Barn swallows dont
just live next to us theyre probably alive today because
of us.
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Image
credits Geograph Britain and Ireland.
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New research from the
University of Colorado Boulder reveals that barn swallows (Hirundo
rustica) a species of bird that likes to live in bridges
and sheds around the world might be more intertwined with
to us than previously thought. The paper explains that the barn
swallow and its subspecies likely evolved alongside humans, as we
were building our first settlements.
Neighbours with
benefits
Humans could
be a really big part of the story, said Rebecca Safran,
associate professor of ecology and evolutionary biology at CU
Boulder and paper co-author.
Theres very
few studies that can point to the exact influence of humans, and
so here, this coincidence of human expansion and permanent settlement
and the expansion of a group that relies really, really heavily
on humans is compelling.
Barn swallows are found
throughout the northern
hemisphere. They build mud-cup nests almost exclusively on human
structures. Other than the fact that they originate in northern
Africa, and that there are six barn swallow subspecies which
are have marked physical and behavioral differences we dont
really know much about their evolution. Previous research suggested
that the different subspecies split early, well before human settlement.
The new study gave the
issue a fresh look by analyzing the full genomes of 168 barn swallows.
Individuals were selected from the two subspecies
farthest apart on an evolutionary scale: H. r. savignii in Egypt
(a non-migratory species that lives along the Nile) and H. r. erythrogaster
in North America (a species found throughout North America that
migrates seasonally to South America). The team employed more sophisticated
computational resources and methods than were available for previous
studies. This gave them a more complete picture of barn swallow
speciation over time (i.e., when the subspecies separated). Their
results suggest the process happened much closer to the point in
time when humans began to build structures and settlements.
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Image
credits National Park Service.
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The previous
studies were playing with the idea of potential impact on population
sizes due to humans, said Chris Smith, a graduate student
in EBIO and the Interdisciplinary Quantitative Biology program,
and the studys lead author. Our results suggest
a much more substantial link with humans.
The findings still
preliminary also suggest that the evolutionary link between
humans and barn swallows was struck through a founder event
a situation which occurs when a small number of individuals
is able to take over a new environment quickly due to abundant resources
and an absence of competitors. For the swallows, the founder event
may have occurred as they moved into a new, relatively empty environment:
human
settlements.
Everyone is
always wondering how do you study speciation? Its been
viewed as this long-term, million-year (process), but in barn
swallows, we are not talking about differentiation within several
thousands of years, said Safran. Things are really
unfolding rather rapidly.
The paper Demographic
inference in barn swallows using whole-genome data shows signal
for bottleneck and subspecies differentiation during the Holocene
has been published
in the journal Molecular Ecology.
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