Evolutionary transition to freshwater by ancestral marine palaemonids: evidence from osmoregulation in a tide pool shrimp

The transition from marine/brackish waters to freshwater habitats constitutes a severe osmotic and ionic challenge, and successful invasion has demanded the selection of morphological, physiological, biochemical and behavioral adaptations. We evaluated short-term (1 to 12 h exposure) and long-term (5 d acclimation), anisosmotic extracellular (osmolality, [Na(+), Cl(-)]) and long-term isosmotic intracellular osmoregulatory capability in Palaemon northropi, a neotropical intertidal shrimp. F northropi survives well and osmo- and ionoregulates strongly during short- and long-term exposure to 5-45 parts per thousand salinity, consistent with its rocky tide pool habitat subject to cyclic salinity fluctuations, Muscle total free amino acid (FAA) concentrations decreased by 63% in shrimp acclimated to 5%. salinity, revealing a role in hypoosmotic cell volume regulation; this decrease is mainly a consequence of diminished glycine, arginine and proline. Total FAA contributed 31% to muscle intracellular osmolality at 20 parts per thousand, an isosmotic salinity, and decreased to 13% after acclimation to 5 parts per thousand. Gill and nerve tissue FAA concentrations remained unaltered. These tissue-specific responses reflect efficient anisosmotic and anisoionic extracellular regulatory mechanisms, and reveal the dependence of muscle tissue on intracellular osmotic effectors. FAA concentration is higher in P. northropi than in diadromous and hololimnetic palaemonids, confirming muscle FAA concentration as a good parameter to evaluate the degree of adaptation to dilute media. The osmoregulatory capability of P. northropi may reflect the potential physiological capacity of ancestral marine palaemonids to penetrate into dilute media, and reveals the importance of evaluating osmoregulatory processes in endeavors to comprehend the invasion of dilute media by ancestral marine crustaceans.

Infestation rates of the pedunculated barnacle Octolasmis lowei (Cirripedia: Poecilasmatidae) on the spider crab Libinia spinosa (Decapoda: Majoidea)

The prevalence and infestation intensities of Octolasmis lowei in the bronchial chambers of Libinia spinosa were evaluated according to the host's sex, size, and moult condition. Epibionts were classified as cyprid larvae, non-ovigerous or ovigerous according to their developmental stage. A median intensity of infestation of 21 epibionts/host was found (range = 1-644; Q(3) = 81). Epibiont prevalence values (88%) were higher on ovigerous female hosts than on males (55%) or on non-ovigerous females (31%). Intensity of infestation was positively correlated with host size in both sexes for non-ovigerous and ovigerous epibionts. No preference between host sex by cyprid larvae was observed, nor any correlation between cyprid abundance and host size. Cyprid larvae abundance was positively correlated with settled epibionts on both host sexes. The duration of the intermoult phase was the main factor linked to the establishment of sessile epibionts. These observations are important in relation to crabs that have a terminal moult, because these animals cannot eliminate their epibionts in future moults, thus increasing the importance of density-dependent mechanisms on epibiont establishment; in that way, prevalence of infestation alone can underestimate the real impact of infestation on the host's life cycle.

Diversity of decapod crustaceans at the interface of unconsolidated seabed areas and rocky shores in tropical/subtropical Brazil

The decapod crustacean assemblages from unconsolidated seabed areas located near rocky shores in the Ubatuba region on the south-east coast of Brazil were analysed by investigating the abundance, richness, diversity and dominance of species. The relationships of the sediment and bottom-water temperature to total species abundance, richness and diversity were also evaluated. Monthly samples were taken from January 1998 through December 1999 at sites in Ubatumirim and Mar Virado. At each locality, three areas were defined as either 'exposed', 'sheltered' or 'island'. The highest species abundance was found in the sheltered area of Ubatumirim and the exposed area of Mar Virado, and during autumn. At Ubatumirim, the highest richness occurred in the exposed area and the highest diversity near the island. At Mar Virado, the highest richness and diversity were found near the island. Autumn and winter collections yielded the highest richness but the lowest diversity. The higher diversities, which were measured near the islands and during spring and summer, were consequences of the greater evenness of the data. The areas with the highest diversity also had the most heterogeneous sediment composition, thus reinforcing the hypothesis that areas with more complex substrata support more diverse faunas.