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Salinity is an abiotic factor that may impact survival and fitness of terrestrial insects in coastal environments. Meanwhile, some terrestrial arthropods can survive in hypersaline environments, and counterbalance osmotic stress by intra- and extracellular buildups of organic osmolytes. The ground beetle Merizodus soledadinus originates from South America and it is distributed in forests and riparian zones, where salinity levels are considerably low. This species has been introduced at the Kerguelen Islands a century ago, where it colonized coastal areas (tide drift lines), and must thus withstand salinity variations due to tide, spray, and organic matter deposited therein. In the present study, we addressed the physiological plasticity of M. soledadinus to saline conditions, by monitoring body water content and survival in adults experimentally subjected to different salinities. We also investigated possible metabolic adjustments involved at three contrasted salinity levels (0 parts per thousand, 35 parts per thousand, 70 parts per thousand) at 4 and 8 degrees C. We hypothesized that this invasive ground beetle can withstand a broad range of salinity conditions thanks to the plastic accumulation of compatible solutes. The study revealed a progressive drop in body water content in individuals exposed to 35 parts per thousand and 70 parts per thousand, as opposed to the controls. Metabolic fingerprints showed compatible solute (erythritol, alanine, glycine and proline) accumulation at medium and high salinity conditions (35 parts per thousand and 70 parts per thousand). We concluded that the osmo-induced accumulation of amino acids and polyols was likely to modulate the ground beetles’ body water balance on medium saline substrates, thus enhancing their survival ability. (C) 2012 Elsevier Ltd. All rights reserved.