Are the Hexapoda monophyletic?

The intensive efforts of the last years to elucidate the major arthropod relationships produced a number of conflicting hypotheses. An especially hotly debated point is the phylogenetic position of the Hexapoda. Of special interest in this debate are the basal hexapod lineages, which were traditionally termed apterygotes. Recent investigations on mitochondrial genes, suggest that some of these groups are not closely related to hexapods. According to this interpretation, Hexapoda would not be monophyletic and the tripartite body organization, along with hexapody, must be the product of convergent evolution. The clarification of these important phylogenetic issues necessitates an integrative approach, based on both molecular and morphological data. Therefore our research group has organized a network of international cooperation partners. The advance of this initiative is the construction of a big data set on a joint comprehensive taxon sampling regime. The resulting increased comparability allows for causal explanations of conflicts between different phylogenetic hypotheses. In our project we will analyse data from both gene sequences and organ systems of hexapods, crustaceans and myriapods. Genes widely used in phylogenetic studies will be complemented by new genes, as well by a genomic approach, the so called EST-analyses. The comparative analysis of organ systems will mainly focus on the thorax, the most important constitutive character of insects, and the brain. The comprehensive results will be a major step in the understanding of arthropod phylogeny and will provide crucial insights into the evolution of the most successful animal group on earth. The results are important in all fields of insect research, where interpretations are based on a broader evolutionary background.

The intensive efforts of the last years to elucidate the major arthropod relationships produced a number of conflicting hypotheses. An especially hotly debated point is the phylogenetic position of the insects or hexapods. Which are their closest relatives among arthropods and how are the relationships among the basal hexapod lineages, which were traditionally termed apterygotes? Investigations on mitochondrial genes, even suggest that some of these groups are not closely related, which would mean that hexapods are not monophyletic. The clarification of these important issues in animal phylogeny necessitates an integrative approach based on both molecular and morphological data, which can only be provided by the collaboration of a number of experts. During the period of the project the initiative 1KITE (1K transcriptome evolution) was started, in which our team cooperates with more than 50 scientists from 8 nations (http://www.1kite.org/). We were strongly involved in the conception and organization of this big research initiative which aims to reveal a robust phylogenetic tree of insects.Our two large phylogenomic analyses, in which about 1000 genes were used, revealed both the monophyly of hexapods. With respect to the origin of hexapods the new hypothesis, that crustaceans and not myriapods are the closest relatives among arthropods, was strongly supported. The crustacean group Remipedia was found to be the most probable sister group of hexapods. With respect to the early splits among hexapods our two phylogenomic analyses revealed remarkably contradictory results. The deeper analysis of these conflicts made our study a prime example to study the problems with resolving very old splits in phylogenetic trees which is of relevance for phylogenetic studies in general. The morphological approach focussed on the phylogenetic analysis of characters of the head, the brain and various extremities.In conclusion, our comprehensive investigations represent a major step forward in a deeper understanding of arthropod phylogeny and provide crucial insights into the evolution of the most successful animal group on earth. The results are important in all fields of insect research, where interpretations are based on a broader evolutionary background.