Data from: Similar hybrid composition among different age and sex classes in the Myrtle–Audubon's warbler hybrid zone

Hybrid zones provide a key natural context within which to study the
barriers between incipient species. In some avian hybrid zones, there is
indirect evidence of selection against hybrid offspring, yet the source of
that selection is often unclear. We examined the frequency distribution of
hybrids between Myrtle Warblers (Setophaga coronata coronata) and
Audubon's Warblers (S. c. auduboni), using data to quantify—for the
first time at a genomic scale—the composition of hybrids in this hybrid
zone. We sampled birds during the breeding season and during fall
migration and compared the frequencies of hybrids of different sex and age
classes. Specifically, we tested for evidence of early-generation hybrids
being significantly under- or over-represented in any of these classes, as
would be expected if hybrids have lower or higher fitness than
non-hybrids. We found that the genomic composition of birds in the hybrid
zone spans the full ancestry spectrum. Across all our sampling periods, we
found an excess of birds that had more Audubon's ancestry, with a
stronger bias toward Audubon's ancestry in fall migrants than in
breeding birds, consistent with asymmetric introgression. Notably, we did
not find any differences in hybrid frequencies between juvenile and adult
age classes or between males and females. Therefore, our results do not
support large differences in viability between male and female hybrids or
between different age classes of hybrids.