Taxonomic publications: past and future - Senckenberg Museum

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Burckhardt & Mühlethaler (eds): 8 th GfBS Annual Conference Abstracts 50 Advances in phylogenetic inference from molluscan mitochondrial genomes Gerhard Steiner, Hermann Dreyer, Miriam Satler, Martina Knapp The use of complete mitochondrial genomes – both their nucleotide sequences and the gene arrangements – for phylogenetic inference has steadily increased during the past years. Although the Mollusca are the most species-rich phylum second to Arthropoda, there are only 20 complete molluscan mitochondrial genomes published compared to about 100 arthropod and almost 500 vertebrate genomes. This low number may result from peculiarities of molluscan mt-genomes that make them difficult to analyze. Genome size and gene order vary considerably among molluscs. Gene duplications and, at least in bivalves, heteroplasmy due to distinct female and male mt-genome lineages (doubly uniparental inheritance) complicate template generation, sequencing and phylogenetic analyses. As a consequence, the molluscan taxon sample has been insufficient to recover plausible phylogenies from mt-gene order data. We present 12 additional mt-genomes, ten from Bivalvia and one each from Scaphopoda and Caudofoveata respectively, with the main purpose to assess gene order variability within bivalves. The trees resulting from parsimony and Bayesian analyses of amino acid sequence data show a well supported cephalopod clade but the other major taxa appear diphyletic. This is caused by the most basally branching species in each taxon, Nucula (Bivalvia), Haliotis (Gastropoda), and Graptacme (Scaphopoda) clustering together with the polyplacophoran Katharina and the caudofoveate Chaetoderma at the base of the molluscan subtree. Similar topologies result from the parsimony and Bayesian analyses of gene order data with the same species in a basal position due to their conserved plesiomorphic gene order. The corresponding positions of these species in the amino acid and gene order trees suggest similar substitution and rearrangement rates. This is corroborated by the significant correlation of the relative change rates of both parameters, as has previously been shown also for mt-genomes of Hexapoda. With a near-plesiomorphic gene order present in most major molluscan groups, accelerated rearrangement rates must have arisen independently within each group. However, we can show that the improvement of the taxon sample increased the quality and reliability of phylogenies inferred from mt-genomes. Especially in fast evolving taxa as the bivalves, these data hold great promise to resolve their deep phylogeny when more mt-genomes become available. Supported by the Austrian Science Fund, FWF project P16954-B12. Org. Divers. Evol. 5, Electr. Suppl. 13 (2005)
Burckhardt & Mühlethaler (eds): 8 th GfBS Annual Conference Abstracts 51 Applications of DNA barcoding D. Steinke, M. Pfenninger & A. Meyer According to Ernst Mayr, the first task of a taxonomist is to “sort that portion of the diversity of the individuals which he encounters into easily recognisable and internally homogeneous groups, and to find constant differences between such groups”. In a second step, the identified groups he called “phena” can be assigned to species, either already known to science or not, based on the degree of reproductive isolation to other such groups. The aim of the recently proposed framework of DNA-taxonomy is to find such “phena”, sometimes called Molecular Defined Operational Taxonomic Units (MOTU) on the basis of sequence differences at short, orthologous marker gene sequences. This follows the general definition of Operational Taxonomic Units (OTU) as groups of organisms used in a taxonomic study without designation of taxonomic rank. Just as in traditional taxonomy, MOTUs do not necessarily equate to biological species, but should be treated rather as taxonomical hypotheses in need for additional evidence of their reproductive isolation. The conceptual slightly different approach of DNA-barcoding tries to assign unknown specimen to known taxa with the aid of the same type of widely applicable markers used. Presently, some controversy exists over the value of DNA barcoding. It has been raised that this identification method would diminish rather than improve traditional morphologybased taxonomy. Critics argue that species determinations based solely on the amount of genetic divergence could result in incorrect species recognition, although the concept of MOTUs is taking this into account. It has also been stated that DNA barcoding is a means to reconstruct phylogenies when it is actually a tool to be used largely for identification purposes. Practical assets of DNA taxonomy approaches and tools to use DNA barcodes will be reviewed in this talk. In addition we will introduce a statistical approach to derive distance thresholds for MOTU identification empirically from the data. Currently, ‘rules of thumb’ are employed to delineate MOTUs on the basis of sequence divergences. These ‘rules of thumb’ are derived from comparing intraspecific versus interspecific variation in taxa where species borders assumed to be well known. In zoology, this assumption may be met for certain vertebrate taxa; for the majority of biodiversity, however, it is certainly not. Therefore, in order to obtain reliable, objective thresholds for MOTU delineation in various taxa, the effort should not necessarily focus on whether a given marker can resolve an existing taxonomy, but rather whether this marker can resolve the individuals under scrutiny into statistically supported MOTUs. Org. Divers. Evol. 5, Electr. Suppl. 13 (2005)
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