Grieg & Webster 2014

Introduction

  • Title: The evolution of fairy-wren songs from predator to display contexts

  • Authors: Emma I. Greig, Michael S. Webster

  • Affiliations: Cornell Lab of Ornithology and Department of Neurobiology & Behavior, Cornell University, Ithaca, NY, U.S.A.

  • Published: Animal Behaviour, 2014

Key Concepts

  • Evolutionary Biology Challenge: Understanding origins of novel traits is a significant challenge.

  • Context Shifts: Shifts from predator signaling to conspecific advertisement may lead to novel functions, pressures, and phenotypes.

  • Fairy-Wren Behavior: Several fairy-wren species respond to predators with song-like trills that also serve a display function.

Hypotheses Examined

  1. Hypothesis 1: Type II songs originated as antipredator signals, later shifted to display context, and became more elaborate.

  2. Hypothesis 2: Type II songs began as conspecific-directed displays that shifted to exploit predator contexts.

Findings

  • Predator Response: Many fairy-wrens give predator-elicited trills, but only some display unprompted trills during dawn choruses.

  • Ancestral Context: Ancestral state reconstructions indicated that predator-elicited contexts evolved before conspecific display contexts.

  • Trill Performance: Species using trills more frequently often have longer trills with faster note rates, indicating heightened performance associated with display importance.

Factors Influencing Novel Trait Evolution

  • Genetic Mutation and Plasticity: These are significant sources of novelty leading to heritable phenotypic changes.

  • Cultural Component of Traits: Learned behaviors (e.g., birdsong) may evolve from copying errors or improvisation.

  • Contextual Changes: Changes in signal context or function can affect the persistence of novel traits.

Contextual Pressures on Signals

  • Predator vs. Display Signals: Typically, conspicuous mating behaviors are suppressed under predation risk, but there are exceptions.

  • Behavior Relevance: Antipredator behaviors might sometimes become advertisements, conveying signaller quality or status.

Study Species: Malurus Fairy-Wrens

  • Species Overview: Four fairy-wren species are known to give a trill (Type II song) in response to vocal predator signals.

  • Display vs. Alarm Function: In some species, trills do not serve a mobbing or alarm function but act as displays directed to conspecifics.

Research Methods

  • Field Methods: Conducted in Australia during the breeding season (Nov 2010 - Jan 2011). Recorded dawn choruses and used playback stimuli.

  • Playback Experiments: Examined reactions to predator and non-predator stimuli, comparing contexts and species.

  • Acoustic Analysis: Five key parameters measured: number of notes, note intervals, duration of each note, duration of trills, and bandwidth.

Results Overview

  • Trilling Frequencies: Found varying frequencies of trills across species in predator-prompted and dawn chorus contexts.

  • Performance Correlation: Higher trill performance correlated with greater use in display contexts.

  • Ancestral State Reconstruction: Suggested that predator-elicited trills likely developed before dawn chorus displays.

Evolutionary Implications

  • Signal Context Shift: Results indicate a shift from predator-related signaling to incorporation into display dynamics, supporting Hypothesis 1.

  • Functional Assessment: Future research should experimentally test functions of predator-context trills to differentiate between scenarios.

  • Broader Context: Connectivity between predator and display signaling offers a valuable avenue for understanding evolutionary signaling dynamics.

Conclusion

  • Novel Traits: The study illustrates how shifts in signaling contexts lead to new signal phenotypes with significant evolutionary implications.

  • Moving Forward: Further investigations into geography, habitat use, and cultural history of signals across different species are recommended.