Character displacement of a learned behaviour and its implications for ecological speciation

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Ornithology

Background:

• Cultural evolution's role in speciation is mainly studied in allopatric contexts.
• Speciation with gene flow, particularly via cultural transmission, is less understood.
• Red crossbills (Loxia curvirostra) exhibit learned vocalizations, offering a model system.

Purpose of the Study:

• To investigate cultural evolution's role in non-allopatric speciation in Cassia crossbills (Loxia sinesciuris).
• To test if learned vocalizations drive reproductive isolation via character displacement.
• To assess the impact of reduced heterospecific flocking on assortative mating and speciation.

Main Methods:

• Documented population-level divergence in Cassia crossbill call structure over two decades.
• Conducted field experiments to assess crossbill responses to evolved call differences.
• Analyzed the relationship between call divergence, heterospecific flocking, and assortative mating.

Main Results:

• Observed substantial population-level divergence in Cassia crossbill calls within 20 years.
• Demonstrated that Cassia and red crossbills differentially respond to evolved call structures, reducing heterospecific flocking.
• Found that reduced heterospecific flocking likely increases assortative mating.

Conclusions:

• Adaptive cultural evolution of vocalizations can drive reproductive isolation in sympatric populations.
• Character displacement in learned calls facilitates speciation with ongoing gene flow.
• This mechanism provides evidence for a potentially widespread pathway to speciation.