Water-proofing properties of cuticular lipids

SYNOPSIS. Epicuticular lipids play a critical role in allowing arthropods to thrive in terrestrial environments, by reducing transpiration of water through the cuticle. These lipids consist of a diverse array of compounds, especiaUy long-chain hydro-carbons. Rates of water loss are correlated with hydrocarbon structural features, including chain length, unsaturation and methyl-branching. The water-proofing abilities of cuticular lipids appear to depend largely on their physical properties. In most arthropods, rates of water loss increase rapidly above a "transition " tem-perature. A widely accepted model proposes that this transition is due to melting of the surface lipids to a fluid, permeable state. Evidence for this hypothesis has primarily been correlative, due to experimental limitations. Recent technical ad-vances in lipid biophysics and water loss measurements have made it possible to test the lipid melting model more directly. Experiments using model cuticles, in vitro preparations and intact arthropods support the idea that the phase behavior of cuticular lipids is a major factor determining cuticular permeability