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<DIV><A
title="Permanent Link to Pyura chilensis: the closest thing to getting blood from a stone"
href="http://blogs.scientificamerican.com/running-ponies/2012/06/21/pyura-chilensis-the-closest-thing-to-getting-blood-from-a-stone/"
rel=bookmark target=_blank><FONT color=#000000 size=4 face=Arial>Pyura
chilensis: the closest thing to getting blood from a stone</FONT></A></DIV>
<DIV><SPAN><FONT size=2 face=Arial>By </FONT><A><FONT size=2 face=Arial>Becky
Crew</FONT></A></SPAN></DIV>
<DIV><SPAN><FONT face=Arial><FONT size=2><SPAN>January 07,
2012</SPAN></FONT></FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial><FONT size=2><SPAN><A
href="http://metaphnora-awakening.blogspot.com/2012/07/pyura-chilensis-closest-thing-to.html">http://metaphnora-awakening.blogspot.com/2012/07/pyura-chilensis-closest-thing-to.html</A></SPAN></FONT></FONT></SPAN></DIV>
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<P style="FONT: 13px/13px ApresTT,Prelude,arial,sans-serif"><IMG
title=Pyura_chilensis alt=""
src="http://www.chilereisen.at/Chile/Pyura_chilensis.jpg" width=609
height=465></P>
<DIV>
<P align=center>****</P>
<P>Despite appearances, this is not some kind of cruelly bisected alien stone
organism or a tomato thunderegg. This is <I>Pyura chilensis</I>, a sea creature
that lives on the rocky coast of Chile and Peru. And if (like me, very recently)
you’ve never seen one of these before, you’ll probably be interested to know
that in Chile, they are fished commercially, and the locals eat them raw or
cooked with salad and rice because apparently they’re delicious.</P>
<P><I>P. chilensis </I>belongs to the Ascidiacea class of non-moving, sac-like
marine invertebrate filter feeders that are otherwise known as sea squirts. They
belong to the Tunicata subphylum, so-called because they wear thick ‘tunics’
made of tunicin, which is a hardy matrix of molecules that help the animal
attach itself to a hard surface on which it will carry out its days. The insides
of this tunic are lined with an epidermis and a muscular band, and inside these
layers lies the main part of the animal.</P>
<P><I>P. chilensis </I>has two siphons that connect the animal to the
surrounding ocean through its tunicin – one for exhaling and one for inhaling.
It eats by inhaling the water and filtering out the edible microalgae using a
moving layer of mucus in its enlarged pharynx, or branchial sac, before exhaling
the water back out the other siphon. The pharynx is connected to the animal’s
digestive tract, which basically acts like a mouth.</P>
<P>Their blood is clear and, strangely, can accumulte extremely high qualities
of a mysterious and rare element called vanadium. The concentration of vanadium
in the blood of<I> P. chilensis </I>and other tunicates can be up to 10 million
times that of the surrounding seawater. Just why and how these creatures are
able to accumulate vanadium in such huge quantities remains unknown.</P>
<DIV style="WIDTH: 321px"><IMG title=piure_Valaparaiso alt=""
src="http://upload.wikimedia.org/wikipedia/commons/7/7c/Piure_Valaparaiso.JPG?uselang=es"
width=311 height=233>
<P><FONT size=1>A Pyura chilensis dish from a market in Valparaiso in
Chile</FONT></P></DIV>
<P><I>P. chilensis </I>can often be found in densely packed aggregations of
thousands or small handfuls of just a few, or they can be found on their own –
in which case they must reproduce on their own, as there is no way of them
moving to find a mate. This means <I>P. chilensis </I>is hermaphroditic, with
the gonads of both a male and a female that can release eggs and sperm
simulataneouly to meet as a fertile cloud in the surrounding water. If the
sperm-egg collisions are successful, they will produce tiny tadpole-like
offspring that will eventually settle onto a rock to grow into the adult
form.</P>
<P>In 2005, biologists Patricio H. Manríquez from the Universidad Austral de
Chile and Juan Carlos Castilla from the Pontificia Universidad Católica de Chile
<A href="http://www.int-res.com/abstracts/meps/v305/p113-125/"
target=_blank>published a paper</A> in the <I>Marine Ecology Progress Series</I>
revealing for the first time the particulars of this creature’s reproductive
habits (They also use the verb ‘selfing’ often and with glorious earnestness).
They collected 30 sexually mature <I>P. chilensis </I>from habits in central and
northern Chile and set them up in lab tanks as isolated and paired individuals.
They wanted to assess the occurrence and success of fertilisation via these two
types of reproduction followed by the settlement of the resulting offspring to a
hard surface and their subsequent metamorphosis into adulthood.</P>
<P>First, the isolated individuals were placed in plastic bottles, and were left
alone for 90 days, free to do all the selfing they wanted (YOLO). After this
period, their body size relative to the amount of sperm in the water was
measured for each spawning episode. Next, the researchers combined pairs either
from the same population, or from two different populations, to see how well
they would breed in comparison to the selfers. A third experiment saw them keep
<I>P. chilensis</I> individuals in isolation for one to 16 months, to see if an
extended period alone would improve the success of selfing. Finally, the
researchers conducted ‘manipulated ferilisation’, which involved removing eggs
from the specimens and fertilising them with extracted sperm in Petri
dishes.</P>
<P>The results showed that <I>P. chilensis </I>is born male, before becoming
cosexual – having both male and female gonads – in its adolescence as it
increased in size. The researchers also found that given the choice – that is,
if situated around other individuals – these organisms prefer to breed via
cross-fertilisation, writing, “Given that more events of natural egg spawning
followed by successful settlement and metamorphosis were recorded in our paired
specimens and in our manipulated cross trials … it appears that
cross-fertilisation predominates in this species.”</P>
<P>Manríquez and Castilla also found that a greater number of fertilised eggs
resulted from the paired specimens, which suggests that cross-fertilisation, or
reproducing with another individual, predominates because it is more effective.
This assumption was strengthened by the fact that individuals that had
cross-fertilised before being put in isolation took at least two months before
successfully producing offspring via selfing. However, they were careful to note
that while cross-fertilisation was preferred, selfing did not produce inferior
offspring. “No perceptible differences in fertilisation, settlement and
metamorphosis success among self and outcross progeny were found,” they
reported. This suggests that when stuck alone in the ocean, selfing provides an
advantageous opportunity for loner <I>P. chilensis </I>individuals to still pass
on their genes.</P>
<P><A href="http://www.youtube.com/watch?v=Ot-_xTDJgVI" target=_blank>Here’s a
video</A> of a German man knifing some <I>P. chilensis</I> with great aplomb to
the tune of a handful of angry YouTube
villagers.<I><BR></I></P></DIV></DIV><SPAN><IMG alt="Becky Crew"
src="http://blogs.scientificamerican.com/wp-content/uploads/userphoto/443.thumbnail.jpg"
width=60 height=54></SPAN><B>About the Author:</B> Becky Crew is a Sydney-based
science writer, award-winning blogger and former online science editor. She is
the author of 'Zombie Tits, Astronaut Fish and Other Weird Animals' (due
late-2012, UNSW Press). Follow on Twitter <A href="http://twitter.com/BecCrew"
target=_blank>@BecCrew</A>.
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