[Taxacom] Paraphyletic species: Crocodylus niloticus

[John Grehan]

Dan,

Thanks for the paraphyly explanation as I had not seen the original article and it was not covered in the link given by Ken. I have no particular view on that proposed relationship other than having doubts about whether mtDNA can show anything more than variation related to metabolic adaptation. 

On dispersal, I presume you have seen Head's comments and that you can now understand how this example of phylogenetic evidence combined with the interpretation of available fossil records does not constitute a convincing case of transatlantic dispersal.

John Grehan

-----Original Message-----
From: Dan Lahr [mailto:daniel.lahr at gmail.com] 
Sent: Friday, May 13, 2011 4:58 PM
To: John Grehan
Cc: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Paraphyletic species: Crocodylus niloticus

Hi John,

Paraphyly: The article suggests that C. niloticus is paraphyletic because eastern and western populations constitute independent lineages in their reconstructions: eastern populations are more closely related to New World species than to western populations. It is only an indication of paraphyly as the reconstruction is based on mitochondrial genes.  These are maternally inherited, thus an alternative hypothesis may be coined that females stay more at home than males (one can look at nuclear genes to test this hypothesis).
It is also worth noting that 6 specimens hardly constitutes comprehensive sampling to definitively conclude paraphyly of the species, in my view this is more of a particularly striking piece of evidence.

DIspersal: The oldest C. niloticus fossils are Pliocene, and the oldest New World Croc fossils are also Pliocene. Because the branching pattern revealed by this study puts C. niloticus + NW crocs in a well-supported clade, one can only conclude that a C. niloticus traveled from Africa to NW in the Pliocene, i.e. around 3.6 Mya. No molecular clock needed, and in fact the authors did not use any implementation of molecular clocks in their analyses.

I do not understand how this example of phylogenetic evidence combined with the interpretation of available fossil records does not constitute a convincing case of transatlantic dispersal.

Kind regards,

Dan

On Fri, May 13, 2011 at 4:16 PM, John Grehan <jgrehan at sciencebuff.org> wrote:
> It's not an example of transoceanic dispersal at all. That's just the 
> usual misrepresentation of molecular clock dates as actual or maximal.
>
> The article did not give any indication of paraphyly. Please describe.
>
> John Grehan
>
> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu
> [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth 
> Kinman
> Sent: Friday, May 13, 2011 4:03 PM
> To: taxacom at mailman.nhm.ku.edu
> Subject: [Taxacom] Paraphyletic species: Crocodylus niloticus
>
> Dear All,
>       A recent paper indicates that Crocodylus niloticus is 
> paraphyletic with respect to the clade of Crocodylus species in the 
> Americas.  Not only a great example of a paraphyletic species, but 
> also transoceanic dispersal as well.  Link to news story is given below.
>               ----------Ken
>
> http://www.newscientist.com/article/dn20464-crocodiles-swam-the-atlant
> ic
> -to-reach-america.html
>
>
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--
Daniel Lahr
-------------------------------------------------
PhD candidate
Organismic and Evolutionary Biology
U Massachusetts- Amherst
319 Morrill Science Center, Amherst
Amherst, MA 01003
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