PhyloCode und DNA Barcoding - Taxonomische Regeln und Techniken im Wandel?

Abstract

The terms PhyloCode and DNA Barcoding represent novel, strongly debated developments of high significance to taxonomy (systematics) and directly linked disciplines like biogeography. The PhyloCode has been set up as an international code of phylogenetic nomenclature. Its goals comprise the introduction of a taxonomic system which builds on the phylogenetic relationships and which is universally applicable to all organisms. Existing codes such as the International Code of Zoological Nomenclature (ICZN) are character-based and rank-based and hardly allow conclusions on phylogenetic relationships. The PhyloCode establishes rules for applying names to clades and deliberately excludes information on the relative rank of clades. The advocates of the PhyloCode highlight a said stability of names contrasting with the denied continuity of nomenclature of traditional codes. This statement neglects that “specifiers” of clades are no longer valid once a supposed synapomorphy is recognized to be actually a homoplasy. Checks of further properties of the PhyloCode did not reveal demonstrable advantages over existing codes like the ICZN. The latter has shortcomings concerning the consideration of recent findings of phylogenetic research. This is by far outweighed by the fact that the underlying principle of the ICZN proved to be applicable as a mandatory code for 100 years and in agreement with all the scientific progress during 250 years. DNA Barcoding is a method for using a small section of DNA to characterize all extant species. The resolution of the mitochondrial COI sequence and its storage in a data bank has been proclaimed to allow the unambiguous characterization and identification of all organisms. Supposedly, this should be a more efficient method to recognize and register the taxonomic biodiversity on earth when compared to the mostly non-molecular methods of traditional taxonomists. It turns out, however, that the base sequence analysis of COI of actually all species is a utopian goal. An unambiguous identification seems hardly possible in all cases because of a certain variability in the base sequences. COI analyses form one part of the molecular techniques and methods used by taxonomists for several years in addition to traditional methods. Thus, any effort to enhance COI analyses results in an addition to the knowledge on taxonomic diversity. Taxonomists working in an integrative manner by combining traditional and molecular methods are well aware that only a combination of several molecular and traditional methods contributes to a progress in revealing taxonomic diversity. Among the main goals of DNA Barcoding is the automated identification of taxa. Currently, this does not seem to be generally possible with an unambiguous result and, therefore, the whole range of molecular and traditional techniques will continue to be required for the characterization and identification of species.

Keywords

clade, DNA Barcoding, DNA taxonomy, ICZN, PhyloCode, phylogenetics, molecular systematics.