Not Up, But Down


While I may wail on Linnaean Systematics and the issues with ranks, and the use and potential loss of the concept of the “genus” as an entity separate from that of the species, some authors out there are going at it in the opposite direction. That is, rather than concerning themselves with the issue of supraspecific ranks, they are looking as subspecific ranks. Subspecies, in fact.

Enter Oliver Hawlitschek and Frank Glaw (Zoologische Staatssammlung München, München, Germany), and Zoltán Nagy (Royal Belgian Institute of Natural Sciences, Brussels, Belgium), who just published a new paper revising the phylogeography and phylogeny of Comoran spotted tree snakes (Lycodryas sp.).The snakes of the Comoros, north of Madagascar, are almost exclusively restricted to two groups, Lycodryas and Liophidium mayottensis (Peters’ bright snake). Evaluation of museum specimens with collection data indicates to the authors that, rather than one species, there are four separate groups of Lycodryas. These snakes clearly differentiate on mitochondrial and nuclear DNA lines, and supplementary morphological analysis indicates that there are two groups, with two subgroups; moreover, each subgroup was restricted to its own island (of the four major Comoran islands). Confused with this is that these snakes had otherwise also carried the names Lycodryas maculatus and Lycodryas sanctijohannis. This, as it turns out, is not an issue, as it appears that these represent the same taxon … in general. Hawlitschek and his coworkers found that they could do several things:

1. Refer all taxa to one species, and erect new subspecies names for each of their new groups.
2. Refer all taxa to new species, and erect new species names for each.
3. Do nothing.
4. Or, do a mixture of 1 and 2.

Explicitly, the authors chose an even-handed approach: They determined that, while genetic variation supported “species” status for each — that is, there was a phylogenetic distinction among the snakes (under Cracraft’s 1983 formulation), there was distinct morphological support for only the two broader groups. Still, this was more refined than currently considered. The authors chose to recognize the second group of Lycodryas snakes as a new species, called Lycodryas cococola (which, crazy as that sounds, does not honor the soda manufacturer, but is Latin: Cocos, for the coconut palm, and –cola, for “inhabiting”, thus “dwelling among the coconuts” — or something). The first group, though required sinking of the otherwise popularly-used sanctijohannis into maculatus, which was resurrected from obscurity, and further recognizing as a subspecies another “sunk” subspecies, comorensis.

The authors seem justly wary of the Linnaean System, recognizing that it has few harbors among vertebrate zoology (despite the number of times I see its conventions used), but here they adhere to the ICZN, which mandates the subspecies, like “family-rank” taxa, abide by the principle of coordination: the type species which contains subspecies also grants the name to its type subspecies: thus, Lycodryas maculatus‘s type subspecies is Lycodryas maculatus maculatus. The same is true for Lycodryas cococola cococola, leaving only the second subspecies innocens (named for the paranoia of the locals who fear these non-venomous, non-deadly [to humans] snakes and which leads them to kill them, even above other snakes of the Comoros).

The phylogeography is cool, too:

The next most interesting thing about this paper though, and this really should be a primer for others, is that much of the groundwork for the dispensation of these snakes comes in the introduction. The abstract is none too shabby, but the introduction shows that the authors really do seem to give more than one flick of a tongue at the issue of what to do.

Their introduction is worth reading, in full, and I wish I could pull out nice pieces, but the heavy use of citations (81 different papers referred to by the end of the introduction, alone!) makes the transcription tedious, so just go here and plow right in.

Cracraft, J. 1983. Species concepts and speciation analysis. Current Ornithology 1:159–187.
Hawlitschek, O., Nagy, Z. T., Glaw, F. 2012. Island evolution and systematic revision of Comoran snakes: Why and when subspecies still make sense. PLoS One 7(8):e42970.

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