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<DIV class=article-heading><FONT size=4>Shark species more diverse than
thought</FONT></DIV></HGROUP>
<DIV>Genetic analysis suggests overlooked species, raises concerns about
conservation.</DIV>
<DIV><SPAN class=vcard><A class=fn
href="http://www.nature.com/news/shark-species-more-diverse-than-thought-1.10879?WT.ec_id=NEWS-20120626#auth-1">Daniel
Cressey</A></SPAN></DIV>
<DIV class=pubdate-and-corrections>Nature, 22 June 2012</DIV>
<DIV class=pubdate-and-corrections><A
href="http://www.nature.com/news/shark-species-more-diverse-than-thought-1.10879?WT.ec_id=NEWS-20120626">http://www.nature.com/news/shark-species-more-diverse-than-thought-1.10879?WT.ec_id=NEWS-20120626</A></DIV>
<DIV class=section></ASIDE>
<P class="content no-heading cleared main-content">A genetic study of thousands
of specimens of sharks and rays has uncovered scores of potential new species
and is fuelling biologists’ debates over the organisation of the family tree of
these animals. The work also raises the possibility that some species are even
more endangered than previously thought.</P>
<P class="content no-heading cleared main-content">Sharks and rays are key
predators in marine ecosystems, but the life cycles and population numbers of
many species remain poorly understood. The family tree of these animals — which
are part of the elasmobranch subclass — has proved similarly opaque, with little
agreement among researchers over their evolutionary relationships.</P>
<P class="content no-heading cleared main-content">Gavin Naylor, a biologist at
the College of Charleston in South Carolina, and his colleagues sequenced
samples from 4,283 specimens of sharks and rays as part of a major effort to
fill the gaps. The team found 574 species, of which 79 are potentially new, they
report in the <I>Bulletin of the American Museum of Natural History</I><SUP><A
id=ref-link-1 class=ref-link
title="Naylor, G. J. P. et al. B. Am. Mus. Nat. Hist. [vol], [page range][or link: http://dx.doi.org//xxxxx](2012)."
href="http://www.nature.com/news/shark-species-more-diverse-than-thought-1.10879?WT.ec_id=NEWS-20120626#b1">1</A></SUP>.</P>
<P class="content no-heading cleared main-content">Naylor says that he was
“flabbergasted” by the result, especially because the sequencing covered only
around half of the roughly 1,200 species thought to exist worldwide.</P>
<P class="content no-heading cleared main-content">The huge number of new
species found raises immediate conservation concerns — the reason that some of
these purported new species have gone undetected is probably their close
resemblance to already-identified species. The populations of such species may,
therefore, be even smaller than estimated, as what was thought to be one
population may instead be several smaller populations of separate species.</P>
<P class="content no-heading cleared main-content">For example, Naylor’s work
suggests that the endangered scalloped hammerhead (<I>Sphyrna lewini</I>) is
actually two separate species. “Scalloped hammerheads in general have taken a
huge hit, so it may be even worse than has been documented if there’s more than
one species out there,” he says.</P>
<P class="content no-heading cleared main-content">Naylor is now working on a
project with the US National Science Foundation to catalogue the diversity of
sharks and rays and is working to assist the International Union for
Conservation of Nature to map which species are where in the world.</P>
<P class="content no-heading cleared main-content">“This will have an impact on
what is considered endangered and the fragility of different organisms,” he
says. “These are sentinel species of all sorts of other organisms in the sea
which are probably undergoing similar or worse kinds of impacts.”</P>
<H2 class="content no-heading cleared main-content"><FONT size=2>Circling the
answer</FONT></H2>
<P class="content no-heading cleared main-content">One of Naylor’s
collaborators, William White, an ichthyologist at the Australian Commonwealth
Scientific and Industrial Research Organisation in Hobart, says that their work
also highlights some of the problems with the use of genetic information in
zoology.</P>
<P class="content no-heading cleared main-content">The increasing use of
molecular techniques provides a new means to scrutinize the relationship between
sharks and rays, he says. But it also shows that some of the existing ideas
about their relationships are problematic. “Part of the problem is some
researchers mining data blindly without a good understanding of where that data
has come from in the first place and presuming the names are correct which in
many cases they are not.”</P>
<P class="content no-heading cleared main-content">White and Naylor stress that
molecular techniques are only of one many available tools and should be combined
with conventional taxonomic work.</P>
<P class="content no-heading cleared main-content">Ximena Vélez-Zuazo is a
biologist at the University of Puerto Rico in San Juan and the lead author of a
2011 paper<SUP><A id=ref-link-2 class=ref-link
title="Vélez-Zuazo, X. & Agnarsson, I. Mol. Phylogenet. Evol. 58, 207–217 (2011)."
href="http://www.nature.com/news/shark-species-more-diverse-than-thought-1.10879?WT.ec_id=NEWS-20120626#b2">2</A></SUP>
that Naylor says suffers from some of the flaws that stem from relying solely on
molecular information. Though she strongly defends her group's work, she agrees
that shark phylogeny is still a work in progress.</P>
<P class="content no-heading cleared main-content">Vélez-Zuazo adds that most of
the debate centres on two of the eight living orders of sharks and rays. “The
main challenge for resolving the phylogeny for sharks remains the limited amount
of data,” she says.</P>
<P class="content no-heading cleared main-content">But both groups agree that
having a proper phylogeny of these animals is invaluable.</P>
<P class="content no-heading cleared main-content">“For an ancient and diverse
group like sharks, having a comprehensive phylogeny — meaning including the
majority of the more than 500 recognized species — will refine our current
understanding of fundamental aspects about the evolution of life history traits
of these animals, as well as bony fishes,” says Vélez-Zuazo.</P>
<DL class=citation>
<DT><A href="javascript:;" jQuery16404671790141965406="8"><FONT
color=#000000><STRONG>References</STRONG></FONT></A></DT></DL></DIV>
<DIV id=references class="section expanded">
<DIV class=content>
<OL class=references>
<LI id=b1>
<P><SPAN class="vcard author"><SPAN class=fn>Naylor, G. J. P.</SPAN></SPAN>
<I>et al</I>. B. Am. Mus. Nat. Hist. [vol], [page range][or link: <A
href="http://dx.doi.org//xxxxx](2012).">http://dx.doi.org//xxxxx](2012).</A></P><A
class="context-link show" href="javascript:;">Show context</A></LI>
<LI id=b2>
<P><SPAN class="vcard author"><SPAN class=fn>Vélez-Zuazo, X.</SPAN></SPAN>
& <SPAN class="vcard author"><SPAN class=fn>Agnarsson, I.</SPAN></SPAN>
<SPAN class=source-title>Mol. Phylogenet. Evol.</SPAN> <SPAN
class=volume>58</SPAN>, <SPAN class=start-page>207</SPAN>–<SPAN
class=end-page>217</SPAN> (<SPAN class=year>2011</SPAN>).</P></LI>
<UL class=ref-links>
<LI><A
href="http://dx.doi.org/10.1016/j.ympev.2010.11.018">Article</A> <A
href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=npg&cmd=Retrieve&db=PubMed&list_uids=21129490&dopt=Abstract">PubMed</A>
<A
href="http://links.isiglobalnet2.com/gateway/Gateway.cgi?amp;GWVerhttp://links.isiglobalnet2.com/gateway/Gateway.cgi?amp;GWVersion=2&SrcAuth=Nature&SrcApp=Nature&DestLinkType=FullRecord&KeyUT=000287888700007&DestApp=WOS_CPL">ISI</A>
<A class="context-link show" href="javascript:;">Show
context</A></LI></UL></OL></DIV></DIV></SECTION><SECTION>
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