>>CK,
>>The current researcher mentioned something to the effect that the relationship between the Rosy, Calabar, and Rubber Boa are different from what Javier portrayed them in his mtDNA paper.>>

Rodriguez-Robles et al. did treat the Rosy boa as an outgroup a priori. They never considered the possibility of budding evolution, i.e. that the Rosy boa evolved from one population of the rubber boa, while the rubber boa remained a distinct species that is relatively unchanged.

>>Also, what information tells you that it was the Rosy Boa that evolved from the Rubber Boa and not the reverse? And isn't there the possibility that both species arose from some common ancestor?>>

One basic assumption that cladists such as Rodriguez-Robles make is that speciation occurs exclusively via the process of splitting. Splitting occurs when one ancestral species give rise to 2 daughter species. Budding, however, occurs when one species continues to live relatively unchanged, while one or more new species budded off the ancestral species. The cladists, when pressed, often admit that they don't really believe in splitting, and even Hennig (the father of cladism) himself admits that their assumption of splitting is only a "convention." Cladists sometimes call budding "asymmetric splitting" (meaning that one sibling species evolved far more than the other sibling species and also meaning that cladists are unable to divorce themselves from their own dogma). Cladists justify their intolerance of paraphyletic groups in their classification by asserting that splitting is the predominant means of how new species are formed (even though they then admit that splitting is only a convention). Darwinians, however, maintain that most species are formed by peripatric speciation, in which a small isolated population evolved rapidly into another species while the larger parental population remain relatively unchanged. The old species continues to live and it is paraphyletic. Similarly, higher taxa evolved the same way. A new higher taxon evolves via budding from an exiting higher taxon, thus rendering the parental taxon paraphyletic. Hence paraphyletic taxa are the natural consequence of the process of evolution and they should not be eliminated, despite the cladists' dogmatic intolerance.

Most evolutionary biologists would agree that most new species probably evolved via peripatric speciation or budding, although quite recently it has been demonstrated that sympatric speciation is also quite common. What the cladists assume is that speciation occurs mostly via allopatric speciation, in which two geographically isolated populations evolve into two different species gradually over time and neither species is the same as the parental species.

What leads me to believe that the rosy boa evolved from the rubber boa but not vice versa? One reason is the Mojave Desert. The rosy boa inhabits the Mojave Desert and it is superbly adapted to the desert. The Mojave Desert at one point in time did not exist. This is obvious if we look at the distribution of the rubber boa, because the Kern County rubber boas and the southern rubber boa were once part of the same population. mtDNA divergence between the northern and southern subclades have shown that they have been isolated from each other for approximately 5-12 million years according to Rodriguez-Robles et al. Morphologically they have remained relatively unchanged, making the rubber boa a good candidate as the parental species from which the Rosy boa budded off. The morphological similarities between the Kern County and Southern Rubber boas also argue against splitting, because when splitting occurs, both sibling species are very different from the ancestral species. Since the rubber boa remained largely unchanged, it is difficult to argue that splitting is the speciation mechanism between the rubber and rosy boas. Further, if the rosy boa is ancestral, then the rubber boas from Kern County northward and the southern rubber boa evolved convergently and independently from a desert adapted species into 2 morphologically similar inhabitants of moist woods. It is of course possible, but very unlikely.

Yet another clue that the Mojave Desert is younger than the rubber boa is the distribution of Lampropeltis zonata. The range of L. zonata is interrupted by the Mojave Desert, and yet there are L. zonata found both north and south of this desert, suggesting that the range of L. zonata was also continuous before the formation of the Mojave Desert.

>>Correct me if I am mistaken but I believe you have mentioned that mtDNA results provide a clue to the age of various lineages. So if that is correct, taking in account the explanation
>>for Fig. 4 in the Rodriguez-Robles paper along with the relative lengths of the arms of his ML tree, can it be inferred:
>> 1) That the Southern Clade is older than the Northern Clade and that the latter arose from the former? (You have already stated this before.)

Yes and no. The southern subclade consists of a number of genetically similar populations that appear to have only diverged from one another very recently. Yet, the southern subclade as a lineage is quite old, and the mtDNA marker that the southern and northern subclades share is an ancient one. So, even though the northern subclade is derived from a population that lived in the south, the northern subclade is not descended directly from one of the living populations in the South. However, the morphological similarities between the southern rubber boa and the Kern County small morph boas suggest that neither have diverged morphologically from their common ancestor. So we can safely say that the northern subclade evolved from the southern rubber boa and that the southern rubber boa is closest to the ancestral morphotype of the species.

>> 2) That the Northwestern subclade is older than the Sierra Nevada subclade?

No. That is not the case. Both subclades evolved from a common ancestor subsequent to the split between northern and southern rubber boa subclades. This ancestor is almost certainly a small morph snake. However, what I have maintained is that the Northwestern subclade, which is large morph, evolved the large morph genotype much earlier than the large morph snakes evolved within the Sierra Nevada subclade. Currently the Sierra Nevada subclade includes a mixture of both older small morph populations and younger large morph boas. I have suggested that the small morph snakes within the Sierra Nevada subclade be classified with umbratica in the same subspecies, and the large morph Sierra Nevada boas be classified in its own subspecies, while the Northwestern subclade will be the third subspecies in a 3 subspecies arrangement.

>> 3) That samples 15, 17, 18, 19, and 26 are older than all other tested samples of the Sierra Nevada subclade?

No, that is not exactly what the mtDNA data shows. The mtDNA data shows that these snakes form a lineage, and this lineage is older than the lineage that is comprised of the Kern County small morph boas and the Central Sierra Nevada large morph boas (south of samples 17,18,19 but north of Kern County. However, mtDNA shows that these samples also diverged from one another quite recently. So it appears this old lineage may have arrived relatively in its present location relatively recently. That of course means the possibility of a trans-Valley leak cannot be ignored.

>> 4) That sample 26 is the oldest member of the Sierra Nevada subclade?
>>
>>Richard F. Hoyer

No, Richard. The sample 26, according to the ML tree, is slightly younger than the lineage that gave rise to the Plumas, Butte and Nevada County boas, which are in turn older (as a lineage) than the other Sierra Nevada subclade boas. That is the main reason I think the ancestor of the Butte, Nevada and Plumas County snakes may have been small morph. In fact, one can include sample 26 and the Plumas, Butte and Nevada County boas as part of a paraphyletic northwestern subclade separate from the Sierra Nevada subclade. You raised some very interesting questions that I did not even consider.

[ Reply To This Message ] [ Subscribe to this Thread ] [ Show Entire Thread ]