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Phylogeny and evolution of Monoplacophora and Mollusca
Phylogeny and evolution of Monoplacophora and Mollusca
The Mollusca comprises eight classes which are highly diverse in their morphology as well as in molecular appearance. The class level relationships in molluscs were hotly debated during decades and are still under discussion as there is no overall support for one single concept. Morphological and recent phylogenomic studies support the hypothesis of Aculifera (Solenogastres, Caudofoveata and Polyplacophora) and summarize Bivalvia, Cephalopoda, Gastropoda, Monoplacophora and Scaphopoda as the Conchifera. Alternative concepts as Testaria (Bivalvia, Cephalopoda, Gastropoda, Monoplacophora, Scaphopoda and Polyplacophora) or Serialia (Monoplacophora + Polyplacophora) were suggested in the past based on morphological analyses (Testaria) or mainly molecular evidence (Serialia). In order to bring resolution to the class relationships and the early evolution within Mollusca we compiled several comprehensive taxon sets comprising different molecular datasets: combined nuclear and mitochondrial markers obtained via Sanger sequencing (“standard markers”), mitochondrial genomes (analyzing the phylogenetic information of the sequence data as well as comparing the gene arrangements) and phylogenomic data obtained via Next Generation Sequencing. We were able to generate novel data of several species of the elusive class Monoplacophora. Based on the set of standard markers, we found support for Serialia whereas the phylogenomic approach leads to Aculifera and Conchifera, providing first molecular evidence for Monoplacophora sister to Cephalopoda plus other conchiferans; a clade of Gastropoda and Scaphopoda is also supported. Both phylogenetic analyses were used for time estimations and resulted in congruent ages for the molluscan stem (Precambrian) and the diversification of Mollusca (584Mya). We were the first to present a complete mitochondrial genome of a monoplacophoran species ever. Analyzing the mitochondrial gene arrangements we were able to detect potential synapomorphies for Mollusca. Standard marker analyses on comprehensive taxon sets provided novel phylogenetic hypotheses on several molluscan subgroups, such as chitons and gastropods, in particular heterobranchs, challenging mitogenomic approaches and results in the latter. Overall, our studies addressed the phylogeny and evolution of Mollusca and subgroups with a variety of markers and methods and helped to pave the way from using multilocus markers and mitogenomics towards whole genomes.
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Stöger, Isabella
2021
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Stöger, Isabella (2021): Phylogeny and evolution of Monoplacophora and Mollusca. Dissertation, LMU München: Faculty of Biology
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Abstract

The Mollusca comprises eight classes which are highly diverse in their morphology as well as in molecular appearance. The class level relationships in molluscs were hotly debated during decades and are still under discussion as there is no overall support for one single concept. Morphological and recent phylogenomic studies support the hypothesis of Aculifera (Solenogastres, Caudofoveata and Polyplacophora) and summarize Bivalvia, Cephalopoda, Gastropoda, Monoplacophora and Scaphopoda as the Conchifera. Alternative concepts as Testaria (Bivalvia, Cephalopoda, Gastropoda, Monoplacophora, Scaphopoda and Polyplacophora) or Serialia (Monoplacophora + Polyplacophora) were suggested in the past based on morphological analyses (Testaria) or mainly molecular evidence (Serialia). In order to bring resolution to the class relationships and the early evolution within Mollusca we compiled several comprehensive taxon sets comprising different molecular datasets: combined nuclear and mitochondrial markers obtained via Sanger sequencing (“standard markers”), mitochondrial genomes (analyzing the phylogenetic information of the sequence data as well as comparing the gene arrangements) and phylogenomic data obtained via Next Generation Sequencing. We were able to generate novel data of several species of the elusive class Monoplacophora. Based on the set of standard markers, we found support for Serialia whereas the phylogenomic approach leads to Aculifera and Conchifera, providing first molecular evidence for Monoplacophora sister to Cephalopoda plus other conchiferans; a clade of Gastropoda and Scaphopoda is also supported. Both phylogenetic analyses were used for time estimations and resulted in congruent ages for the molluscan stem (Precambrian) and the diversification of Mollusca (584Mya). We were the first to present a complete mitochondrial genome of a monoplacophoran species ever. Analyzing the mitochondrial gene arrangements we were able to detect potential synapomorphies for Mollusca. Standard marker analyses on comprehensive taxon sets provided novel phylogenetic hypotheses on several molluscan subgroups, such as chitons and gastropods, in particular heterobranchs, challenging mitogenomic approaches and results in the latter. Overall, our studies addressed the phylogeny and evolution of Mollusca and subgroups with a variety of markers and methods and helped to pave the way from using multilocus markers and mitogenomics towards whole genomes.