Plumage coloration, aerobic capacity and the spatial dynamics of courtship in satin bowerbirds (Ptilonorhynchus violaceus)
Savard, Jean-Francois Louis
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Courtship is the focal activity of mate-choice and is often composed of multiple elements under sexual selection. Bowerbirds are an important model system in sexual selection and I investigated three elements of courtship in satin bowerbirds (Ptilonorhynchus violaceus): plumage coloration, aerobic capacity and the spatial dynamics of courtship. How plumage coloration affects mate-choice has long been discussed in bowerbirds but previous studies haven't found the presumed relationships. Adult males have iridescent, short wavelength saturated blue-black plumage with peak reflectance in the ultraviolet (UV). Here I show that blue, not UV, plumage reflectance is related to mating success. This suggests a mismatch between peak plumage reflectance and female preference and that it's not safe to infer a role of UV in mate-choice simply because of relatively high UV reflectance. Physiological traits like aerobic capacity are of special interest in sexual selection because they indicate whole-organism performance. Adult male VO<sub>2max</sub> predicts male display quality but not mating success. VO<sub>2max </sub> has an effect on male display quality that is not reflected in the relationship between display quality and mating success, suggesting that female choice may be directed at other male qualities. If any general trends are to be expected regarding aerobic capacity and courtship, I believe that simple repetitive courtships may be used as tests of male physiological ability, but that complex courtships involving multiple elements may have evolved to indicate male qualities other than whole-organism performance. To study the spatial dynamics of courtship, I used vertically mounted cameras above bowers. I found a spatial pattern of male courtship and an association between male movements and the use of the bower as a barrier. This spatial pattern was associated to female startling behavior and males responded to robot startles by moving farther away from females. These findings support the hypothesis that male courtship behavior reduces the threat to females during courtship. Aggressive displays are commonly co-opted for courtship and threat reduction offers a testable hypothesis that can help understand the adaptive significance of the complex and what can otherwise be thought of as arbitrary courtships of many animals.