WATERPROOFING PROPERTIES OF CUTICULAR LIPIDS

Epicuticular Lipids play a critical role in allowing arthropods to thr ive in terrestrial environments, by reducing transpiration of water th rough the cuticle. These lipids consist of a diverse array of compound s, especially long-chain hydrocarbons. Rates of water loss are correla ted with hydrocarbon structural features, including chain length, unsa turation and methyl-branching. The water-proofing abilities of cuticul ar lipids appear to depend largely on their physical properties. In mo st arthropods, rates of water loss increase rapidly above a ''transiti on'' temperature. A widely accepted model proposes that this transitio n is due to melting of the surface lipids to a fluid, permeable state. Evidence for this hypothesis has primarily been correlative, due to e xperimental limitations. Recent technical advances in lipid biophysics and water loss measurements have made it possible to test the lipid m elting model more directly, Experiments using model cuticles, irt vitr o preparations and intact arthropods support the idea that the phase b ehavior of cuticular lipids is a major factor determining cuticular pe rmeability.