|
21-28 of 28 messages
|
Previous
Page 3 of 3
|
|
RE: Validity of C. horridus atricaudatus
|
Reply
|
|
by CAISSACA on August 21, 2005
|
Mail this to a friend!
|
I always get a giggle out of these threads. Here, in the middle of a thread that started out with a post complaining in effect that Ginger Clark did not recognise a split when she should have done, half the rest are complaining that scientists do far too much splitting to make a name for themselves. It seems that whatever scientists do, they are just a bunch of nitwits who have no idea of the animals. Thank god for august forums of experts such as this, where good old common sense can flourish unhindered by details like data or evidence.
Now, in case anyone is actually interested in the science rather than just in slagging it off, here are some comments on the Clark et al. paper and associated issues.
First, most modern taxonomists do not in fact like to recognise subspecies at all. The concept is generally felt not to be particularly useful in describing patterns observed in animals. If two groups of animals represent separate evolutionary lineages (even if there is some potential for genetic exchange between them), then they should be considered as separate species, if they are just different varieties but part of one evolutionary lineage, then they should not receive taxonomic recognition at all. The Webster's dictionary definition used by Chad Minter would have been the kind of working model used in the 1960s. Biology has moved on from there, with different ways of thinking and new methods - it would be worrying if it hadn't. Also, regarding the third of Chad's criteria (they hybridise) is irrelevant, since all that that demonstrates is that they are not different species - that was never under discussion, so it contributes nothing new to the debate.
Second, let's try to get it into our heads that SAYING THAT TIMBERS AND CANEBRAKES ARE NOT DIFFERENT SUBSPECIES IS NOT THE SAME AS SAYING THAT THEY ARE INDISTINGUISHABLE!!! The fact that you can tell a lowland horridus from a highland horridus is not being denied - the authors of the Clark et al paper also have eyes in their heads, and, in case anyone was unaware of it, at least two of the authors, Savitzky and Brown, are well-known fieldworkers with extensive experience of the species - I dare say they can tell lowland from highland horridus as well.
Now a few specifics.
First, the traditional horridus-atricaudatus split is a north-south split. If these subspecies were to be of any relevance, one would therefore expect a nice north-south split in the genetics as well. Instead, we get an east-west split - i.e., exactly the OPPOSITE of what the cherished two-ssp.-taxonomy would have predicted. Not much support for the timber-canebrake split there.
Then, Chad wrote:
"Clark also makes the statement "Analysis of molecular variance demonstrates that traditional subspecific divisions explain only 3.5% of variation, whereas the alternative geographic classification (southern, northern, and western regions) explains 18.6% of genetic variation."3
This indicates that Crotalus horridus and Crotalus horridus atricaudatus are genetically distinguishable from one another. "
Nope. It means that out of all the genetic variation in Crotalus horridus, only 3.5% (i.e., next to nothing) is accounted for by the two ssp. split. Or, in other words, if you take a random "canebrake" and compare it to both another random "canebrake" and a random "timber", you have almost even odds that your initial canebrake will be more genetically similar to the timber than to the second canebrake. Basically, a southeastern canebrake is much more genetically similar to a northeastern timber than to a southwestern canebrake.
The three-taxa-hypothesis (northeast, southeast, west) is better at explaining the patterns of genetic variation, but that does not mean that it is the best explanation. The basic pattern that is revealed by Clark's data is a two-way east west split, which, as stated above, could not be more at odds witht he conventional horridus-atricaudatus split. Statements such as "She threw the (genetic) feathers on the table, she threw the (genetic) bill on the table, she threw the (genetic) webbed flat feet on the table, she played the (genetic) recordings of "quack quack quack" then just when you're getting to the part in the paper when you expect her to declare "It's a Duck!" .. she twiddles her toes in the sand and murmurs in a squeaky and cracking little voice "uuhmmmm ... it's not a duck"" can only be attributed to remarkably selective reading! The genetic data very clearly do NOT support the traditional timber-canebrake divide. Moreover, although it is entirely true that taxonomists often disagree on many things, I cannot identify any current line of thinking in biology that would make anyone argue that Clark et al's data support the conventional subspecies.
Let's look at another few arguments that are often brought up:
"Timbers den, canebrakes don't, therefore they are different ssp.". Hmmm.... "Eskimos live in igloos, Amazonian Indians live in wooden huts, therefore they are different ssp., right?" Hmmmm - it wouldn't have anything to do with the fact that there is not much ice around in the Amazon whereas wood is a scarce commodity in the high Arctic? Similarly, might the fact that montane horridus den whereas southern coastal plain specimens don't just conceivably have something to with the fact that when temps drop to -30 C in the winter, you'd better find a very deep shelter, but one that will warm up quickly once it gets warmer in spring, whereas that's not so much of a priority in the southeast, where temps don't drop much below freezing? And that it is the relative scarcity of such sites in the mountains that leads a number of specimens to congregate in the same place?
"Canebrakes have neurotoxic venom, timbers don't" - here is the relevant part of the abstract of the paper that highlighted the highly neurotoxic nature of some of these venoms: "The distribution of canebrake toxin was limited to two separate regions, including a region of Louisiana, Arkansas and Oklahoma, and a separate region from southeastern South Carolina through eastern Georgia to northern Florida." In other words, canebrakes from many parts of their range do NOT have neurotoxic venom, so venom is not a simple distinguishing character of the two. The devil is in the detail.
In summary, the likely story is that during ice age cold phases, C. horridus was restricted to the southern part of its present distribution, and most probably consisted primarily of "canebrake"-like snakes. When it spread out again after the climate warmed up, two C. horridus lineages came to occupy the Appalchians, and evolved what we now call the "timber" colour and patterns, presumably as an adpatation to different habitats (snakes inhabiting different vegetational zones often show quite substantial colour and pattern differences). Where populations are continuous, intermediate specimens also exist, especially in the west. However, even though the result, in terms of appearance, may be a north-south differentiation, the DNA evidence shows very clearly that the story behind it is of an east-west split, and that the two conventional subspecies do not represent separate genetic entities.
Now, I emphasise again that that does NOT mean that anyone says they are indistinguishable. I would agree with Marty's statement that "They've always been seperated in my hot room and always will be" - sure, I'd do the same. I'd also call them "canebrakes" and "timbers". But I would not call them C.h. horridus and C.h. atricaudatus, because that distinction is an artificla one based on a few superficial characters rather than on what evolutionary lineages are actually present within the species.
Cheers,
WW
|
| |
|
RE: Validity of C. horridus atricaudatus
|
Reply
|
|
by Cro on August 21, 2005
|
Mail this to a friend!
|
Wolfgang:
I would have to reluctantly agree with your observations on the non-validity of C.h.atricaudatus as a subspecie. I say reluctantly, as I hate to see all the forms I knew and loved being kicked out, re-named, or elavated by modern taxonomy.
As you and others state, there is a pronounced difference in the appearance, habitat, habits, venom, and behavior of the `Canebrake` form of Crotalus horridus, verses the `Timber` form, but, after reviewing the evidence, I believe, these by themselves are not enough to genetically seperate the Northern and Southern populations as separate subspecie.
This is unfortunate, as any field herper who has encountered both forms of these snakes has clearly seen the morphological and habitat differences, and is lead to conclude that they are different animals.
Your statement that after the ice ages the snakes dispersed and took on different habits and appearances as they dispersed into the new habitats and vegitation zones seems valid. I have observed much difference in the appearance of disjunct populations of Crotalus l. lepidus that are isolated by desert lowlands to specific mountain ranges, where they have evolved patterns to match the local rock colorations and vegation patterns.
You are right in stating that the taxonomity used to seperate subspecie in the 1960`s is outdated with modern DNA and Genetic research, but unfortunatly, people still fall back on old habits and definitions regarding the ability of animals to interbreed or hybridise as a criterion as to subspecification.
As others have stated, I will continue to call a Southern phase timber a Canebrake, and a Northern phase a Timber, even if I label both of them as C. horridus.
Best Regards JohnZ
|
| |
|
RE: Validity of C. horridus atricaudatus
|
Reply
|
|
by Chris_Harper on August 27, 2005
|
Mail this to a friend!
|
WW has effectively "cleared the bar with a pool cue". Wow. Glad I wasn't on the receiving end of that one. There are definitely some bloody teeth on the floor somewhere. ;-)
~CH
|
| |
|
regarding the acceptance of interbreeding.....
|
Reply
|
|
by MattHarris on September 13, 2005
|
Mail this to a friend!
|
...but if its been shown(albeit under captive conditions) that Panterohpis and Lampropeltis can interbreed, of what purpose does this criteria even have in, not even determining subspecies or species, but even in whether its in the same genus????
MCH
P.S. WW, I have saved several shed of Porthidum l. hutmanni and P. l. lansbergi for you. I'll get them in to you shortly.
|
| |
|
RE: Validity of C. horridus atricaudatus
|
Reply
|
|
by longtooth on November 8, 2005
|
Mail this to a friend!
|
|
well i must admit with all that has and has not been done i,m confused on the subject. higher elevations differs the color i have several canes caught in montgomery county nc they are all a beautiful pink granite rock color have some timbers that came from the mts of nc all yellowish or gold with black bands. i have looked at these animals for hrs at a time the ones from montgomery county definantly have a broader head and are far less tempermental than the timbers from the mts.i i have a freind who is cherokee he is from the reservation as far as his people are concerned they are two separate species, but i guess until there is definant proof we will always have to beleive in what we will great topic i love em all nite folks stay safe later longtooth
|
| |
|
Validity of C. horridus atricaudatus
|
Reply
|
|
by coneflower on May 23, 2007
|
Mail this to a friend!
|
|
Is Chad's article saying that Timbers and Canes are two different snakes? The Timber is a listed species, but the Cane does not have its own listing, either Fed or state. After reading many sources on this issue, both for and against the Cane/Timber issue, I am not sure what to believe. Does anyone have current information about this debate?
|
| |
|
RE: Validity of C. horridus atricaudatus
|
Reply
|
|
by LeviathanNI on December 26, 2008
|
Mail this to a friend!
|
|
If only the guy from Indiana had read this he would know all he needs to about this species.. ie no one agrees ergo the status quo remains ie oops
|
| |
|
Email Subscription
You are not subscribed to this topic.
Subscribe!
My Subscriptions
Subscriptions Help
Check our help page for help using
, or send questions, comments, or suggestions to the
Manager.
|
