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Dear Neal,<br><br>
An interesting paper on Heliconius hybrids is now finally
"published". I get the feeling you only search this
journal sporadically, but thought you might like to know. By the
way, if you were going to choose it for "Science Sendings",
it'd be great if you didn't circulate the PDF (which is anyway not in
final nicely formatted form), but instead just circulated this website;
tbhe paper will always be freely available online. I think if lots
of your users clicked on the link it might get it into the highly cited
category. Anyway, I'd be keen to see.<br><br>
See:<br><br>
<b>Natural hybridization in heliconiine butterflies: the species boundary
as a continuum<br>
<a href="http://www.biomedcentral.com/1471-2148/7/28/" eudora="autourl">http://www.biomedcentral.com/1471-2148/7/28/</a><br>
James Mallet, Margarita Beltran, Walter Neukirchen, Mauricio
Linares<br>
</b><i>BMC Evolutionary Biology</i> 2007, <b>7</b>:28 (23Feb2007)
<br><br>
<br>
<font size=4>Background<br><br>
</font>To understand speciation and the maintenance of taxa as separate
entities, we need information about natural hybridization and gene flow
among species.<br><br>
<font size=4>Results<br><br>
</font>Interspecific hybrids occur regularly in Heliconius and Eueides
(Lepidoptera: Nymphalidae) in the wild: 26-29% of the species of
Heliconiina are involved, depending on species concept employed.
Hybridization is, however, rare on a per-individual basis. For one
well-studied case of species hybridizing in parapatric contact
(Heliconius erato and H. himera), phenotypically detectable hybrids form
around 10% of the population, but for species in sympatry hybrids usually
form less than 0.05% of individuals. There is a roughly exponential
decline with genetic distance in the numbers of natural hybrids in
collections, both between and within species, suggesting a simple
"exponential failure law" of compatibility as found in some
prokaryotes.<br><br>
<font size=4>Conclusions<br><br>
</font>Hybridization between species of Heliconius appears to be a
natural phenomenon; there is no evidence that it has been enhanced by
recent human habitat disturbance. In some well-studied cases,
backcrossing occurs in the field and fertile backcrosses have been
verified in insectaries, which indicates that introgression is likely,
and recent molecular work shows that alleles at some but not all loci are
exchanged between pairs of sympatric, hybridizing species. Molecular
clock dating suggests that gene exchange may continue for more than 3
million years after speciation. In addition, one species, H. heurippa,
appears to have formed as a result of hybrid speciation. Introgression
may often contribute to adaptive evolution as well as sometimes to
speciation itself, via hybrid speciation. Geographic races and species
that coexist in sympatry therefore form part of a continuum in terms of
hybridization rates or probability of gene flow. This finding concurs
with the view that processes leading to speciation are continuous, rather
than sudden, and that they are the same as those operating within
species, rather than requiring special punctuated effects or complete
allopatry. Although not qualitatively distinct from geographic races, nor
"real" in terms of phylogenetic species concepts or the
biological species concept, hybridizing species of Heliconius are stably
distinct in sympatry, and remain useful groups for predicting
morphological, ecological, behavioural and genetic characteristics.
<br><br>
<br><br>
<br>
All the best, Jim<br><br>
<x-sigsep><p></x-sigsep>
James Mallet<br>
<a href="http://www.ucl.ac.uk/taxome/jim/" eudora="autourl">http://www.ucl.ac.uk/taxome/jim/</a><br><br>
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