Endangered songbird challenging assumptions about evolution

Date:
March 30, 2021
Source:
University of Colorado at Boulder
Summary:
New research looked at a newly discovered, endangered songbird
located only in South America -- the Ibera' Seedeater -- and found
that this bird followed a very rare evolutionary path to come into
existence at a much faster pace than the grand majority of species.



FULL STORY ==========================================================================
Not all species may travel the same path to existence, at least according
to new findings from the University of Colorado Boulder and collaborators.


==========================================================================
This new research, out now in Science, looked at a newly discovered,
endangered songbird located only in South America -- the Ibera' Seedeater
-- and found that this bird followed a very rare evolutionary path to come
into existence at a much faster pace than the grand majority of species.

By comparing this bird to a closely related neighbor (the Tawny-Bellied Seedeater) in the same group (the southern capuchino seedeaters), the researchers determined that genetic shuffling of existing variations,
rather than new random mutations, brought this species into existence --
and their own behaviors are keeping them apart.

This species is one of only two known examples across the globe to
have traveled this path, challenging the typical assumptions of how new
species form.

"One of the aspects of this paper that makes it so cool is that we were
able to address this question of how the Ibera' Seedeaters formed from
multiple different perspectives," said Sheela Turbek, a graduate student
in ecology and evolutionary biology (EBIO) at University of Colorado
Boulder and the study's lead author.

"Not only did we collect on-the-ground data on who mated with one another
and the identity of their offspring, but we also generated genomic data
to examine how similar these two species are on a genetic level. We
then zoomed out further to look at where the Ibera' Seedeater fits in
the context of the broader capuchino group." "Many studies will address
one of these aspects or questions but not combine all of these different
pieces of information into a single study."


==========================================================================
The southern capuchino seedeaters are a group of recently evolved
songbirds found throughout South America that is branching rapidly, with
many of its species in the early stages of evolution. This family is
best known for the dramatic variation with the males in terms of songs
and plumage color, while the females are largely indistinguishable even
to the most familiar researchers.

The Ibera' Seedeater, the most recent member of this family, was first discovered in the remote, swampy grasslands of Ibera' National Park in
northern Argentina by study co-authors Adria'n S. Di Giacomo and Cecilia Kopuchian from Centro de Ecologi'a Aplicada del Litoral, Argentina,
in 2001, and then described in scientific literature in 2016.

In that national park, though, are six other closely related species of capuchinos, including the Tawny-Bellied Seedeater, that breed closely
beside each other. These species, despite occupying the same environment
and eating the same food, rarely interbreed.

And so, researchers wondered why -- and how -- the Ibera' Seedeater even
came to be.

They explored these questions in two ways: First, they looked at how
this new species may have formed by examining the ways in which its DNA
differs from the Tawny-Bellied Seedeater, and second, looking at what mechanisms might be preventing it from interbreeding with the other
species that occur in the park.



==========================================================================
To do that, Turbek went down to Argentina for the breeding season
for three years, staying two and a half to three months at a time,
searching for and monitoring nests, collecting blood samples from adults
and nestlings, and then, in the final year, performed a behavioral
experiment to see whether plumage or song played a roll in terms of
species recognition.

"The field work involved in collecting the assortative mating and
behavioral data is extraordinarily hard, which is why these kinds
of datasets rarely exist. This study and publication are a testament
to Sheela's skill and hard work in the field," said Scott Taylor, an
assistant professor in EBIO at University of Colorado Boulder, an author
on the paper and Turbek's advisor.

What they found is that the two birds are closely related genetically,
only distinguishable by the genes involved in plumage coloration. As
well, they found that the males responded most aggressively to songs
and plumage variations aligning with their own species.

This all means that the species could very well reproduce and hybridize
-- they just choose not to, therefore reinforcing their own reproductive barriers.

On a broader level, though, when comparing the Ibera' Seedeater to other capuchino species, the researchers found that the Ibera' Seedeater shares genomic variants with other capuchinos in these regions, but the variants
have been shuffled to form a unique combination, which, the researchers
argue, could be an evolutionary shortcut that most likely underlies much
of the diversity among the different subspecies of this family.

"This is a really beautiful story about a process that we have never seen
in quite this way before," says co-author Irby Lovette, director of the
Fuller Evolutionary Biology Program at the Cornell Lab of Ornithology.

"The classic and most common evolutionary model for new species is the accumulation of genetic mutations when those species are separated by
a geographic barrier over perhaps millions of years. But here we found
that genetic shuffling can happen quickly and without geographical
isolation. It's almost like 'instant speciation.'" Leonardo Campagna,
a research associate at the Cornell Lab of Ornithology and the senior
author on the paper, agrees: "This is the clearest example in birds of
how reshuffling of genetic variation can generate a brand-new species."
The only other organism where this type of evolution has been seen,
according to Turbek, is a group of fish found in Africa called the Lake Victoria cichlids.

"It's interesting to see this mechanism operating in something as
different as birds," Turbek commented.

While this study focused in part on the role of male behaviors, the
researchers are very interested in taking it one step further, examining
the role that female choice may also play in reproduction.

"There are many more questions that we have to address," Turbek said.

========================================================================== Story Source: Materials provided by
University_of_Colorado_at_Boulder. Original written by Cay
Leytham-Powell. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sheela P. Turbek, Melanie Browne, Adria'n S. Di Giacomo, Cecilia
Kopuchian, Wesley M. Hochachka, Cecilia Estalles, Dari'o
A. Lijtmaer, Pablo L. Tubaro, Lui's Fa'bio Silveira, Irby
J. Lovette, Rebecca J.

Safran, Scott A. Taylor, Leonardo Campagna. Rapid speciation via the
evolution of pre-mating isolation in the Ibera' Seedeater. Science,
2021; 371 (6536): eabc0256 DOI: 10.1126/science.abc0256 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/03/210330171034.htm

--- up 5 days, 8 hours, 39 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)