Graduate Thesis Or Dissertation

The pectines of scorpions : analysis of structure and function

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  • This is a neuroanatomical and ethological study of the pectines, the primary chemosensory organs of scorpions (Arachnida: Scorpiones). The pectines are paired, ventromedial appendages that brush the substrate as the scorpion walks. This comb-like organ consists of a supportive spine and an array of teeth. Each tooth supports hundreds of setaform sensilla called pegs. The peripheral neuroanatomy of sensilla on the teeth and spine were described. Below the peg sensilla on the pectinal teeth were three histological layers consisting of dendrites, neuronal somata, and a layer of peripheral synapses. The neuronal cell layer within the teeth was further divided into inner and outer sub-larninae, comprised of chemosensory and mechanosensory neurons. The peg sensilla were innervated by iterative cassettes of sensory neurons orthogonal to the layers described. Sensory hairs on the pectinal spine resembled arachnid tactile and chemosensory hairs. The central projection patterns of sensory afferents from tactile hairs on the pectinal spine and peg sensilla on the pectinal teeth were compared. The internal architecture of the neuropile serving the pectines was also characterized. The pectinal neuropile contained a basal disk and a terminal cap. The cap was divided into a fibrous cortex and a medullar region of glomeruli. Sensory afferents from the tactile hairs on the spine were aligned topographically in the pectinal neuropile, but were restricted to the outer cortex. Sensory afferents from the bimodal peg sensilla terminated in both regions of the pectinal neuropil, suggesting that the cortex and medulla are functionally divided into mechanosensory and chemosensory processing areas. Behavioral experiments were conducted using a Y-maze choice test to determine if male scorpions were capable of trailing female conspecifics. A significant proportion of male scorpions preferred the arm of the Y-maze that a conspecific female had walked down and pre-courtship behaviors were only evoked when male scorpions contacted substrates that had been exposed to a female scorpion. The results from this experiment suggest that scorpions may use chemical cues to find potential mates and to initiate courtship.
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