Phylogenetic relationships of basal hexapods

Basal hexapods - traditionally called apterygotes - are crucial for understanding the early steps in the evolution of insects as well as for the clarification of their hotly debated relationships to other arthropods. Despite intensive efforts, the phylogeny of the basal hexapods has not yet been unraveled. Numerous competing and controversial hypotheses have been postulated, especially for the entognathous hexapods where both the available morphological and molecular data-sets are not sufficient to clarify their phylogenetic relationships. In this project we will utilize a combined approach to improve the morphological and molecular data-sets of the most relevant entognathous hexapod taxa (Protura, Collembola and Diplura). Data from the literature concerning the outgroups will be used for comparative purposes, however we intend to significantly enhance this information by authentic analyses of certain myriapod taxa. Our morphological investigations will encompass a number of character systems that have not yet been extensively investigated in a phylogenetic context. Furthermore, a critical re-evaluation and re-investigation of published data are necessary. We refer especially to the circulatory and tracheal systems, the internal structure of the thorax, abdomen (endoskeleton and musculature) and abdominal appendages. In the molecular investigations several markers will be included that have proved phylogenetically informative for the given time scale. These are highly conserved nuclear ribosomal (18S and 28S) and protein-coding (EF1-a, EF2, PolII) genes, as well as the sequences and gene order of the complete mitochondrial genome. The data obtained from both approaches will be used in separate and combined phylogenetic analyses. We expect to obtain results highly relevant for the elucidation of relationships within basal hexapods and their position with respect to ectognathous insects. In addition, the significance of the data will be discussed with regard to the phylogenetic position of hexapods to other major groups of arthropods.

Basal hexapods - traditionally called apterygotes - are crucial for understanding the early steps in the evolution of insects as well as for the clarification of their hotly debated relationships to other arthropods. Despite intensive efforts, the phylogeny of the basal hexapods has not yet been unraveled. Numerous competing and controversial hypotheses have been postulated, especially for the entognathous hexapods where both the available morphological and molecular data-sets are not sufficient to clarify their phylogenetic relationships. In this project we will utilize a combined approach to improve the morphological and molecular data-sets of the most relevant entognathous hexapod taxa (Protura, Collembola and Diplura). Data from the literature concerning the outgroups will be used for comparative purposes, however we intend to significantly enhance this information by authentic analyses of certain myriapod taxa. Our morphological investigations will encompass a number of character systems that have not yet been extensively investigated in a phylogenetic context. Furthermore, a critical re-evaluation and re-investigation of published data are necessary. We refer especially to the circulatory and tracheal systems, the internal structure of the thorax, abdomen (endoskeleton and musculature) and abdominal appendages. In the molecular investigations several markers will be included that have proved phylogenetically informative for the given time scale. These are highly conserved nuclear ribosomal (18S and 28S) and protein-coding (EF1-a, EF2, PolII) genes, as well as the sequences and gene order of the complete mitochondrial genome. The data obtained from both approaches will be used in separate and combined phylogenetic analyses. We expect to obtain results highly relevant for the elucidation of relationships within basal hexapods and their position with respect to ectognathous insects. In addition, the significance of the data will be discussed with regard to the phylogenetic position of hexapods to other major groups of arthropods.