Vermivora photographs in plumage genomic study

Hybrids with different combinations of traits can be used to identify the
genomic regions that underlie phenotypic characters important to species
identity and recognition. Here we explore links between genomic and
plumage variation in Blue-winged Warbler x Golden-winged Warbler hybrids,
which have traditionally been categorized into two discrete types.
"Lawrence’s Warbler" hybrids are very yellow overall, similar to
Blue-winged Warblers, but exhibit the black throat patch and face mask of
Golden-winged Warblers. "Brewster’s Warbler" hybrids are similar
to Golden-winged Warblers, but lack the black throat patch and face mask
and sometimes have yellow on their underparts. Previous studies
hypothesized that (1) first generation hybrids are of the Brewster’s type
and can be distinguished by the amount of yellow on their underparts, and
that (2) the throat patch/mask phenotype is consistent with Mendelian
inheritance and controlled by variation in a locus near the Agouti
signaling protein gene (ASIP). We addressed these hypotheses using whole
genome re-sequencing of parental and hybrid individuals. We found that
Brewster’s hybrids had genomic hybrid index scores that indicate this
phenotype can arise by majority ancestry from either parental species,
their plumage varied from low-to-high levels of carotenoid pigmentation,
and individuals captured in multiple years grew consistently less yellow
as they aged. Variation in carotenoid pigmentation showed little
relationship with genomic hybrid index and is thus inconsistent with
previous hypotheses that first generation hybrids can be distinguished by
the amount of yellow in their plumage. Our results also confirm that
variation near ASIP underlies the throat patch
phenotype, which we refined to a ~10-15 Kb region upstream of the coding
sequence. Overall, our results support the notion that traditional
categorization of hybrids as either Lawrence’s or Brewster’s
over-simplifies their genomic and continuous variation in carotenoid
pigmentation and is based primarily on one discrete trait, which is the
throat patch/mask phenotype.