Integrative tracking methods elucidate the evolutionary dynamics of a migratory divide.

Area of Science:

• Evolutionary Biology
• Ornithology
• Speciation Studies

Background:

• Migratory divides are crucial for understanding bird speciation.
• Studying these divides is challenging due to the small size of many migratory birds.

Purpose of the Study:

• Investigate a migratory divide in hermit thrushes (Catharus guttatus).
• Examine the role of migration patterns in reproductive isolation and speciation.

Main Methods:

• Integration of genetic, geolocator, and morphological data.
• Analysis of genetic divergence between migratory populations.
• Tracking of migratory routes and overwintering locations using geolocators.

Main Results:

• High genetic divergence indicates secondary contact between historically isolated populations.
• Geolocators revealed distinct overwintering sites and migratory distances.
• A diagnostic genetic marker identified an intermediate nonbreeding location for hybrid zone birds, correlating with lower return rates.

Conclusions:

• The migratory divide in hermit thrushes is a region of secondary contact with evidence of incipient speciation.
• Divergent migratory patterns may act as a reproductive isolating mechanism.
• Lower hybrid fitness is potentially linked to intermediate migratory routes.