Posted by:
Wulf
at Fri Nov 5 18:49:47 2004 [ Report Abuse ] [ Email Message ] [ Show All Posts by Wulf ]
Hi folks,
I'm just testing my knowledge 
CKing worte:
There is no doubt about it, the study of phylogeny is best done with molecules, simply because there are so many more molecular characters than morphological ones and because many molecules are selectively neutral whereas morphological characters tend to be adaptive and therefore more likely to be the result of convergent evolution. Nevertheless, phylogeny per se really gives us an incomplete picture.
Well, I agree that there are much more molecular characters than morphological ones, but as you already stated above "Molecular data is of course not infallible" and they might lead to wrong phylogenetic hypotheses.
In his PhD. thesis, B.N. Campbell (1997) examined the molecular phylogenetics of Boidae using the mitochondiral cytochrome b gene. He examined 47 blood samples as well as 143 tissue samples representing 44 species. As a result, Campbell concluded that data from cytochrome b gene were unable to resolve the phylogeny of the Pythonidae in most aspects.
Taggart et al. (2001) also revealed the incongruence between mtDNA and nuclear-DNA data in the genus Bothriechis and concluded that "...the mtDNA results may not reflect specimens relationship..." (Taggart et al., 2001).
As pointed out by Henderson (1997) mtDNA of West Indian taxa of Corallus varies only slightly from Corallus hortulanus, but there is a notable divergence between them in morphologic characters.
So, I would conclude that phylogenetic analysis only on the base of molecular analysis can lead to wrong hyptheses about the phylogeny of species.
There also seems to be still a general methodological problem in molecular systematics. The weighting of data as preferred by some taxonomists may influence phylogenetic relationships. "Subjective" weighting or rejecting of data seems to be more like a "...if they woun't fit, I'll make them fit..." thing and there are several methods to handle data sets used in phylogenetic studies.
Cheers,
Wulf
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