Embryo tolerance and maternal control of the marsupial environment in Armadillidium vulgare (Isopoda : Oniscidea)

Marsupial development in terrestrial isopods subjects embryos to potential physiological stresses, including desiccation, osmotic variation, and high ammonia concentrations. In this study, we investigated tolerance of osmotic extremes, total ammonia, and pH in developmental stages of Armadillidium v ulgare cultured in vitro. Marsupial stages were classified as stage 1 (chor ionated eggs), stage 2 (having shed the chorion), and stage 3 (mancas). All stages showed wide but differing tolerance ranges. Stage 1 eggs possess th e greatest ammonia tolerance, with high 7-d survival in 150 mM total ammoni a, and a wide pH tolerance range. Mancas show the widest osmotic tolerance (100-1,400 mosm kg(-1)) and display proficient hemolymph osmoregulation ove r this range. Stage 2 eggs reveal the narrowest tolerance ranges for all th ree parameters but still qualify as eurytopic. Silver staining revealed two distinct ion-transporting tissues in the developmental stages: a median ba nd on the vitelline membrane of stage 1 and stage 2 eggs, corresponding in location to the embryonic dorsal organ, and the posterior three pairs of pl eopodal endopodites in mancas. Gravid females do not downregulate ammonia b ut show efficient regulation of marsupial fluid pH and downregulation of os molality during dehydration, both of which will provide additional protecti on to the marsupial young.