpredictable perturbations of the environment will allow us to understand why some populations are able to cope more than others. This is important for basic biology as well as for conservation. Northern populations of White-crowned Sparrow (Zonotrichia leucophrys), show varying degrees of modulation of the adrenocortical response to acute stress early in the breeding season. These variations are related to a short breeding season at high latitudes and altitudes (up-regulation of the stress response), and possibly degree of parental care (down-regulation of the stress response). Investigations of many taxa from the northern hemisphere indicate these types of modulation are widespread among vertebrates. However, modulation of the adrenocortical response to stress is much less well-known in the southern hemisphere and Neotropical birds present an ideal model system to test whether patterns of hormonal responses to stress in the northern hemisphere are consistent worldwide. Equatorial, high altitude, populations of the Rufous-collared Sparrow (Z. capensis costaricensis), a southern congener of the White-crowned Sparrow, have long breeding seasons, but show no early breeding up-regulation of the adrenocortical responses to stress. This pattern is more similar to mid-latitude, low altitude, populations of White-crowned Sparrows. Whether austral high latitude and altitude populations of the Rufous-collared Sparrows modulate these processes, under presumably similar constraints of mid- to high latitude seasonality in the north, is currently under investigation.