Ionic requirements of transepithelial potential difference and net water flux in the perfused midgut of the american lobster, Homarus americanus

Ecophysiological adaptation to salinity throughout a life cycle: a review in homarid lobsters

Adaptations to salinity are reviewed throughout development in both species of the genus Homarus. Some populations of homarid lobsters are known to inhabit coastal and estuarine areas where salinity fluctuates. Salinity tolerance varies during development, with 50 % lethal salinities (LS(50)) ranging from approximately 15–17 in larvae to approximately 12 in postlarvae and 10 in adults. Larval and adult lobsters can avoid low-salinity areas using behavioural strategies. When exposed to low salinity, the capacity to osmoregulate varies with development. Embryos are osmoconformers and are osmotically protected by the egg membranes. Larvae are also osmoconformers, and the pattern of osmoregulation changes at metamorphosis to hyper-regulation, which is retained throughout the later stages up to the adult stage. Exposure to low salinity increases the activity of Na(+)/K(+)-ATPase in postlarvae and later stages. The level of osmoregulation evaluated through the osmoregulatory capacity (the difference between haemolymph and medium osmolalities) is negatively affected by low temperature (2 degrees C). The variations in haemolymph osmolality resulting from osmoconforming or partial osmoregulation are compensated by intracellular iso-osmotic regulation. Neuroendocrine control of osmoregulation appears in postlarvae and seems to involve the crustacean hyperglycaemic hormone. In adult lobsters, the gills appear to have a respiratory function only, and extracellular osmoregulation is effected by the epipodites, with the addition of the branchiostegites at low salinity. These organs are present at hatching. Transmission electron microscopy and immunolocalization of Na(+)/K(+)-ATPase reveal that the epipodites become functional in larvae and that the branchiostegites become functional in postlarvae. An integrated series of events links the appearance of osmoregulatory tissues, the increase in Na(+)/K(+)-ATPase activity, the occurrence in postlarvae of hyper-regulation at low salinity and the increase in salinity tolerance. Further ecological and physiological studies are proposed for a better understanding of the adaptive significance of the ontogeny of osmoregulation in lobsters.

Ecdysteroids in relation to the molt cycle of the American lobster, Homarus americanus. II. excretion of metabolites

Ecdysteroid (Ecd) excretion patterns were followed during the molt cycle of adult male and female lobsters. Homarus americanus. Urine was the major route of Ecd elimination, amounting to greater than or equal to 96% of the excreted radioimmunoassay activity for all molt stages. The other identified route of Ecd elimination from the hemolymph was the feces, which accounted for the remaining 4% of the total Ecd excretion. High polarity metabolites (HP), including 20,26-dihydroxyecdysone (2026E) and 20-hydroxyecdysonoic acid (20EA), were the major types of Ecds found in the urine. Other urinary Ecd components included 20-hydroxyecdysone (20E), ecdysone (E), and ponasterone A (P). The major portion of urinary HP was composed of conjugates of 2026E, 20E, E, P, and other unidentified metabolites. The fecal Ecds were predominately HP and apolar metabolites. Apolar fecal Ecds were hydrolyzable to release 20EA, 2026E, 20E, E, P, and other metabolites. By means of intubation, [3H]E was placed directly into the cardiac stomach of lobsters. The gut pathway formed an apolar conjugate of [3H]E which was found exclusively in the feces. Lobsters are therefore capable of excreting ingested Ecds without absorption.

Neuroendocrine control of hydromineral regulation in the American lobster Homarus americanus H. Milne-Edwards 1837 (Crustacea, Decapoda). 1. Juveniles

Juvenile lobsters survive well in salinities above 10.2% (300 mOsm/kg), and their osmotic and ionic (Cl-, Na+, Ca2+) regulation in dilute sea water is slightly hyperosmotic, similar to that of adults. Approximately a month after eyestalk ablation, osmotic and ionic (Cl-, Na+) regulation becomes isosmotic, water content increases, and survival rate in dilute sea water declines, but these changes can be partially reversed by implantation of eyestalk neuroendocrine tissue. Regulation of Ca2+, in contrast, is only slightly affected by eyestalk ablation. These results indicate that osmotic regulation and regulation of hemolymph Na+ and Cl- concentrations are at least partly controlled by eyestalk neuroendocrine factors in this species.