What determines a warbler's colors?
Researchers use hybrid birds to narrow genetic region underlying
difference in color between blue-winged and golden-winged warblers

Date:
July 14, 2020
Source:
Penn State
Summary:
A new study has narrowed down the region of the genome that drives
the black color in throat and face of warblers by studying the
hybrid offspring produced when two species mate. The hybrids of
golden-winged and blue-winged warblers have a mix of coloration
from the parent species, which allows researchers to identify which
regions of the genome are associated with which color patterns. The
study also reveals a more complex basis for the amount of yellow
in warbler bellies and raises concerns about how hybrids of these
species are classified.



FULL STORY ==========================================================================
A new study has narrowed down the region of the genome that drives
the black color in throat and face of warblers by studying the hybrid
offspring produced when two species mate. The hybrids of golden-winged and blue-winged warblers have a mix of coloration from the parent species,
which allows researchers to identify which regions of the genome are
associated with which color patterns.

The study, led by researchers at Penn State, also reveals a more complex
basis for the amount of yellow in warbler bellies and raises concerns
about how hybrids of these species are classified.


========================================================================== Their results appear online in the journal The Auk: Ornithological
Advances.

"The distinct plumage of these otherwise very similar birds has
perplexed ornithologists for more than a hundred years," said Marcella
Baiz, postdoctoral researcher at Penn State and first author of the
paper. "Our research team previously compared the genomes of golden-winged
and blue-winged warblers and identified 6 regions that differed between
them, some of which may control color. In this study, we used hybrid
birds of these species, which mix and match the features of their parent species, to help identify which regions of the genome are associated
with which color patterns." Color is an important cue for warblers and
is prominently displayed during mating and other behaviors. Blue-winged warblers have yellow throats and bellies, while golden-winged warblers
have white bellies and a black throat patch and face mask. Hybrids of
these species vary in amounts of yellow and whether they have a black
face mask and throat, and these characteristics are commonly used to
categorize birds into different classes of hybrids.

The research team rated hybrid birds based on their plumage color and
genetic likeness to the two parental species. They found that the amount
of yellow in hybrids, which is produced by pigments called carotenoids,
is not directly related to a bird's genetic likeness to the parent
species -- for example, hybrids with more yellow were not genetically
closer to blue-winged warblers.

Additionally, the extent of yellow in hybrids re-captured in subsequent
years appeared to decline over time.

"Some researchers have hoped that the extent of yellow could indicate
how many generations a hybrid is removed from the parent species," said
David Toews, assistant professor of biology at Penn State and leader of
the research team.

"Our results indicate that it isn't quite so straightforward, and that classifying hybrids into groups based on the amount of yellow can be misleading." The inheritance of a black throat patch and face mask,
however, appears to be much more straightforward. The research team
previously identified a genetic region related to black coloration in
warblers. In the current study, the team used a rarer type of hybrid to
narrow that to a region about five times smaller.

"This one type of very rare hybrid looks almost entirely like a
blue-winged warbler, with a yellow body but with a black throat patch
and face mask, like a golden-winged warbler," said Baiz. "By comparing
its genome to that of blue- wing warblers, we were able to identify a
much smaller genetic region where the birds differed, which we believe
drives the black coloration." The genetic region is located near the Agouti-signaling protein (ASIP) gene, which is thought to regulate
production of the pigment melanin in some birds.

Next, the research team would like to confirm that this section of the
genome affects expression of the ASIP protein in warblers and underlies differences in their black plumage patches.

"We plan to continue to study the evolution of color across the 110
species of warblers, which have incredibly diverse plumage," said
Toews. "Now that we have identified a starting point, this narrowed down genetic region, we won't be stabbing in the dark." In addition to Baiz
and Toews, the research team includes Gunnar Kramer and Henry Streby from
the University of Toledo, Scott Taylor from the University of Colorado, Boulder, and Irby Lovette from the Cornell Lab of Ornithology. This
research was supported by the Cornell Lab of Ornithology, the
U.S. Geological Survey, and the National Science Foundation.


========================================================================== Story Source: Materials provided by Penn_State. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. David P L Toews, Irby J Lovette, Scott A Taylor, Henry M Streby,
Gunnar R
Kramer, Marcella D Baiz. Genomic and plumage variation in Vermivora
hybrids. The Auk, 2020; DOI: 10.1093/auk/ukaa027 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200714143040.htm

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