I wrote:

`The claim that Utiger et al. delimited Elaphe on the basis of morphological disparity is unsupported.'



You wrote:

Weakly supported, I'd say, but either way, the claim that the taxa they created are `morphologically indistinguishable' is also unsupported.



My response:

You seem to be contradicting yourself. Your words "also unsupported" seem to be an acknowledgement that your claim is unsupported and that my claim is also similar to your unsupported claim. But you also claim that it is "weakly supported." Either it is unsupported or supported (albeit weakly). It cannot be both weakly supported and unsupported.



I wrote:

`I am not sure what you mean, but as I said, all of the species of Elaphe in Lopez and Maxson are more closely related to each other than they are to Ptyas or any other racer.'



Your response:

Agreed. The problem, as I mentioned, is that they have very few species of Elaphe sensu lato to work with, and can't draw any conclusions about Elaphe sensu lato as a whole.



My response:

It is true that they do not have all species of Elaphe in their study. It is a weakness they themselves acknowledge. But their study does include both New World and Old World species of Elaphe. Both groups are more closely related to each other than either one is to Ptyas in Lopez and Maxson's study. Utiger et al. find the same thing. Utiger et al. also find Elaphe mandarina (along with E. conspicillata) to be the most basal lineage within Elaphe. Tong et al. (Acta Zoologica Sinica) find the same things Utiger et al. do: E. mandarina is the most basal member of Elaphe and Ptyas is an outgroup. Tong et al. also finds a bootstrap value of 98 for the split between Ptyas and Elaphe.



I wrote:

`You are suggesting that a difference in the amount of statistical support for Ptyas as an outgroup between the two studies is evidence of polyphyly of Elaphe?'



Your response:

Not just a difference, but, specifically, the correlation between increased in-group represenation and decreased support for the out-group's position.



My response:

I suggested that there may be something wrong with Utiger et al.'s data. You disagreed.



I wrote:

`That is an unsupported interpretation of the available data. '



You wrote:

It's just common sense. Low outgroup support implies differences in relatedness between the out-group and different members of the in-group. If your in-group members are all closely related, out-group support should be high. If out-group support is low, probably the outgroup is either very closely related to all of the in-group taxa (which is argued against by the much higher outgroup support of Lopez and Maxson's study) or your in-group contains fairly divergent taxa, some of which are fairly closely related to the outgroup, and some of which aren't. It's not great evidence of polyphyly, but my main reason for mentioning it was that it's a more plausible explanation for the

differences in out-group support than your offhand conclusion that it must indicate some problem with Utiger et al.'s data. Which, by the way, seems to be an `unsupported interpretation'.



My response:

It is not common sense. Low outgroup support could also mean that there is adaptive radiation at that node, which could result in an unresolved polytomy. Unresolved polytomies can also be the result of uninformative characters. As you admit, Lopez and Maxson's findings clearly shows that Ptyas is an outgroup. So does Utiger et al.'s tree. Now Tong et al. (Acta Zoologica Sinica) have shown that Ptyas is an outgroup to all of the species of Elaphe they study, including the most basal member (E. mandarina), there can be little doubt that Elaphe is not polyphyletic (Darwinians will wonder why I choose to say "not polyphyletic" instead of "monophyletic." I do so because I want to obviate the typical Hennigian tactic of erecting a red herring argument by engaging in semantic arguments about the meaning of monophyletic, a term that they hijacked from the Darwinians).



I wrote:

`The only way Elaphe can be polyphyletic is if some of them form a clade with Ptyas to the exclusion of other species of Elaphe. Neither Lopez and Maxson nor Utiger et al.'s data shows that. Tong et al.'s study also include Ptyas. Like the other two studies, theirs also show Ptyas outside of the Elaphe clade.'



Your response:

This has already been addressed.



My response:

That is a weak response. Your slim hope that Utiger et al.'s data somehow suggest that Elaphe is polyphyletic has been dashed by Tong et al.'s bootstrap value of 98 for the Ptyas-Elaphe split.



I wrote:

`You are obviously influenced by Utiger et al.'s single sentence on page 105, in which they claim that several authors "...concluded that Elaphe auct. as presently understood represents a large polyphyletic group." One of the papers they cite is that of Dowling et al. (1983). Dowling et al. do not include any of the Old World Elaphe species in their study. Therefore they have no data to show that Elaphe is polyphyletic; they are merely speculating'



Your response:

Very good. So if you're willing to make the argument that an insufficient number of taxa can prevent conclusions about a genus as a whole here, why do you reject it in reference to Tong et al.'s and

Lopez and Maxson's studies?



My response:

No, I am not making that argument. I am arguing that Dowling et al. do not include any species of Old World Elaphe in their study and therefore they have no evidence to support the speculation that Old World and New World Elaphe form a polyphyletic group. They have to include at least one species from each group to demonstrate that. This is clearly not the case with Lopez and Maxson's study, who includes several species of Old World and several species of New World Elaphe. They find that Old World and New World Elaphe are part of a monophyletic group that excludes Ptyas. Further, they find that New World Elaphe is a derived group and that Old World Elaphe is basal. Utiger et al. rectify the shortcomings of Lopez and Maxson and includes a lot more species. They, too, find that Old World and New World Elaphe are part of a monophyletic group and that New World Elaphe is derived and Old World Elaphe is basal. Tong et al. do not include any New World species of Elaphe, but they show that Ptyas is an outgroup of Old World Elaphe, including the most basal member E. mandarina. These 3 studies conclusively show that Ptyas is an outgroup to Elaphe.



You wrote:

And I think that leaves us still with four papers concluding that Elaphe sensu lato is polyphyletic.



My response:

Then it is up to you to dig them out to prove that Elaphe is polyphyletic.



I wrote:

`Tong et al. (2002) also conclude that Dessauer (another paper cited by Utiger et al.) assumes that Elaphe is polyphyletic.'



You wrote:

Correct me if I'm wrong, but as far as I know we still don't know either what Tong et al.'s reasons for coming to this conclusion are, or even if Utiger et al. and Tong et al. are referring to the same paper.



My response:

Both Utiger et al. and Tong et al. cite Dessauer et al. 1987. "Patterns of snake evolution suggested by their proteins," Field. Zool. New Ser. 34:1-34



As for the reason Tong et al. claim that Dessauer [et al.] is assuming that Elaphe is polyphyletic, it is obvious that if one has no evidence, then one is merely making an assumption.



I wrote:

` Further, Utiger et al. fail to cite Lopez and Maxson (1995), which clearly shows that Elaphe is a monophyletic group (paraphyletic if the Lampropeltini is excluded).'



Your response:

This has already been addressed.



My response:

That is not much of a response. A weak response but still a response.



I wrote:

`It appears that Utiger is including studies that speculate on the polyphyly of Elaphe and at the same time overlooking those that refutes polyphyly. If that is the source of your "multiple independent

studies concluding that Elaphe...is polyphyletic," then you have been misled by Utiger et al.'



Your response:

Interestingly, Utiger et al. also cite Lenk et al. (mentioned elsewhere in this thread) but do not mention that Lenk et al. conclude that Elaphe sensu lato is polyphyletic. There doesn't appear to be a bias in regards to their citation on the matter. Furthermore, which papers they've chosen to cite doesn't influence the validity of the papers they've cited. There are indeed multiple independent studies concluding that Elaphe sensu lato is polyphyletic, whether Utiger et al. may have failed to cite other studies (whether they support the opposite conclusion or not) or not.



My response:

Utiger et al. cite 4 papers. One of these (Dowling et al.), as I point out, cannot possibly make that conclusion since it does not include a single species of Old World Elaphe in it. A second paper (Dessauer et al. 1987) is claimed by Tong et al. to have made an assumption for Elaphe polyphyly. A third study (Dessauer 1983) predates the 1987 assumption (interestingly, Utiger et al. neglect to give the full citation for this paper). So the only unrefuted (by me) study that Utiger et al. cites for Elaphe polyphyly is Minton (1976, Serological relationships among some congeneric North American and Eurasian colubrid snakes. Copeia 1976:672-678)



You are on thin ice indeed if Minton's 1976 paper is your only unread evidence of a polyphyletic Elaphe, especially since Utiger et al.'s own study (as well as that of Lopez and Maxson and Tong et al.) refutes Elaphe polyphyly.



I wrote:

`You may disagree all you want, but if your disagreement is unsupported by scientific evidence, then it is a meaningless disagreement.'



Your response:

If we'll accept the converse implication, it would appear my disagreement is not meaningless.



Patrick Alexander



My response:

To give it meaning, you must submit evidence for a polyphyletic Elaphe. So far the best you can do is your assumption that the four papers cited by Utiger et al. prove that, and your weak argument that the low bootstrap value for Ptyas as outgroup in Utiger et al. suggest possible polyphyly. That is skating on very thin ice indeed. Or perhaps you are actually skating on the surface tension of the water molecules.

[ Show Entire Thread ]