Decapod egg membranes: powerful barriers or regulatory structures?

Abstract

Osmoregulatory abilities and mechanisms of adults and larvae of decapod crustaceans have been extensivelyinvestigated. However, how embryos carried by their mothers can deal with changing or extreme salinitiesis less understood. The egg membranes are believed toisolate embryos from a challenging environment, although osmoregulatory ability has been demonstratedin early developing embryos (naupliar stage) of two crabs. To establish whether embryos areisolated by their membranes and/or are able to osmoregulate, we measured the survival and volume change over 48 h of oocytes and embryosin different stages of three carideans (Betaeus lilianae, Palaemon macrodactylus and P. argentinus) and the brachyuran Neohelice granulata, subjected to different salinities.in addition, we recorded osmolality changesin homogenates of the same stagesin P. argentinus and N. granulata after 2 h of exposure and mapped the presence of putative sites ofions exchangein the membrane of all species. High mortality, whenit occurred, was associated with low salinity and mortality variation with the stage of development depended on the species. All species precipitated silver saltsin or under the egg envelope, with a different pattern between carideans and the brachyuran. Changesin osmolality and egg volume after hypo- or hyper-osmotic salinity challengesindicate that eggs are not fullyisolated by their membranes, and that some osmoregulatory mechanisms arein play to maintain developmental homeostasis.We suggest that egg membranes can participatein osmoregulation by selectively transportingions to anintramembrane space, with differences between carideans and brachyurans.