Neuronal Regression of Internal Leg Vibroreceptor Organs in a Cave-Dwelling Insect (Orthoptera: Rhaphidophoridae: Dolichopoda araneiformis)

作者：Strauss Johannes; Stritih Natasa

来源：Brain, Behavior and Evolution, 2017, 89(2): 104-116.

DOI：10.1159/000462957

• Insect
• Neuroanatomy
• Cave cricket
• Chordotonal organ
• Mechanoreceptor
• Sensory evolution
• Neuronal innervation
• Troglomorphism
• Troglobite

Animals' adaptations to cave habitats generally include elaboration of extraoptic senses, and in insects the receptor structures located on the legs are supposed to become more prominent in response to constant darkness. The receptors for detecting substrate vibrations are often highly sensitive scolopidial sensilla localized within the legs or the body. For troglobitic insects the evolutionary changes in vibroreceptor organs have not been studied. Since rock is an extremely unfavorable medium for vibration transmission, selection on vibration receptors may be weakened in caves, and these sensory organs may undergo regressive evolution. We investigated the anatomy of the most elaborate internal vibration detection system in orthopteroid insects, the scolopidial subgenual organ complex in the cave cricket Dolichopoda araneiformis (Orthoptera: Ensifera: Rhaphidophoridae). This is a suitable model species which shows high levels of adaptation to cave life in terms of both phenotypic and life cycle characteristics. We compared our data with data on the anatomy and physiology of the subgenual organ complex from the related troglophilic species Troglophilus neglectus. In D. araneiformis, the subgenual organ complex contains three scolopidial organs: the subgenual organ, the intermediate organ, and the accessory organ. The presence of individual organs and their innervation pattern are identical to those found in T. neglectus, while the subgenual organ and the accessory organ of D. araneiformis contain about 50% fewer scolopidial sensilla than in T. neglectus. This suggests neuronal regression of these organs in D. araneiformis, which may reflect a relaxed selection pressure for vibration detection in caves. At the same time, a high level of overall neuroanatomical conservation of the intermediate organ in this species suggests persistence of the selection pressure maintaining this particular organ. While regressive evolution of chordotonal organs has been documented for insect auditory organs, this study shows for the first time that internal vibroreceptors can also be affected.

• 出版日期2017