It's been two years in the making, but the ICZN decision on Drosophila has finally been announced (ICZN, 2010). You may recall that an application had been submitted (Linde et al., 2008) to make Drosophila melanogaster, the subject of countless genetic studies, the type species of the genus instead of the current holder of that title, D. funebris. See previous posts here and here for background details.
And the verdict: by a surprisingly large margin (23 to 4, with one absence), the Commission has turned the proposal down. Drosophila funebris remains the valid type species of the genus; D. melanogaster retains the potential for reclassification. Those of you with a particular interest in the workings of nomenclature* would do well to get hold of a copy of the decision. In light of the higher than usual public interest in this case, the unusual step has been taken of publishing individual comments from each of the commissioners on the reasoning behind their decisions. As well as the insight provided into this particular case (and it's worth noting that some of the commissioners on both sides of the floor ended up voting against their own initial sympathies), some of the comments provide interesting talking points about the role of nomenclature in general.
*Yes, we do exist. I'm afraid the doctors say that there's nothing they can do.
Some of the reasons given for voting against the proposal were reasonable, others less so. A. small number of commissioners voiced the complaint that the proposal was asking the ICZN to endorse a particular taxonomic method; as I argued in one of the previous posts, it did no such thing and I am rather disappointed that this issue was raised. Some commissioners also turned down the proposal on the grounds that it was premature (Miguel Alonso-Zarazaga stated that he "felt that the authors of the case had not allowed the community to have a healthy discussion of their proposals, since the ‘detailed phylogenetic studies’ mentioned in the case were still largely unpublished, and were thus hypothetical"). However, while the proposal may have been precipitated by an as-yet unpublished study, the results of that study are hardly novel. As pointed out by László Papp in his comments on his supporting vote, the issue that any subdivision of Drosophila would require the removal from that genus of D. melanogaster has been under discussion for at least 35 years (a time when, I should note, purely phylogenetic considerations were often considered less significant).
Less trivial are the concerns that the proposal introduced a higher overall nomenclatural instability than the current status quo and that it may have set an uncomfortable precedent. The commission was being asked to choose between maintaining Drosophila for a smaller number (about 300) of species including some very well-known taxa, or a potentially much larger number (up to about 1100) of mostly less familiar species. Should "celebrity names" carry that much greater weight? Also, while the combination Sophophora melanogaster may be unfamiliar, there is no actual ambiguity about to what it refers.
Some commissioners, as well as many of the ICZN's press statements, raised the argument that "drosophila" could still be used as an informal name for Sophophora melanogaster. True, as far as it goes, and not unprecedented: names such as "azalea" and "cosmos" continue to be used despite the genera of those names being stricken from the technical literature long ago. Nevertheless, this is not anywhere near a satisfactory solution. As a corollary example, a number of recent authors have proposed restricting "Aves" to the crown group of birds on not unreasonable grounds. The supposed divide between technical and vernacular names has done nothing to dissuade people from objecting to the idea that creatures such as Archaeopteryx and Ichthyornis may no longer be "birds".
My thanks go to Kim van der Linde (first author of the proposal) and Elinor Michel (secretary of the ICZN) for sending me copies of the decision. Kim's own reaction to the ruling can be read here.
REFERENCES
Linde, K. van der, G. Bächli, M. J. Toda, W.-X. Zhang, Y.-G. Hu & G. S. Spicer. 2007. Case 3407: Drosophila Fallén, 1832 (Insecta, Diptera): proposed conservation of usage. Bulletin of Zoological Nomenclature 64 (4).
D'oh, you beat me to this by an hour, and with a better title and insider insight...
ReplyDeleteI'm going to sulk back to my dark room and shoot light beams through mantis shrimp eyes until I feel better
Christopher, you missed the same obvious point as the commissioners:
ReplyDeleteThe genus is going to be split in four major clades. The name of the species in two clades, together 628 species, will change regardless. of the two remaining clades, the clade with funebris contains 304 species, the Sophophora subgenus contains 332 species (species counts as in original application). So, now that funebris remains the type species, the name of 28 more species are going to be changed. More over, this decision results in renaming of ALL species for which the genome is sequenced (14 species in total), instead of 3.
Having your cake and eating it too?
ReplyDeleteIs there a reason to raise the subgenera to genera? If there isn't a compelling reason, then I'd be inclined to ignore any generic name changes for melanogaster. Ranks are arbitrary by nature. A primary function of a taxonomy is to provide stability and retaining subgenera would seem to both maintain stability and provide sufficient phylogenetic context. If a few smaller genera are already running free, that complicates matters, but doesn't seem an insurmountable difficulty.
Full disclosure - I have pushed to raise subgenera to genera for mites used in biological control, but the trashcan genus was already paraphyletic and even the species were misattributed there, so the whole mess needed cleaning up and not too many people get upset about a predatory mite name change.
Also, when I taught Medical & Veterinary Entomology I used Aedes (Stegomyia), Aedes (Ochlerotatus), etc. Stegomyia does carry useful life history and epidemiological information, but it is a terrible search term. I thought the revolt of the journals a useful point in teaching - but not for the importance of systematics!
No cake for Drosophila
ReplyDeleteI made my comment above before reading the history and opinions at the ICZN webpage. Pretty fascinating range of opinions - not the least of which is that most would seem to see 'stability' for the rules as more important than stability for the name. I'm not sure that I agree with any of the arguments completely, but I found Pringent's points well argued.
Recently published and in press molecular phylogenies support a diphyletic Acari (something I have long believed on morphological grounds). One colleague has already suggested recognising only one lineage as mites. So, the other 13,000 described species would be called something else? I guess I will have to review my opinions on nomenclature and phylogeny and see if they make any sense.
The reasons for raising the subgenera are pretty compelling, particularly for Sophophora. If you look at the tree that Michael reproduced from Kim's supertree paper, it appears that even describing Drosophila in its current sense as paraphyletic is misleading - it's significantly polyphyletic with at least three widely separated clusters even if one was willing to accept a certain amount of paraphyly. As I said in a comment on Kim's post, I feel that the only feasible approach now is to force the issue by splitting the genus - once again, an action that is now overdue by some 35 years!
ReplyDeleteSigh. It all just adds to my growing conviction that the binomial system itself is fundamentally flawed.
As regards mites, I would have thought monophyly of Acaromorpha (Acari + Ricinulei), whether "Acari" themselves are monophyletic or paraphyletic to Ricinulei, was pretty much a certainty. No other arachnids share their unique development with six-legged larvae.
I have a feeling that people (geneticists anyway) will be calling it Drosophila regardless of what the ICZN does.
ReplyDeleteSo I think this was a bad decision since it creates a division between what taxonomists call it and what people who work with it call it.
But maybe, for this very reason, the genus won't be split.
Christopher wrote:
ReplyDeleteSigh. It all just adds to my growing conviction that the binomial system itself is fundamentally flawed.
David Marjanović has described binomina as a "curse". I'm entirely inclined to agree.
I have added a more extensive phylogeny to the http://www.kimvdlinde.com/professional/DrosophilaSplit.html page. Have fun
ReplyDeleteMite Monophyly Not
ReplyDeleteActually, a distrust of mite monophyly goes back a long way, but it took me a while to understand why.
Although the hexapod larva and gnathosoma were considered strong linking characters, that was before it was noticed that ricinuleids have them. To me, the Shultz Acaromorpha solution was never very convincing. I've only studied one species, Pseudocellus pearsei, but relating that 'hooded tickspider' (as Fahrein et al call them in their BMC Genomics paper) to Acariformes is beyond my abilities (maybe a bit to Parasitiformes). In any case, I suspect that the hexapod larva is an ancient chelicerate developmental stage retained in three current terrestrial 'arachnid' orders. Think of how xiphosurans develop - and remember that Acariformes and Opilioacarida also have a hexapod prelarva.
Also consider that two or three basic adaptations to life on land are inherently different between basal acariform and parasitiform 'mites': respiration (cuticular vs tracheate), the formation of the subcapitulum (deutosternum+tritosternum [mentum]) vs deutosternum), and sensory setae (trichobothria, solenidia with rows of pores vs no trichobothria, tip pore chemosensory setae) - the difference in chemosensory setae is questionable, they really aren’t well studied. There are lots of other basic differences in bauplan: being a ‘mite’ may be a grade of evolution.
I think you need to go back into the Silurian oceans to find any common ancestor of ‘mites'. Once there, anything goes.
Dabert et al. have a paper in press in Molecular Phylogeny and Evolution that is worth a look. The recent Regier et al. in Nature (which does not support Acaromorpha) has only a few mites, but at least a couple from each lineage. I’ve seen other papers in review with similar findings, so looks like the molecules are against mite monophyly.