Re: DNA news stories: bird and mammal evolution

["Toby White" <mwhite@houston.rr.com>]

It could be the reverse just as easily.  I've beaten this issue to death
before, but a few quick points:

1) DNA phylogenetics is done on the basis of primary sequence data.  But
DNA functions either because of its own tertiary structure or the
tertiary/quaternary of the gene products for which it codes.  Unlike
morphological data, what you're looking at in sequence data is at least two
steps, maybe more, from the business end of selective pressures.

2) Unlike a lot of morphological studies, where you're not sure whether the
assumption of character independence is being violated, you know for
absolutely sure that its being violated in a DNA study based on one gene.

3) Even more than morphological characters, bits and pieces of genes get
shifted around and used in different ways at the same time.  To make a long
story short, we don't know whether we're looking at conservation of the
receptor gene here between grebes & flamingos, or looking at the
conservation of something else that, unique to grebes (or flamingos), just
happens to be linked to the sequence of the M6P/IGF2R gene.

Personally (i.e. tiny minority view) I'd like to see molecular
phylogenetics act more like morphological studies.  Forget the primary
sequence. Describe the similarities in the shape, charge distribution and
articulations of the ultimate gene products. Primary sequence studies are
like trying to compare the meaning of two paragraphs from a statistical
study of their use of the individual letters of the alphabet.

Go. The rant is ended.

--Toby White

The Vertebrate Notes at:
http://home.houston.rr.com/vnotes/index.html and
http://www.dinodata.net



----- Original Message -----
From: <bh480@scn.org>
To: <dinosaur@usc.edu>
Sent: Wednesday, July 04, 2001 6:22 AM
Subject: DNA news stories: bird and mammal evolution


> From: Ben Creisler bh480@scn.org
>
> DNA news stories: bird and mammal evolution
>
> A couple of recent news stories concerning evolution and
> DNA studies fall a bit outside the topic of dinosaurs
> strictly speaking but I think they are worth mentioning:
>
> DNA yields aquatic bird evolution surprise: flamingo and
> grebe are close relatives
> http://www.science.psu.edu/alert/Hedges7-2001.htm
>
> If this research holds up, it points out one of the main
> problems with cladistic analyses based solely
> on "characters" derived from skeletons -- apparent
> similarities or dramatic differences in body structure may
> be misleading in terms of true evolutionary histories. The
> many birdlike theropods or theropod-like birds that have
> been turning up lately provide an obvious case in point.
> Unfortunately without access to ancient DNA, the real
> story may remain unresolved.
>
> (Don't have the citation or abstract for the paper yet.)
>
> Mammal evolution theories confirmed and debunked:
> An article from Popular  Mechanics can be seen at:
> http://c.moreover.com/click/here.pl?l21352978
>
> The official abstract can be viewed at:
> http://link.springer.de/link/service/journals/00335/bibs/10
> 12007/10120513.html
>
> Killian, J. Keith , Thomas R. Buckley, Niall Stewart,
> Barry L. Munday, Randy L. Jirtle, 2001.
> Marsupials and Eutherians reunited: genetic evidence for
> the Theria hypothesis of mammalian evolution. Mammalian
> Genome. 12(7): 513-517
>
> Abstract
> The three living monophyletic divisions of Class Mammalia
> are the Prototheria (monotremes), Metatheria (marsupials),
> and Eutheria (`placental' mammals). Determining the sister
> relationships among these three groups is the most
> fundamental question in mammalian evolution. Phylogenetic
> comparison of these mammals by either anatomy or
> mitochondrial DNA has resulted in two conflicting
> hypotheses, Theria and Marsupionta, and has fueled a
> ``genes versus morphology'' controversy. We have cloned
> and analyzed a large nuclear gene, the mannose 6-
> phosphate/insulin-like growth factor II receptor
> (M6P/IGF2R), from representatives of all three mammalian
> groups, including platypus, echidna, opossum, wallaby,
> hedgehog, mouse, rat, rabbit, cow, pig, bat, tree shrew,
> colugo, ringtail lemur, and human. Statistical analysis of
> this nuclear gene unambiguously supports the morphology-
> based Theria hypothesis that excludes monotremes from a
> clade of marsupials and eutherians. The M6P/IGF2R was also
> able to resolve the finer structure of the eutherian
> mammalian family tree. In particular, our analyses support
> sister group relationships between lagomorphs and rodents,
> and between the primates and Dermoptera. Statistical
> support for the grouping of the hedgehog with Feruungulata
> and Chiroptera was also strong.
>
>
>