Received: by alpheratz.cpm.aca.mmu.ac.uk id DAA01349 (8.6.9/5.3[ref pg@gmsl.co.uk] for cpm.aca.mmu.ac.uk from fmb-majordomo@mmu.ac.uk); Fri, 19 Jan 2001 03:59:46 GMT Subject: Fwd: Now They're Singing a Different Song Date: Thu, 18 Jan 2001 22:56:54 -0500 x-sender: wsmith1@camail2.harvard.edu x-mailer: Claris Emailer 2.0v3, Claritas Est Veritas From: "Wade T.Smith" <wade_smith@harvard.edu> To: "Memetics Discussion List" <memetics@mmu.ac.uk> Content-Type: text/plain; charset="US-ASCII" Message-ID: <20010119035512.AAA4496@camailp.harvard.edu@[204.96.32.110]> Sender: fmb-majordomo@mmu.ac.uk Precedence: bulk Reply-To: memetics@mmu.ac.uk
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From the BBC at:
<http://news.bbc.co.uk/hi/english/sci/tech/newsid_1123000/1123973.stm>
Songbird shows how evolution works
By BBC News Online science editor Dr David Whitehouse
Scientists may be witnessing one of the fundamental forces of evolution:
the
divergence of one species into two.
One of the largest mysteries remaining in evolutionary biology is exactly
how one species can gradually diverge into two
Darren Irwin, UCSD
It is the evidence that the originator of the theory of evolution, Charles
Darwin, wanted to see but was never able to find.
The new data comes from the songs of the greenish warbler, a bird that
lives
in the foothills of the Himalayas. Researchers have noticed that its song
changes gradually throughout its territory.
At the extreme ranges of its habitat, the greenish warbler will sing very
different songs. This means that although the birds belong to the same
species, they will not mate. And eventually, they will become two separate
species
One becomes two
Biologists are saying that this shows how one species can become two, a
process known as speciation.
"One of the largest mysteries remaining in evolutionary biology is exactly
how one species can gradually diverge into two," says Darren Irwin of the
University of California, San Diego, US.
The Himalayan warblers are an example of a rare condition known as a "ring
species".
"Ring species are unique because they present all levels of variation,
from
small differences between neighbouring populations to species-level
differences in a single group of organisms," says Irwin.
Defending territories
The greenish warbler (Phylloscopus trochiloides) lives in a ring-shaped
region around the Himalayas with gradually changing behavioural and
genetic
characteristics. The ring is broken in one place, in central Siberia,
where
two forms of the songbird exist.
"This creates a paradox in which two co-existing forms of the songbird can
be considered as two species and as a single species at the same time,"
remarks Irwin.
"Ring species are valuable because they can show all of the intermediate
steps that occur during the divergence of one species into two. In the
greenish warbler, as in most songbirds, males sing to attract mates and to
defend territories.
"The greenish warblers living in the Himalayas sing songs that are simple,
short and repetitive. As you go north along the western side of Tibet,
moving through central Asia, the songs become longer and more complex,"
says
Irwin.
Recorded songs
Irwin and his co-researchers publish their study of the bird in the
journal
Nature.
In their paper, they describe how when recordings of songs were played to
warblers which sang differently, the birds did not recognise them - and so
would not breed.
"The greenish warbler is the first case in which we can see all the steps
that occurred in the behavioural divergence of two species from their
common
ancestor," says Irwin.
"These results demonstrate how small evolutionary changes can lead to
differences that cause reproductive isolation between species, just as
Darwin envisioned."
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