Cuticle hydrocarbons show plastic variation under desiccation in saline aquatic beetles

Abstract

In the context of aridification in Mediterranean regions, desiccation resistance and phys-iological plasticity will be key traits for the persistence of aquatic insects exposed to increasingdesiccation stress. Control of cuticular transpiration through changes in the quantity and composi-tion of epicuticular hydrocarbons (CHCs) is one of the main mechanisms of desiccation resistancein insects, but it remains largely unexplored in aquatic ones. We studied acclimation responses todesiccation in adults of two endemic water beetles from distant lineages living in Mediterraneanintermittent saline streams:Enochrus jesusarribasi(Hydrophilidae) andNebrioporus baeticus(Dytisci-dae). Cuticular water loss and CHC composition were measured in specimens exposed to a priornon-lethal desiccation stress, allowed to recover and exposed to a subsequent desiccation treatment.E. jesusarribasishowed a beneficial acclimation response to desiccation: pre-desiccated individualsreduced cuticular water loss rate in a subsequent exposure by increasing the relative abundanceof cuticular methyl-branched compounds, longer chain alkanes and branched alkanes. In contrast,N. baeticuslacked acclimation capacity for controlling water loss and therefore may have a lowerphysiological capacity to cope with increasing aridity. These results are relevant to understandingbiochemical adaptations to drought stress in inland waters in an evolutionary and ecological context.