Animal signals are complex, comprising multiple components that receivers may use to inform their decisions. Components may carry information of differing value to receivers, and selection on one component could modulate or reverse selection on another, necessitating a multivariate approach to estimating selection gradients. However, surprisingly few empirical studies have estimated the strength of phenotypic selection on complex signals with appropriate design and adequate power to detect nonlinear selection. We used phonotaxis assays to measure sexual selection on the advertisement signal of Cope's gray tree frog, Hyla chrysoscelis. Female preferences were assessed for five signal components using single- and two-stimulus behavioral assays. Linear, quadratic, and correlational selection gradients were estimated from the single-stimulus data. Significant directional selection is acting on call duration, call rate, pulse rate, and relative amplitude; stabilizing selection is acting on call duration and call rate. Under the two-stimulus paradigm, conclusions were qualitatively different, revealing nonlinear selection on all components except call duration. For individual subjects, the outcomes of single- and two-stimulus trials were frequently discordant, suggesting that the choice of testing paradigm may affect conclusions drawn from experiments.
Bibliographical noteFunding Information:
We are grateful to all members of the Bee lab 2013?2015 for assistance with collecting frogs and running trials; to the Three Rivers Park District for access to field sites; to Charles J. Geyer for discussion of analyses; and to H. Carl Gerhardt, Norman Lee, James Tumulty, and Marlene Zuk for helpful comments on an earlier draft of the manuscript. This study is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 00039202 and a grant to MAB (IOS-1452831). Additional support was provided by a Minnesota Herpetological Society Research Grant, an American Society of Ichthyologists and Herpetologists Gaige Award, and a Ford Foundation Pre-Doctoral Fellowship to JCT. JCT, JLW, and MAB designed the experiment. JCT made the synthetic stimuli, conducted the experiment, and wrote the manuscript. All authors contributed to the analysis and interpretation of the data and commented on the manuscript. The doi for our data is https://doi.org/10.5061/dryad.n50cr.
© 2017 The Author(s). Evolution © 2017 The Society for the Study of Evolution.
- Acoustic signals
- animal communication
- gray treefrog
- selection analysis
- sexual selection
- sexual signaling
- stabilizing selection