WW wrote:
"Chances are that Henderson's mtDNA phylogeny is spot on: the differentiated island populations are recent derivatives of mainland populations, but which diverged rapidly after getting to the islands - a very common story."

Me:
Sometimes organisms do diverge rapidly when they are stranded on an island. However, rapid divergence does not always occur among populations that are geographically isolated. The California Tiger salamander (Ambystoma tigrinum californiense) for example, is geographically isolated from other subspecies of tiger salamanders and yet it is morphologically very similar to the other populations elsewhere. Reproductive isolation has not evolved, and in fact the courtship behaviors of A. t. californiense and A. t. tigrinum are identical. Introduced tiger salamanders hybridize freely with native tiger salamanders within the range of A. t. calliforniense. Conversely, the lack of geographic isolation has not prevented rapid speciation among the cichlid fishes in the African lakes. As S.J. Gould has often pointed out, evolution cannot be a slow process because environmental changes are not slow. Organisms which change too slowly will not be able to adapt and survive. So, whether rapid divergence will or will not occur really depends on how different the environment on the island may be and whether there are unfilled niches on an island. The lack of mammalian predators on some Indonesian islands has apparently allowed the Komodo dragon to evolve in isolation to fill these niches. Similarly, island tortoises tend to evolve gigantism in the absence of mammalian herbivores.

WW:
"The question of what one does with recently diverged populations like that is a subject of debate, and really down to personal philosophy/preference. Some like to recognise them as separate phylogenetic/evolutionary species due to morphological differentiation and allopatry, others would rather sink them back into the mainland species based on phylogenetic considerations."

Me:
As I have said elsewhere, typological thinking is fashionable. The so-called phylogenetic species and evolutionary species concepts are little more than typological species concepts in disguise. To many taxonomists, species are morphotypes, and therefore when a geographically isolated population has evolved a slightly different morphotype, it is often treated by the typologist as a separate species. Typological thinking is in fact so fashionable that even molecular systematists have adopted it. Some molecular systematists have recognized different mtDNA haplotypes as different species. After these mtDNA "species" have been delimited, the taxonomist then searches for morphological characters with which to define these "species." This was in fact the case in the naming of the southern rubber boa as a different species, although the morphological characters that supposedly define "Charina umbratica" are unreliable. Other systematists have also attempted to delimit genera using mtDNA haplotypes, for example Utiger et al., although they include hemipenial morphology in their analysis. The result is a big mess: a large number of erected/resurrected genera that cannot be defined morphologically nor can they be distinguished from each other morphologically. In fact, Utiger et al. did not even try to define the genera they recognize primarily on the basis of mtDNA haplotypes. These cases of taxonomic chaos could have been avoided if systematists take into accoutn morphological disparity in classifications and if they simply accept paraphyletic taxa as the inevitable result of the process of evolution.

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