Ontogeny of osmoregulation in the brackishwater amphipod Gammarus chevreuxi

Osmoregulation is a key regulatory function in animals inhabiting brackish waters or areas subject to considerable salinity change, such as estuaries. While our understanding of osmoregulation in adult crustaceans is relatively good, our knowledge of how osmoregulatory ability develops during ontogeny is not well documented. In indirect developers, improvement in osmoregulatory capacity during ontogeny appears to coincide with a major metamorphosis. This is consistent with the ‘incomplete adult hypothesis’, which assumes that early developmental stages are ‘incomplete individuals’ operating less efficiently than individuals at the older stages. Evidence for this is not clear in direct developers. Consequently, we tested the ‘incomplete adult hypothesis’, by characterising the ontogeny of osmoregulation of the euryhaline amphipod, Gammarus chevreuxi, a species which undergoes direct development. We investigated the structure and function of putative osmoregulatory tissues, together with the regulation of key osmoregulatory genes. Embryos were examined at key developmental stages: before the dorsal organ (DO), a putative osmoregulatory structure, appeared (