Comparative neuroanatomy and evolution of visual systems in Chelicerata… towards a comparative analysis of neuron networks

• Applicant: Dr. Tobias Lehmann
• Subject Area: Systematics and Morphology (Zoology)
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 290127846

The visual systems in chelicerates are poorly understood, even though they show strong variation in eye and optic lobe architecture, and may provide valuable insights for the understanding of arthropod phylogeny and eye evolution. Moreover, comparable morphological characters are desperately needed to reconstruct the phylogeny of Chelicerata. This task ranks among the major challenges in arthropod systematics, especially since morphological and molecular studies have repeatedly produced incongruent trees. According to the concepts of neurophylogeny and neural cladistics, characters of the nervous system can provide powerful evidence about phylogeny.Therefore, I seek to undertake a comparative analysis of the neuroanatomy of visual systems in Chelicerata. So far, reliable information exists only for Xiphosura (Limulus), Araneae (one relatively derived species), Scorpiones, and Pycnogonida - the latter two data sets from my dissertation project and publications in high ranked journals. In the present project I will apply the full spectrum of available neuroanatomical techniques (immunohistochemistry, cobalt fills, DiI/DiO labelling, Golgi impregnations, Wigglesworth technique, classical histology, TEM, micro-CT, and AMIRA) to representatives of hitherto unstudied chelicerate taxa (Araneae, Amblypygi, Uropygi, Pseudoscorpiones, and Solifugae).The results are expected to provide the first comprehensive and robust set of characters of the chelicerate visual systems, and to allow confident reconstruction of phylogeny in the second most diverse main lineage in Arthropoda. By integrating the new morphological data with existing molecular evidence I will evaluate (1) the validity of Tetrapulmonata as the only stable monophylum in Arachnida, (2) the unsolved sister group relationship of Scorpiones, and (3) the potential monophyly of Arachnida and several of its subordinate groups. In addition, (4) a re-evaluation of homology assumptions could be the key to understanding whether the standard textbook separation of median and lateral arthropod eyes reflects evolution correctly or is unfounded.

• DFG Programme: Research Grants