Embryo Tolerance and Maternal Control of the Marsupial Environment inArmadillidium vulgare(Isopoda: Oniscidea)

Abstract

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 vulgare cultured in vitro. Marsupial stages were classified as stage 1 (chorionated eggs), stage 2 (having shed the chorion), and stage 3 (mancas). All stages showed wide but differing tolerance ranges. Stage 1 eggs possess the greatest ammonia tolerance, with high 7-d survival in 150 mM total ammonia, and a wide pH tolerance range. Mancas show the widest osmotic tolerance (100-1,400 mosm x kg(-1)) and display proficient hemolymph osmoregulation over this range. Stage 2 eggs reveal the narrowest tolerance ranges for all three parameters but still qualify as eurytopic. Silver staining revealed two distinct ion-transporting tissues in the developmental stages: a median band 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 pleopodal endopodites in mancas. Gravid females do not downregulate ammonia but show efficient regulation of marsupial fluid pH and downregulation of osmolality during dehydration, both of which will provide additional protection to the marsupial young.