[CPN] Elimination of Art. 10.9 (in Cellinese et al. species proposal)

[Cantino, Philip]

Dear CPN Members,
My concerns about the Cellinese et al. species proposal are mostly practical rather than theoretical.  Although I agree that “the PhyloCode is about naming clades”, I recognize that most systematic biologists are also interested in naming species or at least use species names.  The authors of this proposal consider species to be merely a rank, but many biologists view them as a distinct kind of evolutionary entity.  Furthermore, species names are very widely used by non-scientists, probably moreso than any other taxonomic names.  They are integral to communication in many fields including agriculture, horticulture, forestry, pharmacy, and even certain areas of law (e.g., endangered species protection, import regulations).  In order for the PhyloCode to be accepted by more than just a small subgroup of phylogenetic systematists, it is essential that it not interfere with clear communication about species.  Furthermore, it ideally should provide a means for people to integrate species names with PhyloCode-governed clade names.  If such a mechanism is not provided, it will discourage many people (biologists and non-scientists alike) who deal heavily with species from adopting phylogenetic nomenclature for clades.  Providing such a mechanism is the function of Article 21, which Cellinese et al. propose to eliminate entirely.
The aspect of the proposal to which I object most strenuously is the elimination of Art. 10.9, because doing so would open the door for some PhyloCode users to name clades in a way that will cause confusion for users of species names (I will explain below).  Permitting this would be a disservice to the systematic biology community and the broader society that uses scientific names.
A good example illustrating why it is critical to retain Art. 10.9 can be found in a 2006 paper by Kirsten Fisher (Syst. Bot. 31: 13-30), who was a graduate student of Brent Mishler’s (Brent is one of the authors of the species proposal).  In this paper, Fisher named five terminal clades (each corresponding in morphology to a previously named species) within a subgroup of the moss genus Syrrhopodon by converting specific epithets.  She used node-based definitions with two to four internal specifiers, each of which is a herbarium specimen.  In each definition, one of the specifiers is the type specimen.  The other specifiers are sometimes vouchers from her molecular and morphological analyses and sometimes specimens that she felt represented the geographical breadth of the taxon.  Her trees showed little to no resolution within each of the five terminal clades.   Now, suppose that a future analysis with more rapidly evolving molecular markers and representation of a broader set of populations were to find that a specimen X that Fisher did not use as a specifier is basal to all of the internal specifiers that she did use but identical in morphology to them.  For example, specimen X might key out to borneensis in her key but lie outside the clade borneensis as she defined it.  Of course one could then coin a new clade name (let’s call it papuensis) that would include borneensis plus specimen X, but the name papuensis would correspond in content and morphology to the species that is called Syrrhopodon borneensis under rank-based nomenclature, and the clade borneensis would be a morphologically indistinguishable subset of the species S. borneensis.  This would be a decidedly undesirable outcome from the standpoint of clear communication.  And suppose a later analysis finds a population of S. borneensis that is even more basal than specimen X and yet another name must be coined for the same morphological taxon (but a slightly more inclusive clade)...
Of course analogous problems can occur when converting the names of larger clades, but this situation is less likely to occur because we generally know more about the basal topology of more inclusive clades (at least those that we choose to name) than we do about the topology of populations forming a species or terminal clade.  There may be thousands of populations that could conceivably be basal within a monophyletic species (terminal clade), as compared to generally far fewer candidates for the two basal subclades of a larger clade.  So the likelihood of discovering subsequently that a name applies to a smaller clade than intended is greater for terminal clades.  Furthermore, the impact on the outside world is greater when species names are involved.  A lot of people out there who are not taxonomists, let alone phylogeneticists, care about the meaning of species names, and they don’t like names changing unnecessarily.  It is at our peril that we mess with species names; doing so will be a lightning rod for criticism of phylogenetic nomenclature as a whole.  The authors of this proposal imply (end of their second paragraph) that their proposal will make the PhyloCode “available to all systematists regardless of their views on the nature of species”.  On the contrary, I think that if we were to adopt their proposal, the code would be far less suitable than it is now for people who use species names—which is the vast majority of systematists.
I have concerns about other aspects of their proposal too, but I’ll cover them in a later message.
Phil


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