Mechanosensory analysis of the scolopidial distal organ in stick insects

• Applicant: Dr. Johannes Strauß
• Subject Area: Sensory and Behavioural Biology ; Cognitive, Systems and Behavioural Neurobiology
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 414216545

• Final Report Year: 2024

Final Report Abstract

This project analyses the subgenual organ complex in stick insects (Phasmatodea) which is located in the proximal tibia of all legs and consists of two mechanosensory chordotonal organs, the subgenual organ and the distal organ. The distal organ shows a highly elaborate organisation with sensory neurons oriented in a linear array in proximaldistal orientation in the tibia. The morphology of the distal organ was analysed for an understanding of the sensory specialisations of two mechanosensory organs placed in close proximity to each other. Different placements or attachments of the respective organs within the tibia were hypothesised to correlate with different mechanical input pathways. The subgenual organ and distal organ were shown to be present in all stick insects groups. Both organs are placed in the hemolymph channel, and dendrites of sensory neurons are oriented in distal direction in the tibia. The distal organ was usually well-developed and contains 20 – 50 sensilla. It was attached at the to the leg cuticle at its proximal part, and by fine strands of tissue at its central and distal part. Notably, the distal organ was not located close to the leg cuticle or prominently attached to it. By the position of the sensory organs, both are likely responding to substrate vibrations transferred by the leg hemolymph. Functional morphology also showed that the two chordotonal organs were linked by a fine membrane medially and a connective tissue strand dorsally. The membrane appeared to extend the subgenual organ in different direction towards the distal organ, which is likely providing a connection that is mechanically relevant for both organs. This membrane was documented in species from different taxa and presumably belongs to the general organisation of the subgenual organ complex in this group. The neuroanatomy of the subgenual organ complex across different taxa of stick insects is very homogenous. One notable difference is the structure of the distal organ in Timematodea, the most basal group of Phasmatodea. In Timema species, the distal organ consisted of very few sensory neurons only, that were oriented linearly, but with gaps between the cell bodies. This represents an evolutionary intermediate form between a group of sensilla in the distal organ in cockroaches, and the packed linear sensilla array in higher stick insects. This intermediate neuroanatomy identifies for the first time the anatomical changes into a linear chordotonal organ in a phylogenetic framework. The functional morphology of the distal organ indicates a vibrosensory function, while the broad taxonomic occurance of the elaborate distal organ emphasises the physiological relevance in Phasmatodea.

Publications

• Early postembryogenic development of the subgenual organ complex in the stick insect Sipyloidea sipylus. Arthropod Structure & Development, 56, 100933.
  Strauß, Johannes
  
• Neuronal Innervation of the Subgenual Organ Complex and the Tibial Campaniform Sensilla in the Stick Insect Midleg. Insects, 11(1), 40.
  Strauß, Johannes
  
• Communication by substrate-borne mechanical waves in insects: From basic to applied biotremology. Advances in Insect Physiology, 189-307. Elsevier.
  Strauß J., Stritih-Peljhan N., Nieri R., Virant-Doberlet M. & Mazzoni V.
  
• The Subgenual Organ Complex in Stick Insects: Functional Morphology and Mechanical Coupling of a Complex Mechanosensory Organ. Frontiers in Ecology and Evolution, 9.
  Strauß, Johannes; Moritz, Leif & Rühr, Peter T.
  
• The tracheal system in the stick insect prothorax and prothoracic legs: Homologies to Orthoptera and relations to mechanosensory functions. Arthropod Structure & Development, 63, 101074.
  Strauß, Johannes
  
• “Neuroanatomy and postembryonic development of the subgenual organ complex in stick insects.” Poster T20-4, 14th NWG Meeting 2021, Göttingen, Germany
  Strauß J., Moritz L. & Rühr P.T.
  
• Comparative Neuroanatomy of the Mechanosensory Subgenual Organ Complex in the Peruvian Stick Insect, Oreophoetes peruana. Brain, Behavior and Evolution, 98(1), 22-31.
  Strauß, Johannes
  
• Morphological coupling of the distal organ in the Peruvian walking stick (Oreophoetes peruana): Structural and functional aspects. Invertebrate Biology, 141(4).
  Strauß, Johannes
  
• Vibration detection in arthropods: Signal transfer, biomechanics and sensory adaptations. Arthropod Structure & Development, 68, 101167.
  Strauß, Johannes & Stritih-Peljhan, Nataša
  
• The neuronal innervation pattern of the subgenual organ complex in Peruphasma schultei (Insecta: Phasmatodea). Arthropod Structure & Development, 74, 101277.
  Strauß, Johannes
  
• “Functional morphology of a leg mechanoreceptor complex in stick insects.“ CMBB Center for Mind, Brain and Behavior, Justus-Liebig-Universität Gießen, 10/ 2023.
  Strauß J., Moritz L. & Rühr P.T.
  
• Vibration receptor organs in the insect leg: neuroanatomical diversity and functional principles. Current Opinion in Insect Science, 61, 101153.
  Strauß, Johannes; Stritih-Peljhan, Nataša & Nishino, Hiroshi