Osmoregulation in littoral and terrestrial talitroidean amphipods (Crustacea) from Britain

Abstract

Osmoregulation was investigated in both aerated seawater and on saturated sand in four species of talitrid amphipods, Talitrus saltator (Montagu), Orchestia gammarellus (Pallas), Orchestia cavimana (Heller) and Arcitalitrus dorrieni (Hunt). The Osmoregulation of one species of intertidal hyalid amphipod Hyale nilssoni (Rathke) was also investigated. Appreciable differences were demonstrated in the osmoregulatory abilities of the species. Whilst the marine supralittoral species O. gammarellus and T. saltator demonstrated the ability to hypo-regulate at higher external concentrations ( > 800 mOsm), they hyper-regulated at lower concentrations, maintaining the haemolymph concentration between 750–850 mOsm. The fresh-water and estuarine supralittoral species O. cavimana and the landhopper A. dorrieni did not have this capacity; both these species maintained the haemolymph hyper-osmotic between external concentrations of 50–900 mOsm. The intertidal H. nilssoni also demonstrated this hyper-osmotic regulation pattern. Hyper-regulation in O. cavimana between external concentrations of 15–290 mOsm was at least partially mediated by the production of hypo-osmotic urine from the antennary gland. The landhopper A. dorrieni produced isosmotic urine as did the hyper-hypo regulating O. gammarellus. There was, however, some evidence that hyper-regulating T. saltator may also produce hypo-osmotic urine. Survivals under different acclimation regimes largely reflect the original habitat of the species: the estuarine/marine supralittoral species were tolerant of a wide range of salinities in water and on sand: the freshwater species showed reduced survival at higher salinities (1200 mOsm) but higher survival than its marine relations in freshwater (<20 mOsm). The landhopper was tolerant of a wide range of salinities but survivals at low (<50 mOsm) and high ( > 900 mOsm) salinities were greater on sand than in water. The results are discussed in relation to the habitats of the species and in relation to the presumed evolutionary history of the group as a whole.