Repeatable Selection on Large Ancestry Blocks in an Avian Hybrid Zone.

Area of Science:

• Evolutionary Biology
• Population Genetics
• Speciation

Background:

• Hybrid zones serve as natural laboratories for studying genetic incompatibilities between species.
• Swainson's thrush subspecies present a unique case due to distinct migration routes and hybrid migratory failure, suggesting ecological isolation.

Purpose of the Study:

• To identify loci and genomic regions under selection within the Swainson's thrush hybrid zone.
• To investigate patterns of introgression and their relationship with genetic incompatibilities and evolutionary history.

Main Methods:

• Utilized a panel of ancestry-informative markers to analyze genetic variation across four hybrid populations.
• Examined genomic clines and transitions between subspecies ancestry to detect selection signatures.
• Assessed the influence of genomic structural features and recombination rates on selection and introgression.

Main Results:

• Identified two large genetic blocks on chromosomes 1 and 5 exhibiting repeatable patterns of selection against incompatibilities.
• Observed differential introgression patterns within these blocks, with chromosome 1 showing inland subspecies introgression and chromosome 5 showing coastal subspecies introgression.
• Found that genomic regions with low recombination, high subspecies differentiation, and positive selection experienced stronger selection and reduced introgression.

Conclusions:

• Linkage among loci interacts with divergent selection and prior evolutionary divergence to reinforce reproductive isolation.
• Genomic structural features and evolutionary history play a crucial role in shaping selection and introgression patterns within hybrid zones.
• Ecological incompatibilities, particularly related to migration, contribute significantly to maintaining the Swainson's thrush hybrid zone.