This is a taxonomic proposal. Whether it is accepted or not will depend on whether the author who proposed it has a convincing argument. From what I hear, Burbrink's (2002) proposal to split the cornsnake into 3 species has not been well received by other systematists. His study, however, is very informative. It shows that emoryi is the oldest subspecies and that the other subspecies appear to have migrated to the east from the area now occupied by emoryi. That means the red coloration seen in E. g. guttata most probably evolved from a largely gray/brown colored animal like E. g. emoryi.

Quite obviously from this tree, the corn snakes share a single common ancestor. Burbrink is splitting the corn snakes NOT because they form a polyphyletic group, but he is splitting E. guttata because he is applying the so-called 'evolutionary species concept.' Burbrink writes: "The three lineages of E. guttata are each geographically confined to discrete areas, generally exclusive of one another, and most likely represent three distinct species"

Ernst Mayr (This is Biology) criticized this concept thusly:

'The evolutionary species concept has been promoted particularly by paleontologists who follow species through the time dimension. According to Simpson's (1961:153) definition, "An evolutionary species is a lineage (an ancestral-descendant lineage of populations) evolving separately from others and with its own unitary evolutionary role and tendencies." The main problem with this definition is that it applies equally to almost any isolated population. Also, a lineage is not a population. Furthermore, it side-steps the crucial question of what a "unitary role" is and why phyletic lines do not interbreed with one another. Finally, it actually fails in its objective, the delimitation of species taxa in the time dimension, because in a single gradually evolving phyletic lineage the evolutionary species concept does not permit one to determine at what point a new species begins and where it ends and which part of such a lineage has a "unitary role." The evolutionary species definition ignores the core of the species problem: the causation and maintenance of discontinuities among contemporary living species. It is rather an endeavor to demarcate taxa of fossil species, but it fails even in that endeavor.'

Indeed, Burbrink points out that there are some isolated populations '(i.e., specimens from Kentucky in the eastern partition and Colorado specimens in the western partition) are separated from the large continuous partitions and may represent independent evolutionary lineages, they will not be considered species here because they have not been appreciably examined morphologically or molecularly.'

Just as Mayr pointed out, any isolated population can be considered a lineage under the evolutionary species concept. But since a population is not a lineage, and since these "lineages" of corn snakes are not reproductively isolated from one another, most biologists who still subscribe to the almost universally accepted biological species concept will probably reject Burbrink's proposal.

[ Reply To This Message ] [ Subscribe to this Thread ] [ Show Entire Thread ]