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Functional Significance and Motor Control of Drumming Behavior in Downy Woodpeckers

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title
Functional Significance and Motor Control of Drumming Behavior in Downy Woodpeckers
author
Schuppe, Eric Robert
abstract
Animals often court females and compete with rivals by producing elaborate body and limb movements. Although the use of movement (e.g., gestural communication) for social signaling is one of the most ubiquitous forms of communications in the animal kingdom, we still know little about how and why these displays evolve. To address this gap in our knowledge, I used the downy woodpecker (Dryobates pubescens) – a bird that produces an aggressive gestural display known as a drum. The drum is a staccato-like sonation that echoes throughout the forest and is generated when the bird rapidly and repeated hammers its bill against a tree. To investigate the functional significance of this display, we constructed recordings with differences in two of the main components of this signal: drum length and speed. Birds produce a more robust aggressive response when they hear longer or faster drums, suggesting that birds perceive individuals capable of producing these more physically demanding signals as more threatening. Thus, selection likely favors high performance signals, which increase competitiveness during territorial interactions. At the same time, selection for these rapid movements shaped muscular design. In particular, two Ca2+ handling mechanisms that aid in rapid muscle relaxation are specialized in the woodpecker neck muscle that controls drumming (longus colli [LC]). Next, we investigated how androgenic signaling systems evolved to support drumming. First, we found that presence of drumming across species was correlated with increased androgen receptor levels in the LC, with testosterone levels changing seasonally to (presumably) activate drumming behavior. We also found that the woodpecker LC muscle expresses all the molecular components necessary for de novo androgen synthesis. This suggests that this display muscle may be specialized to regulate its own androgen exposure independent of gonadal secretions. Finally, we uncovered putative pre-motor and forebrain substrates that are associated with the production of drumming. We predict that these forebrain nuclei contribute to the animal’s ability to rapidly refine its display across social contexts. Collectively, this work significantly advances our understanding about why selection elaborates movement for social communication and the underlying mechanisms that produce these motorically complex social displays.
subject
androgens
downy woodpecker
Drumming
muscle
testosterone
contributor
Fuxjager, Matthew J (committee chair)
Fahrbach, Susan (committee member)
Goller, Franz (committee member)
Johnson, Erik (committee member)
Muday, Gloria (committee member)
date
2019-09-05T08:35:30Z (accessioned)
2019 (issued)
degree
Biology (discipline)
embargo
2024-09-01 (terms)
2024-09-01 (liftdate)
identifier
http://hdl.handle.net/10339/94325 (uri)
language
en (iso)
publisher
Wake Forest University
type
Dissertation

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