The evolution of Panpulmonata (Gastropoda) - comparative (3D-) microanatomy and ultrastructure

• Applicant: Dr. Timea Neusser
• Subject Area: Systematics and Morphology (Zoology)
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513333331

Traditional text book concepts on animal evolution are continuously challenged by novel phylogenetic hypotheses based on various, constantly expanding genomic datasets. Unfortunately, a critical re-examination of morphological character sets and evolutionary implications often does not keep track with the pace of novel molecular-based hypotheses.About a decade ago, a novel clade, the ‘Panpulmonata’, has been established among gastropod mollusks. The Panpulmonata is the species-richest and anatomically most diverse gastropod subclade showing several (parallel) habitat shifts in its evolutionary history. Therefore, it is especially suited as model group to explore habitat transitions from sea to freshwater or land. Although the concept of Panpulmonata is widely accepted in the scientific community and has been recovered in phylogenomic as well as transcriptomic approaches, ancestral character states are largely unknown and synapomorphies for Panpulmonata and major subclades are missing. Major impediments for understanding the evolution of Panpulmonata and the morphological adaptations to the frequent habitat shifts within panpulmonate subclades are the doubtful interpretation of scarce and fragmented existing morphological data and the general lack of detailed, reliable and comparable micro-anatomical and ultrastructural data sets. Original panpulmonate species descriptions were often limited to shell and radula morphology or based usually on gross-morphological dissections. Tiny features of e.g. the central nervous system were examined by histological sections indeed, but only in a few selective species. It is overdue to revisit putative opisthobranch and pulmonate morphology, homology, and phenotype evolution. The proposed project will thus generate reliable and detailed comparative morphological and ultrastructural datasets across major panpulmonate taxa from different habitats (marine, limnic, terrestrial). It will combine traditional histology via serial semi-thin sectioning and modern microanatomy using comparable and efficient cutting-edge imaging techniques such as 3D-electron microscopy, X-ray microtomography and serial block-face imaging to fill gaps of microanatomical knowledge in hardly known groups, organs and tissues, and to re-examine, correct and expand existing descriptions. Based on the detailed data, traditionally hypothesized pulmonate and opisthobranch apomorphies will be assessed, previous homology assumptions reconsidered, and the phylogenetic significance of morphological characters evaluated in the light of molecular panpulmonate topologies. Finally, the evolution of organ systems, sperm ultrastructure, ecology and behavior will be reconstructed, leading towards a new understanding of the evolution of Panpulmonata and their frequent habitat shifts.

• DFG Programme: Research Grants