Meeting Abstract
Physically elaborate social signals are believed to evolve because they reflect an individual’s quality by showcasing vigor, or an ability to produce energetically demanding behavior. However, many studies fail to uncover a relationship between vigor and individual variation in reproductive success. Here, we use the downy woodpecker to experimentally test an alternative hypothesis, which posits that physical displays evolve in response to sexual selection for motor skills. This species communicates with conspecifics by rapidly and repeatedly striking their bills against resonate surfaces at approximately 15 Hz (strikes/second), and the result is a sonation, called a drum, which is used for territorial signaling. We therefore modulate the acoustic parameters of the drum that represent underlying motor skill. Specially, we generated drums that either included more beats or a shorter duration between two beats to assess how these factors influence territorial behavior of resident birds. Our findings demonstrate that slightly longer and faster drums elicit a more robust aggressive response, suggesting that breeding pairs evaluate aspects of the drum that are reliant on motor skill when deciding how to respond to competitors. Furthermore, using quantitative PCR, we illustrate that at least one physiological adaptation that may enhance motor command, the amount of androgen receptor expressed in a skeletal muscle, is associated with the downy woodpecker’s neck musculature. These data collectively suggest that sexual selection for motor skill is associated with the emergence of an elaborate physical display in woodpeckers.
