Nonrandom dispersal drives phenotypic divergence within a bird population.

Area of Science:

• Evolutionary Biology
• Ecology
• Animal Behavior

Background:

• Gene flow is traditionally viewed as a homogenizing force in evolution.
• Recent studies suggest directional gene flow can promote divergence.
• Understanding microevolutionary processes requires examining gene flow at fine spatial scales.

Purpose of the Study:

• To investigate phenotypic differentiation in pied flycatchers (Ficedula hypoleuca) over two decades.
• To assess the role of directional gene flow in maintaining phenotypic variation at a small spatial scale (1.1 km).
• To explore the relationship between habitat preference, body size, and dispersal patterns.

Main Methods:

• Long-term monitoring (over 20 years) of pied flycatcher populations in adjacent deciduous and coniferous habitats.
• Measurement of phenotypic traits, specifically body size (tarsus length).
• Analysis of dispersal patterns, including directionality and non-randomness with respect to body size.

Main Results:

• Consistent phenotypic differentiation in male body size between deciduous (larger) and coniferous (smaller) forest habitats.
• Evidence of non-random male dispersal influenced by body size, favoring larger males in preferred deciduous habitats.
• Directional gene flow appears to maintain phenotypic variation despite proximity of habitats.

Conclusions:

• Directional gene flow, coupled with habitat-specific preferences, can drive and maintain phenotypic divergence at microgeographic scales.
• Eco-evolutionary dynamics are influenced by dispersal patterns and habitat selection.
• Findings challenge traditional views on gene flow and highlight its complex role in microevolution.