Endocrine Response to Social Challenges in Northern and Southern Hemisphere Populations of the Crowned Sparrows, Zonotrichia (Emberizidae).

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Author(s)

• Wingfield, J. C.

Journal

Journal of Ornithology 147.5, Suppl. 1 (2006): 40-40.

Meeting Abstract

There is now extensive evidence that male-male interactions over territories and receptive mates can modulate secretion of testosterone. Furthermore, the pattern of response, or whether an individual responds at all, has been related to mating system. This pattern now appears to be found in most vertebrate taxa. How these patterns vary in relation to diverse habitats, however, is less well known. Field investigations of several taxa of closely related emberizines, the crowned sparrows (Zonotrichia), which occur from the arctic tundra of Alaska to Tierra Del Fuego at the southern tip of South America, show a tremendous variation in altitudinal and latitudinal range, particularly in North America. At high latitudes at the limits of their distribution, breeding seasons are brief and circulating testosterone levels are not socially modulated. Far northern males of Zonotrichia actually become insensitive to the behavioral effects of testosterone, possibly as a mechanism for maintaining paternal care. At mid-latitudes, most, but not all, males exhibit social modulation of testosterone secretion, especially in response to experimental challenges. In contrast, populations of the Rufous-collared Sparrow (Zonotrichia capensis) in Central and South America show a fixed pattern of testosterone secretion that is not socially modulated. Such variation in pattern and degree of social modulation appears to be independent of mating system and thus offers an ideal opportunity for comparing populations to determine the ecological basis of this variation, evolution of these patterns and the mechanisms underlying them.