Posted by:
chrish
at Tue Sep 20 22:00:05 2005 [ Email Message ] [ Show All Posts by chrish ]
Is Intergradation really what is taking place here? Is this an example of two subspecies with expanding ranges that are coming together and providing gene flow?
You have to remember that our taxonomy is a snapshot in time based on what we see today and what we can infer about the past relationships from the patterns of variation we see today. You can't predict the future nor base your taxonomy on such prognostications.
So what we see today is two "recognizable" morphs of common kingsnake. One appears to be centered along the gulf coast (not necessarily of TX) and another that appears to be a Chihuahuan desert animal.
What led to their isolation? I don't know. But it appears that in relative isolation they have diverged into two pattern morphs and that this isolation has been lost and now they are interbreeding and there is gene flow between the two formerly isolated populations.
So yes, I think this is an example of two subspecies coming together and losing their identities in the zone where there is gene flow.
Of course, absolute isolation isn't altogether necessary for these types of things, just restricted gene flow for a period of time.
Or is this an example of a wide ranging species that exhibits geographic variation and is in the process of speciation?
I don't know that I can envision how these patterns would evolve in the presence of the current amount of gene flow that would appear to exist between the taxa.
Sure I could envision genetic drift in the somewhat sparse, low density Chihuahuan desert kingsnakes where there is reduced gene flow from the east and west, but I don't know that there is any more data to support that model than the "standard" isolation model. And I'm not sure it is saying anything different anyway.
The only reason I ask is because even though I (we) use the term intergrade, and generally accept it, it really has a very specific meaning, at least IMO, that can not accurately convey what is taking place with every population because of the multitude of different factors at play with various populations.
Agreed. But when I use the term, I am simply inferring that there is gene flow between two recognizable morphs of the population that I believe warrant taxonomic recognition. But of course, there are no "pure" specimens of ANY subspecies. That gives some people trouble. I sleep at night anyway  !
If you can put up a good argument that the two populations are diverging rather than coming back together doesn't really matter to me. At this moment in time, there is gene flow between two recognizeable populations and that is intergradation for me.
Or maybe I'm just making too much of the term "intergrade" and it "only" implies that the population exhibits traits from two generally recognized subspecies, and has no implications regarding mode of speciation?
You can't look into your evolutionary crystal ball (unless you have one - if you do, I'd like to borrow it!) to try and foresee where they are going to decide if the term fits or not. Your taxonomy and its associated terminology only apply to this moment in time.
And you have to have a terminology that isn't teleological. I see lots of discussions of these patterns where divergence and subsequent speciation is proposed as some sort of goal. There is no goal, no endpoint.
As for Texas, I think any splendida east of the Pecos is an intergrade. Why? Because I like those El Paso/Hudspeth county animals and anything that doens't look like them must be made to feel inferior - LOL.
And BTW - having found a lot of splendida in EP and Hudspeth counties, many of them do not have solid black bellies. In fact, the best "sock-headed, perfect pattern" splendida generally don't.
I've hatched clutches from the Hueco Mts and from the Ft. Hancock area that included black bellied and checkered bellied babies.
On a different note - in south Texas you have to factor in the effect of the other big Lampropeltis as well. Blaney (1977) points out that where you find getula, the milksnakes are small. Where you get big milksnakes, there aren't any getula. Maybe that competition is influencing their distribution (although not their appearance)in SoTex as much as anything else?
-----
Chris Harrison
San Antonio, TX
[ Hide Replies ]
|
RE: does the term intergrade have a specific implication? - chrish, Tue Sep 20 22:00:05 2005
