Historical diversification of migration patterns in a passerine bird

Area of Science:

• Evolutionary biology
• Ornithology
• Population genetics

Background:

• Bird migration involves complex traits like orientation and life-history adjustments.
• Understanding the evolutionary speed of these combined traits is crucial.

Purpose of the Study:

• To investigate the evolutionary rate of complex migratory strategies in blackcaps (Sylvia atricapilla).
• To determine the genetic basis and historical factors shaping divergent migratory behaviors.

Main Methods:

• Analysis of mitochondrial control-region DNA sequences from 241 blackcaps across 12 populations.
• Comparison of genetic structure among sedentary, migratory, and geographically distinct populations.
• Mismatch-distribution analyses to infer population expansion and timing.

Main Results:

• No significant genetic structure found between migratory and sedentary blackcap populations or across broad biogeographic areas.
• Evidence of genetic structure identified across the central European migratory divide.
• Independent evolution of divergent migratory strategies supported, linked to postglacial colonization routes.
• Expansion dated to the last postglacial period, originating from a small population size.
• Gibraltar populations showed restricted gene flow and stable population size, suggesting a refuge.

Conclusions:

• Interruption of gene flow is not required for maintaining migratory polymorphism in blackcaps.
• Highly divergent migratory strategies can evolve relatively quickly in response to historical environmental changes.
• Postglacial recolonization routes played a key role in shaping current migratory diversity.