MOLMORPH · Evolution of animal body plans as inferred by developmental biology, morphology, molecular phylogeny, and palaeontology

Final Activity Report Summary - MOLMORPH (Evolution of animal body plans as inferred by developmental biology, morphology, molecular phylogeny, and palaeontology)

The network tackled a number of scientific questions concerning the evolution and interrelationship of metazoan animals as well as the morphology of the last common ancestor of bilaterians. The projects on segmentation revealed that this was a variable ontogenetic process that might be lost over evolutionary time. The muscular anatomy of the most basal bilaterians and therefore, potentially, of the last common ancestor of bilateria was much more complex than previously believed. Neural development showed that, despite the plexus-like, little concentrated neural anatomy of adult acoels, juveniles showed a concentration of transcripts of a neural patetterning gene in the anterior region. This suggested that basal bilaterians already had a concentration of expression of neural genes in the anterior region that became the 'brain' in higher groups. Analysis of the microscopic anatomy of the juvenile stage revealed that some acoels indeed had a true, compact brain which was in contradiction with previous hypothesis. A molecular approach to the central nervous system (CNS) development resulted in numerous antibodies which were subsequently applied to embryos. In addition, the regeneration capacity of s. roscoffensis was studied by sectioning adult individuals in half and following the fate of both fragments. Both halves regenerated completely into morphological and functional adults. We mapped the location of many cell types in the blastema during the entire regeneration process. Numerous 'stem-cell' like cells were found in the blastemal area. The gene regulatory network that specified the different regions of the gut were investigated using ParaHox genes and the echinoderms as biological models. We determined the domains of expression and the function of these genes in sea urchins. We then did the same in starfishes and brittlestars. In these two systems all genes were cloned and in starfish we performed in situ experiments for some ParaHox. The ecdysozoan projects included analysis of the cell lineage and the cell fate of cirripede crustaceans in comparison to that of spiralians. The early cleavage of cirripede crustaceans did not show similarities to spiral cleavage. In contrast, some aspects were shared between arthropod development and that of cycloneuralians such as nematodes and priapulans. This supported the ecdysozoa at the morphological level. The second project compared larval development of two groups of malacostracan crustaceans, namely euphausiacea and dendrobranchiate decapoda, the only two malacostracan groups that passed through a nauplius larva. The fine structures of the nauplius were analysed in comparison to those of larvae of non-malacostracans and malacostracan with direct development. A mitogenomic project included the genomes of a priapulid species but later the focus was set on decapods crustaceans. Mitochondrial genomes of almost 10 species were analysed. The results were in agreement with previous morphological studies and other phylogenies based on nuclear genes. The Ulm projects included an SEM study of fossil Cambrian arthropods as well as an immunohistochemical study of embryonic developmental processes in the brain of the marble crayfish. Single neuronal cells were identified and discussed in a phylogenetic perspective. In addition, an SEM study of 70 specimens of fossil tongue worms was performed. For the first time, details of the ontogeny of fossil tongue worms were revealed. A contribution to the ongoing discussion of the systematic position of tongue worms was added. The Vienna projects focussed on the characterisation and expression of Hox and ParaHox genes in the gastropd gibbula and in tardigrades. Molecular phylogenetics on Mediterranean gibbula species elucidated the complex systematics and nomenclature of this group. The research on tardigrada, i.e. water bears, yielded the sequence of the segmentation genes engrailed and even-skipped, however expression analyses failed due to the inpenetratable cuticle of these animals.

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