Processes underlying complex patterns of song trait evolution in a Setophaga hybrid zone

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Bioacoustics

Background:

• Hybrid zones present unique evolutionary pressures.
• Mating and aggressive signals may evolve under different selective forces.
• Birdsong in *Setophaga* warblers serves dual roles in mate attraction and territory defense.

Purpose of the Study:

• To investigate the evolutionary trajectories of birdsong components in an avian hybrid zone.
• To determine the relative importance of song rhythm and syllable morphology in mate attraction and territorial defense.
• To understand how different song modules evolve under opposing selective pressures.

Main Methods:

• Geographic cline analyses across the hybrid zone.
• Playback experiments to test song function in mate attraction and defense.
• Analysis of song rhythm and syllable morphology patterns.

Main Results:

• Asymmetric introgression of song rhythm observed, with rhythm more critical for mate attraction.
• Syllable morphology showed little importance in either mate attraction or defense.
• Song features converged, but distinct geographic patterns for rhythm (clinal) and morphology (mosaic) suggest different inheritance and learning modes.

Conclusions:

• Opposing selective forces (mate attraction vs. territory defense) act independently on distinct song modules.
• Song rhythm and syllable morphology exhibit different evolutionary dynamics due to varying roles and inheritance mechanisms.
• Learned and innate components of birdsong contribute to complex evolutionary patterns in hybrid zones.