Rick:
I am reluctant to speculate about how various studies will pan out with respect to mexicana kingsnake relationships, in part because I am involved with one such project. But I can at least try to frame the discussion. Studies such as those by Bryson et al. (2005, 2007—see the SierraHerps.com website for links to those papers) and stuff that is in progress generally seek to reveal the “one true history” of the group. When researchers analyze characters—whether gene sequences or morphological traits—they develop an “estimate” of the group’s history; this is not arbitrary or capricious, but is based on evidence using accepted analytical procedures. Different kinds of evidence can yield “estimates” that might not always agree with one another. For example, if we relied on color pattern characters to estimate phylogeny in modern coralsnakes, we would develop a picture of the group’s evolution that is very different from one arrived at from an analysis of gene sequence data. Of course, we now know that for many groups of snakes, color and pattern are not especially reliable indicators of relationship.
With respect to mexicana kingsnakes, there are several lines of inquiry:
1. How many species are there? (And, despite some differences among evolutionary biologists about the definition of “species,” the vast majority of species of herps would be recognized as distinct species no matter which definition was being used.)
2. Related to #1, what to do about subspecies? The use of “subspecies” in modern herpetological taxonomy has declined as our understanding of speciation and population genetics has increased. As more and more groups of herps are examined in greater detail (more specimens available, examined using more sophisticated techniques…e.g., gene sequences), it has become apparent that things formerly regarded as subspecies of wide-ranging groups are in fact better categorized as distinct species. This topic is much more involved (and interesting) than these few words can convey, but you get the idea. Examples include the tiger salamander complex or the gopher snake/bullsnake complex.
3. In addition to knowing how many species comprise this group, who is related to whom? This is where branching diagrams come into play to represent relationships among various species. We want to know which species last shared a common ancestor. Central to this issue is the relationships between various mexicana-type snakes and nearby triangulum-complex snakes. Talk about a can of worms!
4. Are there independent lines of evidence to support the preferred phylogeny? For example, there may be geological, paleontological, or climatic data that support or refute particular evolutionary scenarios.
5. Lastly, evolutionary biologists seek to understand the processes by which populations (or lineages) of these snakes have become genetically distinctive. Which historical forces were at play in generating the particular patterns of diversification we see? In mexicana kings, while much of the group’s structure could be explained by vicariance (= range fragmentation), there might be places where formerly separated groups have reconnected and now freely exchange genes.
As of this moment, we have a phylogeny (Bryson et al. 2007) that is based on mitochondrial gene sequences. What is needed is an independent estimate based on nuclear genes. And of course obtaining specimens from critical “in-between” areas could be really helpful in this regard. Such areas are noted on the range map on my website…you can see the areas from which no specimens are known. So, in closing, I’d just reiterate my reluctance to speculate on how the last chapter of the book will read, but will instead wait for the evidence to be uncovered…and then we’ll just follow the trail of wherever it leads!
Cheers,
Bob
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