viernes, abril 18, 2008

Vouchers, types and specimens

Prompted by the closure of Utrech Herbarium, Chris Taylor write two interesting posts about the nature of type specimens and vouchers (of molecular studies). In both cases Chris remarks about the importance of a comparison specimen to resolve some taxonomical problems.

In a more implicit way, the post about vouchers remarks how molecular tools can be very important, but in a some way or another, to made a proper 'molecular taxonomy' you need to rely on a proper morphological (classic) taxonomy.

I a post that I made some time ago, Chris point me some of that remarks, and actually I think that my disgust with type specimens is not the types, but the bad practice around it, specifically, that many specialist from old days (and maybe some actual ones), propose hundreds of new species based on telegraphic descriptions.

The other thing about type specimens that I do not like, is that it seems that there is an 'single specimen taxonomy', I thing that every specimen in a collection is equally valuable. For me, most important than the type speciemen information is the 'examined specimens' list, that usually include individuals of different sexes, and ontogenetic states.

But I think that new generation of taxonomists are moved into the right direction. First there are new approaches intended to store and provide access to information on an specimen basis, I specially like [1], even if the data are not made public (I prefer public data, but I understand that a taxonomist want to keep his/her data with him after a long work of several years, for at least the same amount of time!), it allows a quick reexamination of material.

The second point, but sadly it is not very popular in third world countries (and even in first world ones), is that every, I repeat every taxonomic contribution would be made under a rigurous phylogenetic framework. That is, character discussion, published data matrix, and phylogenetic tree-based classification.

Character discussions allows a more objective definition of the examined characters, as inside-study coherent terminology, because phylogenetic characters would be the same character across several species.

Data matrix, shows in a easy readable form (specially if you have a phylogenetic data editor, there are several free on the net) several characters examined for a particular terminal (that is a set of examined specimens), which shrink the usually lengthly (and bored to read) description section of the paper. That part can be reserved to particular characters that are not used under the cladistic analysis (for example, colors, measurements, proportions), or particular character scorings (explaining some particular scoring), biological information (such distribution, ecological aspects), links to figures/pictures (electronic or in print) and the list examined specimens. When a character is scored, the author of the matrix is saying that he/she view that character in the species, it also includes a list of non-seen characters (usually typed as '?'). Note that the matrix is an excellent way to fuse the information stored with the several specimens examined, so linking data from the specimens and from the matrix is direct [1].

Finally a cladogram-based classification, allows to maintain the information from the analysis, tightly binded with the taxonomy. If someone proposes a new genus, it will show that the difference with other ones is a really different group, and not a highly appomorphic group inside a previous established genus. A classification need evidence that support each proposed taxon, and the cladogram is the well know form to found evidence of grouping.

[1] Ramírez, M. J. et al. 2007. Linking of digital images to phylogenetic data matrices using a morphological ontology. Systematic Biology 56: 283-294. doi: 10.1080/10635150701313848

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