Assessment of the gene order diversity in the mitochondrial genomes of Bivalvia (Mollusca) and its significance for phylogenetic inference

Mitochondria are organelles of eukaryotic cells functioning as "power stations" by facilitating oxidative phosphorilation. They possess a small, extra-nuclear genome which is usually strictly maternally inherited. Most animal mitochondrial (mt) genomes contain 37 genes encoded on a ring-shaped DNA molecule. The gene order on this ring is highly conserved in the well studied vertebrates and arthropods. Thus, the rare rearrangements are highly valuable characters in phylogenetic analyses. In Mollusca, the most species-rich phylum next to Arthropoda, mt-genomics still is in its infancy. However, the ten known mt-genomes exhibit greater diversity in gene arrangement than those of other phyla. Whereas the basal taxon Polyplacophora and the highly derived Cephalopoda have gene orders comparable to other invertebrates like Arthropoda, Annelida or Brachiopoda, that of Scaphopoda and Bivalvia appear extensively altered. Apparently, rearrangement frequencies are drastically higher in these groups than in Polyplacophora or Cephalopoda. The Bivalvia, with four mt-genomes known, feature more peculiarities than completely altered gene orders. The most spectacular is perhaps the "Doubly Uniparental Inheritage" (DUI) of the distinct female and male mt-genomes. The male-type is passed on only from the father to its male offspring, but the female-type is passed on to both sexes. All four bivalve species known for the complete mt-genomes, although systematically not closely related, show this type of inheritance. Furthermore, all these bivalves lack the ATPase8 gene in their mt-genomes; several tRNA genes have unusual secondary structures; and finally, the longest mt-genomes are found in bivalves. The usual mt-genome size is about 17000 base pairs (bp). In the familiy Pectinidae, however, mt-genome sizes of up tp 40000 bp occur. The aim of this project is to assess the systematic distribution and the phylogenetic significance of these genomic characters descibed above. Additional 15 bivalve mt-genomes will help to unravel the diversity of mt-gene order, and also the systematic level this character contains phylogenetic signal. Orthodox and new methods in amplification of genomes (Long-Range- PCR, Rolling-Circle-Amplification) will be used to achieve this task. The data to be generated do not only contain gene order information that are of phylogenetic significance, but also sequence data aiding to the phylogenetic data set of the Bivalvia. Both data types will be used to gain deeper insights into the phylogenetic patterns and the evolution of Bivalvia.

Mitochondria are organelles of eukaryotic cells functioning as "power stations" by facilitating oxidative phosphorilation. They possess a small, extra-nuclear genome which is usually strictly maternally inherited. Most animal mitochondrial (mt) genomes contain 37 genes encoded on a ring-shaped DNA molecule. The gene order on this ring is highly conserved in the well studied vertebrates and arthropods. Thus, the rare rearrangements are highly valuable characters in phylogenetic analyses. In Mollusca, the most species-rich phylum next to Arthropoda, mt-genomics still is in its infancy. However, the ten known mt-genomes exhibit greater diversity in gene arrangement than those of other phyla. Whereas the basal taxon Polyplacophora and the highly derived Cephalopoda have gene orders comparable to other invertebrates like Arthropoda, Annelida or Brachiopoda, that of Scaphopoda and Bivalvia appear extensively altered. Apparently, rearrangement frequencies are drastically higher in these groups than in Polyplacophora or Cephalopoda. The Bivalvia, with four mt-genomes known, feature more peculiarities than completely altered gene orders. The most spectacular is perhaps the "Doubly Uniparental Inheritage" (DUI) of the distinct female and male mt-genomes. The male-type is passed on only from the father to its male offspring, but the female-type is passed on to both sexes. All four bivalve species known for the complete mt-genomes, although systematically not closely related, show this type of inheritance. Furthermore, all these bivalves lack the ATPase8 gene in their mt-genomes; several tRNA genes have unusual secondary structures; and finally, the longest mt-genomes are found in bivalves. The usual mt-genome size is about 17000 base pairs (bp). In the familiy Pectinidae, however, mt-genome sizes of up tp 40000 bp occur. The aim of this project is to assess the systematic distribution and the phylogenetic significance of these genomic characters descibed above. Additional 15 bivalve mt-genomes will help to unravel the diversity of mt-gene order, and also the systematic level this character contains phylogenetic signal. Orthodox and new methods in amplification of genomes (Long-Range- PCR, Rolling-Circle-Amplification) will be used to achieve this task. The data to be generated do not only contain gene order information that are of phylogenetic significance, but also sequence data aiding to the phylogenetic data set of the Bivalvia. Both data types will be used to gain deeper insights into the phylogenetic patterns and the evolution of Bivalvia.