Genome shock in a migratory songbird hybrid zone.

Hybrids between two subspecies of Catharus ustulatus show greater transposable element proportions, TE expression, and chromatin accessibility than parental lineages in migration-associated brain regions.

• Why it matters: The genome shock hypothesis is well supported in plants, but direct vertebrate evidence is limited, leaving uncertainty about whether hybridization destabilizes genome regulation in wild animals.
• What they did: Using whole-genome resequencing, RNA-seq, and ATAC-seq, the study quantified TE proportions, TE expression, and chromatin accessibility during migratory and non-migratory states in two brain regions.
• The result: TE expression and chromatin accessibility were positively correlated across states and regions, with context-dependent pattern strength, and shock signatures linked to regulatory regions and retinoic acid receptor signaling.