Document Type

Article

Publication Title

Physiological and Biochemical Zoology

Publication Date

9-2009

Volume

82

Issue

5

Disciplines

Biology | Life Sciences

Abstract

White-throated sparrows (Zonotrichia albicollis) exhibit a genetic polymorphism that affects plumage and behavior in both sexes. White-striped morphs are more territorially aggressive, whereas tan-striped morphs provision nestlings at a higher rate. We investigated testosterone physiology in this species in an effort to understand hormonal mechanisms for the observed differences in aggression and parental care between the morphs. We found a small but significant difference in plasma testosterone between free-living white-striped and tan-striped males over the course of the breeding season. This difference correlates with previously observed differences in aggressive behavior and suggests that testosterone may mediate these differences. Testosterone remained higher in white-striped males relative to tan-striped males when males were provisioning nestlings and fledglings. Thus, testosterone may also contribute to the relatively reduced levels of parental care exhibited by white-striped males. In contrast to males, plasma testosterone did not differ between free-living white-striped and tan-striped females, which suggests that testosterone does not mediate differences in aggression between female morphs. Injection with gonadotropin-releasing hormone led to greater testosterone secretion in both captive and free-living males and captive females but did not differ by morph. Therefore, we conclude that differences in plasma testosterone between the morphs are due to differences in testosterone regulation upstream of the pituitary.

DOI

10.1086/605392

Comments

© 2009, University of Chicago Press.

Rights

© 2009, University of Chicago Press.

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