A new paper by Burbrink and associates (2011) indicates that two distinct genetic lineages exist within the taxon currently known as Lampropeltis pyromelana. Based entirely on evidence obtained from the sequencing of one mitochondrial and two nuclear genes from 45 tissue samples, the authors assert that these lineages have been separated since before the Pleistocene and possibly even longer. Algorithmic extrapolations from their samples also apparently document that there has been little or no genetic exchange between these two major lineages throughout this extended period of separation, even during the Pleistocene glacial periods when the currently inhospitable habitat separating them was somewhat ameliorated.
As a result, the authors, applying the Evolutionary Species Concept (ESC), have contended that each of these two lineages bear adequate genetic divergence to qualify for full species rank. The northern form, on the Colorado Plateau, north of the Mogollon Rim, would retain the L. pyromelana designation since the type locality for that taxon lies north of the Rim. The remaining portion of the "former" L. pyromelana would assume the name "L. knoblochi" as that is the only remaining available name from within its range.
When considered from the Biological Species Concept (BSC), however, where the more pragmatic development of reproductive incompatibility is a requirement for acknowledging that speciation has occurred, one must consider whether geographical and temporal separation, even when accompanied by some degree of genetic divergence, is sufficient evidence of a speciation event.
The question should be: if the hostile desert environment currently separating these two purported species were to become once again inhabitable by both of them, would they behave as totally different species, avoiding reproductive contact with each other, or would the populations successfully interbreed with each other as conspecifics. The virtually identical morphology of populations above and proximally below the Mogollon Rim suggests that the latter scenario is more likely than the former.
An additional problem with the Burbrink et al. proposal lies in its apparent disdain for morphological criteria of any kind. This is evinced by its failure to advance any method of practically (i.e., morphologically) distinguishing between the two proposed taxa where their ranges approach each other along the Mogollon Rim. Presumably field biologists would be reduced to consulting range maps to determine which "species" they were dealing with at any given location.
Further evidence of the authors' "molecular chauvinism" is displayed in their remarkable failure to mention that their proposed "Lampropeltis knoblochi" is either polymorphic or is composed of at least two geographic races: a ringed form virtually indistinguishable from their restricted L. pyromelana in the northern portion of the range, and a blotched form that was the basis for Taylor's (1940) original description of L. knoblochi to the south.
A further taxonomic action taken by the authors of this paper is the sinking of the subspecies infralabialis, originally described by Tanner (1953) on the basis of specimens having one less infralabial and 50% or more of white rings complete across the ventral surface. While we agree with this move, we doubt that the genetic evidence presented by Burbrink et al. actually serves to discount a diagnosis that was morphologically based. However, there appears to be a wealth of anecdotal and regrettably unpublished data indicating that the morphological variation in L. pyromelana (sensu lato) is greater than that described by Tanner (op cit.) in his original diagnosis of infralabialis, and consequently that taxon should no longer be recognized.
Therefore, while accepting the genetic divergence between the two lineages as demonstrated by Burbrink et al., we are not currently convinced that it fully supports their proposal that these groups are sufficiently distinct from each other to warrant full species status. Consequently, until further evidence is obtained by different methodologies, we at SWCHR will conservatively recognize this complex as follows:
Lampropeltis pyromelana (Sonoran Mountain Kingsnake)
Lampropeltis pyromelana pyromelana (Arizona Mountain Kingsnake) - ranging above the Mogollon Rim in Arizona, Nevada, New Mexico, and Utah; consisting of a ringed morph only.
Lampropeltis pyromelana knoblochi (Chihuahuan Mountain Kingsnake) - ranging in the Madrean highlands of southeastern Arizona, southwestern New Mexico, thence southward into Chihuahua and eastern Sonora; consisting of a ringed morph in the north and a blotched morph in the south, with occasional intermediate specimens appearing in southeastern Arizona and adjacent Mexico.
Burbrink, F.T., Yao, H., Ingrasci, M., Bryson, R.W., Jr., Guiher, T.J. and S. Ruane. 2011. Speciation at the Mogollon Rim in the Arizona Mountain Kingsnake (Lampropeltis pyromelana). Mol. Phylogen. Evol. 60: 445-454. [PDF]
Tanner, W.W. 1953. A study of the taxonomy and phylogeny of Lampropetis pyromelana (Cope). Great Basin Nat. 13: 47-66.
Taylor, E.H. 1940. A new Lampropeltis from western Mexico. Copeia 1940: 253-255.
14 OCT 2011
SWCHR Committee on Common and Scientific Names
Tom Lott, Committee Chair
Riley J. Campbell
Gerald Keown (ex officio member)
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