Hi Wulf,


>>Consensus would acutally still accept propsals based on e.g. the BSC, wouldn't they?

Consensus is what develops over time after a proposal is first made in the literature - an increasing proportionof workers will either use or disregard the new arrangement. Also, where you look will make a difference. If a new taxonomic proposal is well supported, then academic publications will usually accept it quickly, whereas it takes a bit longer to percolate into the herpetocultural literature and when it comes to the taxonomic literature - consensus becomes synonymous with intertia. The average toxinological journal comes straight out of the 1960s when it comes to the taxonomy used.

>>Evidence seems to be the most convincing thing in taxonomy. But evidence also is a matter of knowledge and the objective view of the results and argumentation presented in a paper.

Evidence is primarily data, and second their analysis and interpretation.

>>
>>Which methods should be used to be evident?

That or those best suited to answering the question you are asking.

This requires in particular an awareness of the strengts, weaknesses and limitations of the different methods and markers.

>> Some workers prefer morphological characters, others say that DNA analysis would be the most objective thing and therefore the most evident.

Depends on your organisms and what question you are asking. If, for instance, you want to test whether two differentiated "forms" occur sympatrically where they meet, or whether there is an intergrade zone, a morphological analysis may be entirely adequate and much better than mtDNA.

On the other hand, it is certainly true that very often, the best bet is to use different markers in combination - molecular morphological markers together can be reciprocally illuminating and their combination may be much more powerful than the sum of the parts.

>> But which one to use? mtDNA or nuclear DNA?

Depends on what you are trying to do. Also, what nuclear DNA marker? A gene sequence? Microsats? AFLP? These all tell you different things, make different assumptions, and have different logistic requirements.

A phylogenetic analysis at higher taxonomic levels is best done using both mtDNA and nuclear gene sequences. On the other hand, if you are trying to determine species limits, then a combo of morphology mtDNA, or even microsats or AFLP (if you can get the required sample sizes together) would be much more appropriate.

> Can every base pair really be used as a character?

Depends on context. If you are running a phylogeny on one single gene or a single non-recombining set of genes, then yes. On the other hand, if you have 20 morphological characters and 1000 variable base pairs, then that would be a different question.

> Is it a consensus today, not to use the BSC anymore because the reproductive isolation can not be tested in the wild?

First, let's distinguish between species concept ("what is a species" and species diagnosis criteria ("how do we diagnose it?".

Under just about any evolutionary paradigm, a species is basically a separate evolutionary lineage. Most of the so-called "species concepts" such as the BSC are in reality centered around diagnostic criteria - the BSC simply states that reproductive compatibility is the criterion for recognising species. I think pretty much everyone would agree that reproductive isolation DOES indicate separate species status, since two lineages that cannot exchange genes are clearly evolving separately. However, lack of reproductive isolation is no loger viewed as precluding separate species status by most practicing systematists nowadays, partly because of the impossibility of relevant testing for allopatric taxa.

Cheers,

Wolfgang
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