return to main index

  mobile - desktop
follow us on facebook follow us on twitter follow us on YouTube link to us on LinkedIn
 
Click here for LLL Reptile & Supply
Mice, Rats, Rabbits, Chicks, Quail
Available Now at RodentPro.com!
Locate a business by name: click to list your business
search the classifieds. buy an account
events by zip code list an event
Search the forums             Search in:
News & Events: Herp Photo of the Day: False Coral Snake . . . . . . . . . .  Herp Photo of the Day: Bearded Dragon . . . . . . . . . .  Greater Cincinnati Herp Society Meeting - Apr 02, 2024 . . . . . . . . . .  Calusa Herp Society Meeting - Apr 04, 2024 . . . . . . . . . .  Southwestern Herp Society Meeting - Apr 06, 2024 . . . . . . . . . .  Hamburg Reptile Show - Apr. 13, 2024 . . . . . . . . . .  St. Louis Herpetological Society - Apr 14, 2024 . . . . . . . . . .  San Diego Herp Society Meeting - Apr 16, 2024 . . . . . . . . . .  Suncoast Herp Society Meeting - Apr 20, 2024 . . . . . . . . . .  DFW Herp Society Meeting - Apr 20, 2024 . . . . . . . . . .  Colorado Herp Society Meeting - Apr 20, 2024 . . . . . . . . . .  Chicago Herpetological Society Meeting - Apr 21, 2024 . . . . . . . . . . 
Southwestern Center for Herpetological Research
full banner - advertise here .50¢/1000 views
Layne Labs - Natural Diets for Pets & Wildlife
pool banner - $50 year

RE: another try: Sibling species...

[ Login ] [ User Prefs ] [ Search Forums ] [ Back to Main Page ] [ Back to Taxonomy Discussion ] [ Reply To This Message ]
[ Register to Post ]

Posted by: aspidoscelis at Fri Sep 2 13:39:46 2005  [ Report Abuse ] [ Email Message ] [ Show All Posts by aspidoscelis ]  
   

"Previously, you seemed to regard the genetic part as an optional extra..."

I was being facetious to some extent. Although, if you have fixed morphological differences that aren't just the result of plasticity, you necessarily have genetic differentiation as well.

"That's not quite true. In his Herpetol. Monogr. paper, he did show that the pattern of variation in overall morphology correspodned more closely to the mtDNA haplotype clades than to the conventional subspecies. That in itself does not demonstrate species status, but does suggest that the historical lineages do have relevance beyond just the mtDNA molecule."

Yes, his mtDNA clades correspond better with scale measurements than do the traditional subspecies, but he does not demonstrate that the variation is anything other than clinal. He could apply the same techniques to arbitrary sections of a cline and get the same results.

"I would disagree - it simply says that two long-standing independent lineages have not evolved differences in those characters we have looked at. Since there are molecular differences (and if they have been independent for a long time, then other molecular markers will also be affected), I would not regard that as a distinction "without a difference"."

Suppose you have two clades with divergent sequences in a gene that still codes for exactly the same protein with exactly the same functionality. What's the difference? It's like calling "behavior" and "behaviour" different words because they're spelled differently. The letters are important only in so far as they convey information, and the same is true for nucleotides.

"True, but one could also regard that as a strength - I recall hearing (sorry, don't have a ref for that) that some alleles have not reached coalescence between humans and chimps... the view that we are the same species would pobably be a minority opinion..."

Then again, the main reason why we would be very reluctant to view humans and chimps as conspecific is that there is such abundant morphological, developmental, etc., differentiation.

>>"Which takes us back to an extreme typological species concept that would elevate every mildly differentiated lizard population on a different rock outcrop in a sea somewhere as a different species - not always very convincing, and not really what many people are doing."

"That is the sort of compromise I can live with, and, I suspect, that many people follow as a gut instinct. As a herp example, I fully agree with Scott Keogh's sinking of the various Notechis scutatus/ater subspecies, which differ mostly in body size but are minimally differentiated genetically, just as, on the other hand, I haveno problem with recognising Bothrops insularis as a species, despite the fact that, in terms of mtDNA, it is rooted within Bothrops jararaca - it is just too different and not the same snake."

Agreed.

>>But extended separation does not demonstrate lack of future reintegration,

"And yet, in a previous post, you wrote:
"my feeling is simply that systematists must deal with current reality rather than trying to read the future"."

Yes. If you've got mtDNA clades that might reintegrate or might not, you've got to guess the future in order to come to the conclusion that they do, in fact, represent diverging lineages. OTOH, if you've got evidence that they have already undergone divergent evolution then you don't have to make that kind of guess.

>>"If one subscribes to the fundamental notion that species are best defined as independently evolving lineages, then I would have thought that evidence of differentiation at the molecular level would be just as relevant as morphological differences (with the caveat that mtDNA cannot test for paternal gene flow between contiguously distributed populations)."

"I guess we just differ as to what markers we accept as indicators of differentiation - I'd go with profound genetic divergences alone, you would not."

Yup.

If the differences are really, really strong they alone might be enough. But the genetic sequences most useful for phylogenetic reconstruction are those either not under selection or under constant, stable selection for conserved protein function. They're most useful when they provide the least information about evolutionary divergence, when they either have no impact on phenotype or have the same impact on phenotype throughout the study taxa.

I guess my basic feeling is that the organism is the phenotype. The genotype is important in so far as it causes the phenotype, but has no inherent importance to me; without the phenotype, it's just chemistry rather than biology...

"I'd like to carry on this discussion, which has been interesting, but since I am away for the next month, I will have to take a rain check on that. Anyhow, it's been fun."

I've been enjoying it, too. Perhaps we'll continue later.

Patrick Alexander


   

[ Reply To This Message ] [ Subscribe to this Thread ] [ Show Entire Thread ]


<< Previous Message:  RE: another try: Sibling species... - WW, Fri Sep 2 10:54:59 2005