Melanistic populations of black rats, etc, continued (long)

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Posted by Terry Cox on January 14, 2003 at 06:29:30:

In Reply to: I was hoping to ge a repsonse . . .> posted by terryp on January 13, 2003 at 21:33:21:

In the part of the article I quoted included several other species as examples which should be added to the Kentucky Black Rat Snake invasion(lol) of this forum. We can't let them have all the fun. I was hoping to draw some Asian or South American species into it. Diones have a wide range like the black rat snake and they vary in color too. There are light phase diones and dark phase diones, the diones from Tembrosia can be very dark with little of the pattern visible because they get dark. I also think there is definately support for the fact that altitude and temperature have an influence in color darkness. Your South Korean diones can be dark,like the ones I got from you, or a lighter phase, the ones I'm hoping for this spring. Are they from different elevations or areas of that have a significant temp change?

Terry, first just taking this aspect of the South Korean dione, here's some comments. Some of the babies are a little darker, but not melanistic, imo. These are just from one pair from the Seoul, S. K. area. The babies also tend to be darkest from birth and get lighter, as they get older. I believe the ancestral form came from the north and mountainous areas, where it's much colder, and are evolving into a lighter form in the southern parts of the Korean Peninsula. It remains to be seen, but I'd like to see some more specimens from that area of Asia.

What seems to be happening with captive programs is that we breed selectively for the desired traits. My first CB offspring was raised up and bred back to the w/c mother, and that's how I got the clutch last summer with lighter colored babies. If we keep doing this, they'll get lighter and lighter genetically, imho. Some of the babies from the '02 clutch have some pretty nice coloring. Put that with the great personality traits of this variant and it's size, etc, and we're being to have the makings of a fabulous pet snake.

:from you Terry. I think the threads concerning the Kentucky black rat snake warrants discussion taking all the species into account. Those guys in Kentucky are showing on a state scale what should warrant a much broader scale discussion. The discussions on color and pattern are not unique to Kentucky. It seems like it if we don't take advantage of a post and move into the discussion of all snakes. Phil has just mentioned Black Pines, (pituophis lodingi) now he has brought in a snake that is not Elaphe. I read that the Black Pine is considered the only melanistic pituophis. My partner Del and I have a trio that shuld hopefully breed this year that we obtained from John Ginter. They can be quite black with barely any pattern at birth or can be lighter with alot of visible pattern that pretty much disappears as the snake ages. The male and one of the females were very black with very little noticeable pattern and one female was lighter with quite a bit of pattern when we received them as hatchlings from John. The lighter one has gotten darker and the pattern is hardly visible now. I agree that there is gray rat snake influence in some of the populations of black rat snakes in Kentucky. I also think that one or several of those poulations have developed melanistic traits from inbreeding ones that have the mutant gene and survived to breed in the range until you have a melanisitc black rat snake that has gray rat snake influence in them. Maybe I'm going to far with that, but I'm just going with the discussion and what I can research.

Now, from this part of your discussion, I'll continue. Your example of the black pine is interesting. Who knows what all the variables are there that have influenced it, but it seems the melanistic gene has taken over from selective pressure and in this one population and now breeds true for the whole population.

I don't know if there is intergradation with another population, but there could be genes from a normal population floating around in the black pines. At any rate, when they mature from a lighter form to the darker form, ontogeny seems to me to show them evolving from the lighter form to darker, in this case. Also, I don't know what selective pressures there were on the population to influence the evolution of the melanistic population. It could be a combination of isolation, harsher environmental conditions, and habitat type from my opinion, from what little I know of their habitat, etc.

When we look at the black ratsnakes from KY, we are looking at a small portion of that subspecies' range. ASAMOF, according to some taxonomists (Burbrink, etc.), there may be another ratsnake species with influence on KY rats. Most of my experience has been in Ohio and Indiana with the black rats. They tend to get lighter with more pattern as you go west in those states too.

What I find interesting is that there are pockets where the black rats are really black (virtually all black), they can be widely separated, and it's difficult to explain why. I think the melanism is at least partly explained by the harsher conditions farther north and at higher elevations, like you said, and can also be influenced by the type of habitat. In other words, a population living in a forested area will tend to be blacker than a population living in essentially grassland. These pops. could even be isolated from each other, to some degree at least. I have no idea what all the influences are, however, or even where all the more "melanistic" pops. are.

It's an ongoing debate, Ter, and it's interesting to see what happens in our collections with certain species. I like species that have melanistic specimens. ASAMOF, one reason I'm going to start with L. m. thayeri, eventually, is because of it's melanistic form. I like seeing those black ones pop out occasionally. Variety is cool. I suspect that hobbyists will add much to this kind of science in the long run. Good topic.

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