Convergent evolution in social swallows (Aves: Hirundinidae)

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Comparative morphology

Background:

• Behavioral shifts can drive evolutionary changes, pushing species into new adaptive zones.
• While ecological behaviors are well-studied, the impact of social behaviors on morphology is less understood.
• Swallows and martins (Hirundinidae) display diverse social structures, from solitary to colonial.

Purpose of the Study:

• To investigate how shifts in breeding and foraging social behavior have influenced morphological evolution in Hirundinidae.
• To determine if sociality, particularly in breeding and foraging, correlates with specific morphological adaptations in swallows.

Main Methods:

• Utilized a well-resolved phylogenetic tree of Hirundinidae.
• Compiled a database of social behaviors (solitary vs. colonial breeding/foraging).
• Analyzed morphological measurements using a threshold model of discrete state evolution.

Main Results:

• Shifts in breeding and foraging social behavior are frequent across the swallow phylogeny.
• Social swallows exhibit significantly less morphological variance compared to solitary swallows.
• Strong morphological convergence was observed in social swallows, particularly those foraging socially, with smaller physical traits.

Conclusions:

• Social behavior is a significant driver of morphological evolution in swallows, impacting variance and promoting convergence.
• Morphological adaptations in social swallows likely enhance maneuverability, foraging efficiency, and reduce collisions during flight.
• This study underscores the evolutionary importance of sociality beyond eusocial insects and primates.