Dissertation
Causes and consequences of variable testosterone in two Fairywren species
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000003166
Handle:
https://hdl.handle.net/2376/122346
Abstract
Sex steroids like testosterone can mediate multiple traits underlying alternate phenotypes. For instance, seasonal increases in testosterone can facilitate molt into ornamental plumage and expression of territorial and sexual behavior in many male birds. In chapter 2 I capitalize on naturally occurring wildfires prior to the breeding season to test whether male Red-backed Fairywrens (Malurus melanocephalus) are plastic in their timing of testosterone-mediated production of ornamentation. I found that suppressed testosterone circulation inhibits, or at least greatly delays acquisition of ornamentation. Whether mechanisms of ornament production are shared among sexes of closely related species is poorly understood and is explored in chapter 3. I use a testosterone supplementation experiment to determine if elevated testosterone causes unornamented female White-shouldered Fairywrens (Malurus alboscapulatus) to molt ornamental plumage and express elevated territoriality consistent with the naturally occurring ornamented female phenotype. I found that testosterone-implanted females develop partial ornamentation followed by enhanced territoriality. Finally, to test among the leading hypotheses about what causes rapid elevations of testosterone circulation, I use a combination of correlative and experimental approaches in male White-shouldered Fairywrens. I first show that males of the unornamented female lorentzi subspecies circulate greater mean testosterone and score higher in four of five metrics for social interaction relative to males of the ornamented female moretoni subspecies. Then I use an experiment to test which social interactions cause elevated testosterone and find that males captured while actively courting females have significantly greater plasma testosterone than males captured during active territory defense or males that were flushed into nets absent a social stimulus. Taken together, I find that both the physical and social environment contribute to variation in testosterone circulation, thus causing downstream effects to ornamentation and associated behavior.
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Details
- Title
- Causes and consequences of variable testosterone in two Fairywren species
- Creators
- Jordan Boersma
- Contributors
- Hubert Schwabl (Advisor)Patrick A Carter (Committee Member)Erica J Crespi (Committee Member)Heather E Watts (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Biological Sciences, School of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 140
- Identifiers
- 99900652005101842
- Language
- English
- Resource Type
- Dissertation