Low radiodensity μCT scans to reveal detailed morphology of the termite leg and its subgenual organ

Functional Morphology of Leg Mechanosensory Organs in Early Postembryonic Development in the Stick Insect (Sipyloidea chlorotica)

The subgenual organ complex of stick insects has a unique neuroanatomical organisation with two elaborate chordotonal organs, the subgenual organ and the distal organ. These organs are present in all leg pairs and are already developed in newly hatched stick insects. The present study analyses for the first time the morphology of sensory organs in the subgenual organ complex for a membrane connecting the two sensory organs in newly hatched insects (Sipyloidea chlorotica (Audinet-Serville 1838)). The stick insect legs were analysed following hatching by axonal tracing and light microscopy. The subgenual organ complex in first juvenile instars shows the sensory organs and a thin membrane connecting the sensory organs resembling the morphology of adult animals. Rarely was this membrane not detected, where it is assumed as not developed during embryogenesis. The connection appears to influence the shape of the subgenual organ, with one end extending towards the distal organ as under tension. These findings are discussed for the following functional implications: (1) the physiological responses of the subgenual organ complex to mechanical stimuli after hatching, (2) the influence of the membrane on the displacement of the sensory organs, and (3) the connection between the subgenual organ and distal organ as a possible functional coupling.

Vibration receptor organs in the insect leg: neuroanatomical diversity and functional principles

Detecting substrate vibrations is essential for insects in different behavioural contexts. These vibrational behaviours are mediated by mechanoreceptor organs detecting and processing vibrational stimuli transmitted in the environment. We discuss recently gained insights about the functional principles of insect vibration receptors, mainly leg chordotonal organs highly sensitive to vibrational stimuli, and the mechanisms of their diversification in neuroanatomy and functional morphology, in relation to the attachment structures and mechanical coupling. The two main input pathways for vibration stimuli transferred by the insect legs to vibrosensory organs via the cuticle and via the hemolymph are fundamental for explaining sensory specialisations. The vibroreceptor organs can diversify in their neuroanatomy and morphology in several key aspects. This provides the structural basis for complex adaptations in sensory evolution.