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Posted by KSF on July 11, 1999 at 11:23:27:
In Reply to: Re: Kisatchie Corns : the debate rages on posted by Don on July 07, 1999 at 12:35:53:
I think the term "intergrade" is confusing. It is meant to describe a group of animals located between the ranges of two designated subspecies at the point(s) where the subspecies' ranges contact one another. To understand what an intergrade really is, you have to take into account the process of gene flow. Gene flow is the transference of genes between individuals in a population, or on a larger scale, between populations / subspecies. This transference of genes is carried out through mating and offspring dispersal. It is not unlike, in principle, the passing of a baton between teammates in a relay race, with the baton representing a particular gene or group of genes. A baton (gene) can get from the 1st runner to the last without these two runners coming into contact because there is a 2nd, 3rd, 4th, 5th, runner and so on. In this way a gene can get from a speckled king in Missouri to a desert king in west Texas (and vice versa) without these two subspecies ever mating. The intergrades are the "baton carriers" in the middle.
Of course, if this gene flow was unlimited speckled and deserts would be very similar. There are limitations to gene flow along the way. This is where natural selection comes into play. Say there is a metal grate on the track and one of the relay racers has feet small enough to fall through the holes in the grate. His particular baton will not make it to the runner at the end, but the other batons carried by big-footed runners will make it past the grate. This is a very oversimplified example, but the general idea is the same concerning gene flow through populations. In nature, the "grates" are various characteristics of the environment which act as barriers to dispersal. A complicating fact is that natural selection acts not on a single gene, but rather on an individal organism (essentially a combination of genes). That is one of the reasons why the example of the runners and grates is very oversimplified.
I like to think of naturally occurring intergrades (or NCIs for short) as animals located in an area containing a higher concentration of "grates". They have genetic similarity to both neighboring subspecies, but something about their environment prevents complete genotypic commonality with either of these subspecies. They are animals with an "environmentally filtered" genotype, if you will. I find these NCIs very interesting for these reasons. You can see why NCIs are very different from a man-made hybrid. KJ has mentioned several times that he also finds such animals interesting, and I suspect for some of the same reasons I mentioned here. I don't think that intergrades represent an incipient subspecies (if such a thing can even exist). There are numerous theories about the mechanisms of speciation, with "experts" supporting each of them. I'm not sure if anyone will ever know he real situation. Like John Cherry said, it is pretty much an unanswerable question.
Concerning the Kisatchie corns, I think they represent an old population of intergrades that no longer has gene flow with the eastern corns. There are disjunct populations of corn snakes in Kentucky, Virginia, Maryland, NJ, etc. The Kisatchies are probably remnants of intergrades that once had gene flow with a now nonexistent population of eastern corns.
KSF
