Cricket Cuticle Water Relations: Permeability and Passive Determinants of Cuticular Water Content

Publisher Website
Google Scholar
Abstract
The water permeability and water content of the cuticle of the cricket Acheta domesticus were examined using gravimetric techniques as well as in vivo and in vitro methods used in conjunction with the transpiration monitor. At 30 C and <5% RH, water loss rates (WLR) in intact, untreated animals exceeded values for live (mouthand anus-sealed) and dead crickets. Individuals immersed in hexane or chloroform: methanol prior to testing exhibited markedly higher WLR. The permeability of thorax cuticle (untreated) measured electronically with a ventilated capsule (in vivo) was slightly greater than the mean value estimated from gravimetric measurements on dead crickets (.027 vs. .017 mg cm⁻² h⁻¹ mmHg⁻¹, respectively); however, in vitro values determined on isolated segments of thoracic cuticle were approximately four times higher. The permeability of hexane-treated cuticle was also significantly higher than that of untreated cuticle, both in the in vivo and in the in vitro procedures. Cuticular water content of crickets kept in dry air was significantly lower than values for crickets held in Ringer-equilibrated air, but there were no significant differences between these measurements made in vivo and in vitro. All of the cuticular water appeared to be held in the endocuticle. The permeabilities of the endocuticle and combined epi-and exocuticles confirm the previously held view that the principal integumental barrier to water is at or close to the surface of the cuticle, with lipids being a primary contributor to this barrier. We conclude that the epidermis plays no significant part in regulating integumental water loss in this species. A simple, passive, two-layer model that is based on equilibrated water contents predicted values for the water content of cuticle having Ringer solution on the inside and dry air outside that are in reasonable agreement with those observed.