After spending some time on sierraherps (which alternately could just be called Bob’s Amazing Mexicana Site) I decided to dust off some grey matter and invest a bit of time reading the new papers supporting species level classification of the different forms of mexicana.
The short term report is that at this point I still don’t get it! There is enough incongruence to cause me to question the method or discount the conclusions because the sample pools were simply statistically insignificant. Nothing I’ve read so far appears note worthy enough to discount the obvious geographic and morphological relationships between thayeri, mexicana and greeri. I know the argument is made that geographically these populations are currently disjunct but it’s highly plausible that at the peak of the last ice age this was not the case.
A lot of these conclusions also rely on the accepted assumption that mtDNA mutates at a predictable rate but IMHO this is a leap of major proportions. One could alternatively hypothesize that background mutation rates are much more frequent and that mutations are simply not routinely manifest in the general population because the ecosystem is stable and 1) the mutation confers no advantage in the existing matrix and or 2) the mutation confers a disadvantage relative to the general genotype which is specifically adapted to existing conditions. During times of rapid ecological change however this equation would be turned on its head. For instance, as the last ice age faded, even gradual changes to hydrologic weather conditions and vegetative patterns stressed population such that some even became extinct. If one of these happened to be a cornerstone species a more rapid change or perhaps even collapse of a local ecological system might result. During such a time the presences of numerous background mutations would increases the odds that some individuals would have the capacity to exploit the new matrix and initiate new populations in newly created niches. Given this scenario shifts in mtDNA that appear in populations might be less a function of time between significant mutations and more a factor of time between major environmental change.
In this above scenario of rapid ecological change it is also likely that barriers to reproduction that existed between populations in stable conditions would vanish. The resulting gene flow would facilitate the creation of more varied genotypes again increasing the odds that specific individuals would have the capacity to adapt.
Given this view I did not find it surprising that as the climate warmed the more mountainous forms (mexicana and greeri) increasingly diverged from the more lowland form (thayeri). I also did not I find it surprising that some level of integration with triangulum occurred and that the resultant dispersal of DNA would show a relationship between thayeri and milksnakes of the continental US and that central American milksnakes would show a closer relationship with mexicana and greeri. Geography alone make this rather obvious.
What I don’t get that this information seems to indicate that all tri-color kings are more closely associated than we might have assumed but we’ve concluded that despite this thayeri, mexicana and greeri, the three forms at the very hub of the last cycle of adaptive radiation deserve species level status. Like I said I don't get it.

















