Re: Re: DNA sequencing (long)

Jan Schlauer (
Tue, 3 Oct 1995 11:15:42 +0100

Dear DNAists,

>>only suggest that _Roridula_ belongs to a huge and probably heterogeneous
>> complex of many loosely related families (something like Corniflorae) of
>> low-intermediate "advancedness" (if something like this does exists), the
>> Sarraceniaceae being (+/-) associated to the same clump but very probably
>> from a rather radically different end.
>So it's more like a 2nd cousin type of relationship? ;)


Oh, BTW, I have an addendum on further reading for DNA fans:

CONRAN (yes, the same who described _Byblis liniflora subsp.occidentalis_
together with Allen LOWRIE) & DOWD
"The Phylogenetic Relationships of _Byblis_ & _Roridula_ Inferred from
Partial 18S Ribosomal RNA Sequences", Pl.Syst.Evol.118:73-86 (1993), I
guess you will like it, Fernando: they are using your favourite sequence.

The last paper was the reason in my previous letter to state that
Byblidaceae were closer to Solaniflorae than to Lamiiflorae. However, I see
now that they have not examined a single member of Lamiiflorae, so I wish
to correct my former statement: just forget it, the evidence to support it
is less than weak (sorry; inexcusable).

>I thought Fernando was emphasizing the relationships with regard to
>CP and meant that Drosera closer to Nepenthes than other CP. Did I
>get that right? Jan, are you saying that is wrong?

It *may* be sort of wrong: if _Triphyophyllum_ took (please note that I am
not stating this to be so without doubt) an intermediate position between
the two families, the statement "Drosera closer to Nepenthes than other CP"
will obviously become oversimplified (which is "wrong" sensu stricto).

> I'm not sure but
>it seems you guys aren't "on the same wavelength" so to speak.

This is a wrong impression. In fact, I think we are pretty much on the same
wavelength, but I think I should emphasize some points which need
clarification. These points are the reasons for most errors and
misconceptions in contemporary systematic literature (and I really dislike
to read nonsense).

>Yeah, it isn't hard to reach that conclusion without the DNA testing
>but wouldn't this lend support to the validity of this type of comparison?

I would formulate it the other way round: this type of comparison lends
support to the conclusions from comparative morphology. All other
implications are at least dangerous.

>Jan, perhaps gemmae are not really that big of a jump. Has anyone
>studied the gemmae to see what part grows into the new plant? Does
>the area close to where the petiole is/would be grow like a D.petolaris
>cutting or does the entire gemmae sort fold out into a new plant? If
>it's the latter case, I would think that indicates a more remote rela-

The gemmae include small "embryoids" like seed. These grow out into new

BTW, as you may have noticed, I listed a whole catalog of differences, not
only gemmae formation.

>Oh, what is meant by 'caryological' the dictionary here is of
>no help.

It means chromosome numbers and morphology.

>>I am not as enthusiastic as you about "modern molecular methods" (in fact,
>>I cannot support any "monotheistic" approach to systematics).
> I don't know what you meant by "monotheistic approaches to
>systematics" (what God has to do with systematics is a whole other line of
>discussion), but if you mean roughly "don't put all your eggs in one
>basket" I agree.

This does rather aptly describe what I was trying to say.

> Sequencing of one gene gives you the divergence pattern
>of that gene which isn't necessarily the same as that for the organisms
>involved. As with all science, accumulating independent lines of evidence
>is the best approach for discerning "true" patterns of nature. I might add
>that sequencing, even of different genes, is just one molecular
>phylogenetic technique. There is protein electrophoresis and RFLPs just to
>name two.

This is also my opinion.

>Depending on what questions one is asking, molecular techniques
>may be an extremely important, if not the only way, to get appropriate

I am perhaps a little bit more sceptical in this respect.

>>This is rather exactly the kind of short-sighted implications which are the
>>greatest danger of "modern molecular methods".
> The gene tree in the Albert et al. 1992 that Fernando was writing
>about may have its limitations, but this dataset yields as valid an
>estimate of phylogeny as any other character based analysis (and better
>than many).

No. This is the point I want to stress: as it is based on a single DNA
sequence only, it is highly inferior to combined analyses even of purely
morphological characters. Yes, I know the argument that every single base
in a sequence is a morphological character, but this is not exactly true.
The limitations of purely genetical analyzes have been discussed in some
detail (also by yourself) already. This is what I call a monotheistic
approach, and "DNAism" is frequently too dogmatic and short-sighted in this

>I think the main point of the paper is still fascinating:
> Nothing "short-sighted" about it.

The close relationship between Roridulaceae and Sarraceniaceae is, as I
think, one example of a short-sighted implication from this tree (very well
comparable to my own short-sighted association between Byblidaceae and
Solaniflorae, shame on me!). Moreover, to put "Caryophyllids" close to
Nepenthaceae or Droseraceae contradicts so many morphological and
phytochemical characters that it seems highly unlikely from a phylogenetic
point of view.

Again, I am not stating that sequence comparison or other molecular
techniques are not suitable for systematic research (especially for
confirmation of other results), but it is wrong to think that a tree
constructed from *one sequence alone* will be better than a thorough
examination, evaluation, and comparison of *all* available (morphological,
ecological, chorological, *and* molecular) characters. My warning: Do not
oversimplify, and do not forget the organisms!

Kind regards