Form and evolution of the hexapod tracheal system

• Applicant: Dr. Benjamin Wipfler
• Subject Area: Systematics and Morphology (Zoology)
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 463181221

The general aim of the present proposal is to derive a conclusive picture of the evolution of the tracheal system among hexapods. Our understanding of this system is largely limited due to the missing data for various groups, the difficulties to study it with traditional methods and the lack of any evolutionary interpretations. We will close these gaps by addressing the following major questions: I) How much intraspecific variation is in the tracheal system of different hexapod representatives? II) Is the tracheal system part of the hexapod ground plan or did it evolve several times independently as implied by the sparse available literature? What were the major evolutionary steps in the hexapod tracheal system and did the system get increasingly complex? III) How is the size and complexity of the tracheal system related to the body size? Do larger / smaller animals have a comparatively larger / smaller tracheal system and does the respiratory system state an upper or lower size boundary for hexapods? We will achieve this by studying various morphological character systems such as position, shape and musculature of the spiracles, the number and presence of anastomoses, the tracheal ultrastructure and the shape and arrangement of taenidia with a broad set of state-of-the-art morphological methods including µ-computed tomography, digitalized histological sections, scanning and transmission electron microscopy and 3-dimensional reconstructions. The retrieved results will be analysed in a sound phylogenetic framework in order to understand the major evolutionary transformations. In a second step, the gathered 3D data will be used as a base for complex morphometric approaches including determinations of fractal dimensions, centrality, network motifs, volumes or branching rates. These approaches will allow to understand the complex 3-dimensional shape of the tracheal system and to correlate it with body size and form of the respective animal. In our preliminary work, we established the workflow and can show that the proposed work programme is feasible and can be accomplished in the given timeframe. The proposed project would greatly improve our understanding of the hexapod respiratory system and its adaptations. It would be the first attempt to I) understand the morphological transitions of the hexapod tracheal system in a phylogenetic context, to II) address the correlation between body size and shape of the tracheal system for miniature species in general and for gigantic species in a 3D approach and to III) quantifiably determine intraspecific variation in this character system.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Jörg Hammel