The effect of capture-and-handling stress on carotenoid-based beak coloration in zebra finches
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Stress can have widespread effects on animal behaviors and phenotypes, including sexually selected traits. Ornamental colors have long been studied as honest signals of condition, but few studies have been conducted on how the physiological stress response (i.e., corticosterone (CORT) elevation) impacts color expression. We used a traditional capture-and-restraint technique to examine the effect of repeated handling stress on carotenoid-dependent beak coloration in male and female zebra finches (Taeniopygia guttata). Birds subjected to daily, 10-min handling treatments, which elevated circulating CORT levels, for a four-week period displayed deeper orange/red beak coloration than did control animals. Stressed males lost body mass during the experiment and marginally decreased in circulating carotenoid concentrations. Hence, handling stress may have reduced food intake or induced mobilization of body stores (i.e., fat) of carotenoids. In contrast to males, stressed females maintained orange beak color, while control females faded in color. This study highlights sex- and pigment-specific mechanisms by which stress may temporarily enhance the expression of sexual traits, but at the expense of other key fitness traits (e.g., body mass maintenance, reproduction).
KeywordsBody mass Carotenoids Corticosteroids Sexual selection Taeniopygia guttata
We thank P. Deviche and H. B. Fokidis for assistance with running CORT assays, and P. Deviche, M. Moore, M. Butler, and two anonymous referees for offering constructive comments on the manuscript. All procedures reported here were approved by Arizona State University’s Institutional Animal Care and Use Committee (protocol # 05-764R). Work by AL on this project was funded by ASU-York University Summer Internship Exchange Program. Work by KL on this project was funded by ASU’s Barrett Honors College. Experiments on males (by AL) and on females (by KL) were completed in partial fulfillment of undergraduate honor’s theses at these author’s respective institutions.
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