Cladistics and "Eclecticism"

[SKÁLA Zdenek]

From: Pierre Deleporte
>As a student of social 
>evolution, I could like to name a clade characterised by a synapomorphy in 
>this respect (social organisation type Y), ...
>Thus the number of changes in different characters is not the only possible 
>criterion, and characters of interest matter ...
>"Optimization" in this field depends on the centers of interests of the 
>users...

I fully agree. My point was that the rules for the taxa delimitation should be used (1) explicitly and (2) consistently within a project/paper to avoid miscomunication. Criteria based on number of character state transitions are only an example of such approach.

Z Skala:
>>I believe this is not true: let's imagine a pectinate cladogram of 
>> species A,B,C,D,E where clade A+B is supported by 5 synapomorphies, A+B+C 
>> by 2 syn., A+B+C+D by 10 syn. and the entire group by 12 syn. Eclecticist 
>> will split the cladogram into, say "genera" A+B, C+D and E and families 
>> A+B+C+D and E.

P Deleporte:
>You mean that two significant gaps are retained for naming: 
>5 changes and 10 changes.

Yes.

P Deleporte:
>Besides the trivial terminals and complete clade (ABCDE), note that 
>restituting complete phylogenetic information requires here 3 genera and 
>two families, thus 5 names,... etc.
Yes; however - as you correctly noted - taxa are not a tool of translating all cladogram contents into words but instead a way of summarizing of information included. The discussion is about the type of this summarizing process.

Z Skala:
>> Cladists, I believe, will use taxa A+B, C, D, E and more inclusive taxa 
>> A+B+C+D and A+B+C+D+E.

P Deleporte:
>You mean that they will possibly name only two clades (besides the trivial 
>five terminals and complete clade ABCDE), retaining 5 and 10 as significant 
>gaps.

Exactly.

Z Skala:
>>  As you can see, the number of taxa limits is the same or lower in the 
>> eclectic solution (limits B|C, D|E).

P Deleporte:
>I don't see at all that the number of limits is lower. It is 5 and 10 
>changes judged "significant gap for naming" in both cases (and besides this 
>cladistics clearly require fewer names in this case).

I had in mind the limit C|D that a cladist should use to provide taxa C and D rank of "genus" (i.e. eclectic genera A+B, C+D, E against cladistic A+B, C, D, E). But OK, let's think in the Phylocode manner not discussing the level of terminal taxa.

P Deleporte:
> I meant that additional 
>arbitrariness is introduced by the requirement of deciding "when to look at 
>phylogeny backwards", and not always "upwards" :
>The cladist has a unique criterion: clades. He(she) may add the criterion 
>"significant gaps" if he refuses to name all the clades.
-------End of decisions.--------
>Consequently, he names clades A+B (supported by 5 changes), and A+B+C+D 
>(supported by 10 changes).

>Now, the eclecticist has two incompatible criteria: clades, and possibly 
>grades. He may add "significant gaps" if he refuses to name all the clades 
>or grades. Here he decides to consider "more than 4 changes" as...

Perhaps there is some misunderstanding here: what do you mean by these "two criteria"? Do you mean the existence of grades? If I understand you well, the grades are paraphyletic taxa (below you mention "grade C+D"). If this is a case I should note that in the eclectic definition of monophyly there are no two criteria considered: monophyletic taxon is simply any connected subgraph of the cladogram (even despite it is oriented/rooted or not). Speaking in the graph theory, it is cladistic concept that is a bit more complicated - it rely on the descendant nodes and hence require oriented graphs. However, I think, this all does not much matter; anyway, the eclectic concept of monophyly is really simple.

>******But this is NOT the end of decisions.******
>He has now to decide when he will look at the tree "upwards" versus 
>"downwards".
>Here he decides to look at the tree "upwards" at the 10-changes gap, but 
>downwards at the 5-changes gap
>---------End of decisions.---------

Perhaps I do not understand you well in the matter of upward and downward directions. The eclectic procedure is (in the principle) very simple: having a cladogram we will first find (in this simplistic example!) 10-character gaps -> split the cladogram/set of terminal taxa into between-gap (connected) pieces -> name them (e.g. as families). Then repeat the procedure with 5-character gaps and name them as genera etc.

P Deleporte:
>Consequently, he names clades A+B (supported by 5 changes), A+B+C+D 
>(supported by 10 changes), and grade C+D (supported by 5 changes at the 
>"upper bound"? Or supported by its insertion between the 10- an 5-changes 
>gaps??).

See above. Note also that cladists (well, those who do not like to name all clades) use quite similar procedure: find e.g. 10-character gaps -> do a split here -> name all descendants/terminal taxa as a taxon, etc. Note that the difference in method is already included in the definition of monophyly.

P Deleporte:
>It simply seems obvious to me that supplementary decisions are involved in 
>the eclectic approach, ...
>The supplementary decision concerns when to stop applying one criterion in 
>favor of the other, which is clearly not a concern for the cladistic system.

I hope to show clearly that there is hardly a large methodologic difference. See above how the cladistic and eclectic concepts rely on very similar principles: 
monophyly (of a different kind) + "gaps"

P Deleporte:
>Now the good question seems to be: does it matter at all and why? What is 
>gained, what is lost, and are there more coherent alternative solutions for 
>conveying complex information (markers...)? And the answer should be linked 

Good question. IMO, the cladistic and eclectic classifications simply have different goals: in cladistic concept we want to summarize apomorphies ("evolutionary novelties" in some sense) while in the eclectic one we want to summarize all homologies (i.e. those characters that can be considered "the same thing" within a taxon). Both views have their rationale, use and advantages I believe and there is no reason to view them as mutually exclusive.
Best!
Zdenek Skala