Year of Award
Doctor of Philosophy (PhD)
Organismal Biology and Ecology
Department or School/College
Division of Biological Sciences
Creagh W. Breuner
Douglas J. Emlen, Erick Greene, Thomas E. Martin, Hubert G. Schwabl
behavioral polymorphism, corticosterone, corticosterone binding globulin, testosterone, White-throated sparrow, Zonotrichia albicollis
University of Montana
In this body of work, I examine how testosterone (T) physiology mediates the life-history trade-off between mating effort and parental care in the White-throated Sparrow. This species exhibits a behavioral polymorphism that occurs in both sexes. White-striped (WS) morphs are more territorially aggressive, sing more frequently and seek more extra-pair copulations. Tan-striped (TS) morphs provision nestlings more frequently. Thus this species roughly illustrates the trade-off between mating effort and parental care. I examine T physiology on three levels: plasma titres, binding globulins and response to the social environment. I ask whether levels of T correlate with morph-specific behavior and does this relationship change with stage in the nesting cycle. I found that WS males have significantly higher plasma levels of T than TS males. This difference is small, but it persisted through the parental stage of the nesting cycle. This suggests that T may mediate differences in mating effort and parental behavior in males, but is likely not the only factor. Female morphs did not differ in plasma T, thus T does not appear to play a similar role in females. Next I ask how corticosterone binding globulin (CBG) modulates T action. I found that CBG binds over 90% of T and is an important modulator of T action in this species. However CBG capacity did not differ between morphs, nor did morphs differ in baseline levels of corticosterone (CORT, a stress hormone that competes with T for binding sites on CBG.) Therefore interactions with CBG and CORT do not affect T action differently in the morphs, and patterns of free T (T not bound to CBG) mirror patterns of total T. Finally I investigated how T physiology responds to a change in the social environment- the establishment of a dominance relationship. WS males exhibited aggression more frequently and tended to dominate TS males. Levels of total T, CBG, CORT and free T were not predictive of future dominance status. Nor did these measures show persistent changes once the dominance relationship was established. The response of T physiology to the formation of a dominance relationship did not differ between morphs.
Swett, Meredith Bettencourt, "Hormonal Mediation of a Unique Behavioral Polymorphism in the White-throated Sparrow (Zonotrichia albicollis)" (2007). Graduate Student Theses, Dissertations, & Professional Papers. 1246.
© Copyright 2007 Meredith Bettencourt Swett