[Taxacom] Neanderthals a species? (was: barcode of life)

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Fri Jul 2 22:33:12 CDT 2010


thanks Ken ... I think this supports my view

>These examples show how too many biologists still fail to recognize just how difficult speciation actually is and too often jump to the conclusion that differences (morphological, genetic, or even behavioral) indicate speciation RATHER than subspeciation

what they show is that the morphological species concept (i.e., any consistent morphological difference between (allopatric) populations is definitive of speciation) doesn't work (and it was never clear how to apply it sympatrically, anyway)

the BSC (which I favour) says that only morphological differences of sufficient magnitude to ensure high levels of reproductive integrity are relevant. If additional information shows that there are no (or low) barriers to interbreeding, then the hypothesis of distinct species in that case is refuted

similarly, molecular taxonomy is just a special case of the BSC which says that (in the absence of morphological differences) genomic differences of sufficient magnitude are indicative of reproductive isolation and therefore speciation

a tricky example from N.Z. is Geodorcus sororum Holloway, 2007, a flightless atag beetle restricted to the Sisters islets in the Chatham Islands. Is it, or isn't it conspecific with G. capito from the remaining islands in the group? Holloway initially thought so, but then changed her mind and described it as new. The problem is that apart from a slight size difference (on average), females are identical morphologically. Males are HUGELY different in external morphology and size, but have identical genitalia. No genetic differences have been found to justify the species distinction, but Holloway hypothesises that the external morphological differences between males are of sufficient magnitude to ensure reproductive integrity, and until such time as it is proven otherwise, she considers them to be distinct species. Although this example is particularly "tricky", I suggest that the basic rationale here is one we use all (or most) of the time when describing
 new species based on some or other differences between populations ...

Stephen




________________________________
From: Kenneth Kinman <kennethkinman at webtv.net>
To: taxacom at mailman.nhm.ku.edu
Sent: Sat, 3 July, 2010 3:09:55 PM
Subject: [Taxacom] Neanderthals a species? (was: barcode of life)

Hi Stephen and others:      
          There are quite a number of examples of two populations being
the same species and yet they not only can show distinctive differences,
but they can also become sympatric and fail to interbreed (particularly
the far ends of a circle of subspecies).  But these are relatively
unusual occurences that are often (but not always) different from a
cryptic species, so that is apparently not the type of example for which
you are looking.        
        However, within our own genus of Homo, there are two fairly
good examples.  One is Homo neanderthalensis, often considered a
separate species, but which I have always classified as Homo sapiens
neanderthalensis.  New genomic analyses a few months ago indicated that
Neanderthals did indeed interbreed with Homo sapiens (with some living
populations still containing 1-4% of Neanderthal genes).  They clearly
interbred with us, and should be classified as a subspecies, Homo
sapiens neanderthalensis.            
        Then there is Homo floresiensis (the "hobbit"), often claimed
to be a separate species.  Although I certainly agree that it is NOT a
diseased Homo sapiens (microcephalic or otherwise), I also cannot agree
that it is a separate species.  I still believe it is best classified as
a subspecies of either Homo erectus (a view which I still lean towards)
or a subspecies of Homo habilis.      
      These examples show how too many biologists still fail to
recognize just how difficult speciation actually is and too often jump
to the conclusion that differences (morphological, genetic, or even
behavioral) indicate speciation RATHER than subspeciation.        
            --------Ken Kinman      
P.S.  Going back to the circle of subspecies, I strongly suspect that
there are such circles of subspecies (or populations) in smaller
geographical areas which are actually morphologically indistinguishable
when they circle around and meet their ancestral population.  In that
case, morphology may be mainly unchanged, but fast evolving genes Iike
COI may have diverged to an extent that some  barcoders might consider
them specifically distinct.  What might surprise barcoders in such
instances, is that there can be a circle of populations outside that
limited area (such as Costa Rica) which are intermediate in their COI
sequences).  Therefore, so-called cryptic species can actually turn out
to be cryptic subspecies at the opposite ends of a cline which they have
not yet sampled.  Such problems are always a matter of limited sampling.
Until expanded sampling elsewhere demonstrates that intermediate
populations have gone extinct (often a dangerous assumption), it is just
a matter of a lack of information that merely suggests speciation where
it hasn't actually occurred (gene flow continues through those
intermediate populations).  In the case of the butterfly genus which I
discussed recently, COI sampling outside of Costa Rica (either north or
south of Costa Rica) could uncover such small circles of subspecies
circling back to Costa Rica.  This is just another reason that I
question Hebert et al.'s (2004) "Ten species in one" conclusions.
Barcoding (however useful it can be) is just another example in which
speciation can be exaggerated.  Single genes are simply not enough, and
barcoding should therefore not be limited to a single gene (at least one
nuclear gene, not a NUMT, should be used to bolster such conclusions
based on a single mitochondrial gene).
------------------------------------------------------------
Stephen Thorpe wrote:
      Please give me an example of two populations which are the same
species even though there are significant morphological (genitalic),
behavioural, and/or genetic differences of the order that is normally
taken to be indicative of reproductive isolation and therefore species
delimitation? If I understand them correctly, even the molecular
taxonomists are looking for genetic differences of sufficient magnitude
to indicate reproductive isolation - they just think that morphological
differences are only one of several ways that can lead to such
reproductive isolation ... 
Stephen


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