Integumental amino acid uptake in a carnivorous predator mollusc (Sepia officinalis, Cephalopoda)

Waterborne amino acids: uptake and functional roles in aquatic animals

Dissolved organic matter is a ubiquitous component of freshwater and marine environments, and includes small nutrient molecules, such as amino acids, which may be available for uptake by aquatic biota. Epithelial transporters, including cotransporters, uniporters and antiporters, facilitate the absorption of dissolved amino acids (often against concentration gradients). Although there is a lack of mechanistic and molecular characterization of such transporters, pathways for the direct uptake of amino acids from the water appear to exist in a wide range of marine phyla, including Porifera, Cnidaria, Platyhelminthes, Brachiopoda, Mollusca, Nemertea, Annelida, Echinodermata, Arthropoda and Chordata. In these animals, absorbed amino acids have several putative roles, including osmoregulation, hypoxia tolerance, shell formation and metabolism. Therefore, amino acids dissolved in the water may play an important, but overlooked, role in aquatic animal nutrition.

Composition and metabolism of phospholipids in Octopus vulgaris and Sepia officinalis hatchlings

The objective of the present study was to characterise the fatty acid (FA) profiles of the major phospholipids, of Octopus vulgaris and Sepia officinalis hatchlings, namely phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylethanolamine (PE); and to evaluate the capability of both cephalopod species on dietary phospholipid remodelling. Thus, O. vulgaris and S. officinalis hatchlings were in vivo incubated with 0.3μM of L-∝-1-palmitoyl-2-[1-(14)C]arachidonyl-PC or L-∝-1-palmitoyl-2-[1-(14)C]arachidonyl-PE. Octopus and cuttlefish hatchlings phospholipids showed a characteristic FA profiles with PC presenting high contents of 16:0 and 22:6n-3 (DHA); PS having high 18:0, DHA and 20:5n-3 (EPA); PI a high content of saturated FA; and PE showing high contents of DHA and EPA. Interestingly, the highest content of 20:4n-6 (ARA) was found in PE rather than PI. Irrespective of the phospholipid in which [1-(14)C]ARA was initially bound (either PC or PE), the esterification pattern of [1-(14)C]ARA in octopus lipids was similar to that found in their tissues with high esterification of this FA into PE. In contrast, in cuttlefish hatchlings [1-(14)C]ARA was mainly recovered in the same phospholipid that was provided. These results showed a characteristic FA profiles in the major phospholipids of the two species, as well as a contrasting capability to remodel dietary phospholipids, which may suggest a difference in phospholipase activities.

Inorganic carbon fixation by chemosynthetic ectosymbionts and nutritional transfers to the hydrothermal vent host-shrimp Rimicaris exoculata

The shrimp Rimicaris exoculata dominates several hydrothermal vent ecosystems of the Mid-Atlantic Ridge and is thought to be a primary consumer harbouring a chemoautotrophic bacterial community in its gill chamber. The aim of the present study was to test current hypotheses concerning the epibiont's chemoautotrophy, and the mutualistic character of this association. In-vivo experiments were carried out in a pressurised aquarium with isotope-labelled inorganic carbon (NaH(13)CO(3) and NaH(14)CO(3)) in the presence of two different electron donors (Na(2)S(2)O(3) and Fe(2+)) and with radiolabelled organic compounds ((14)C-acetate and (3)H-lysine) chosen as potential bacterial substrates and/or metabolic by-products in experiments mimicking transfer of small biomolecules from epibionts to host. The bacterial epibionts were found to assimilate inorganic carbon by chemoautotrophy, but many of them (thick filaments of epsilonproteobacteria) appeared versatile and able to switch between electron donors, including organic compounds (heterotrophic acetate and lysine uptake). At least some of them (thin filamentous gammaproteobacteria) also seem capable of internal energy storage that could supply chemosynthetic metabolism for hours under conditions of electron donor deprivation. As direct nutritional transfer from bacteria to host was detected, the association appears as true mutualism. Import of soluble bacterial products occurs by permeation across the gill chamber integument, rather than via the digestive tract. This first demonstration of such capabilities in a decapod crustacean supports the previously discarded hypothesis of transtegumental absorption of dissolved organic matter or carbon as a common nutritional pathway.

Biology of early life stages in cephalopod molluscs

Recent literature on embryonic and post-embryonic development, biology and behavioural ecology of juvenile cephalopods is reviewed. Emphasis is placed on biological processes. Life-history patterns and phylogenetic systematics, which are important for a proper understanding of the evolutionary history of the cephalopods, are only briefly touched upon. Egg sizes in cephalopods range from less than 1 mm to about 30 mm in diameter, so the hatchlings emerging from the largest eggs are bigger than the adults of pygmy squid, the smallest known cephalopods. Developmental durations from spawning to hatching range from a few days (for very small eggs developing at high temperatures) to one or possibly several years (for very large eggs developing at low temperatures). Such important differences notwithstanding, the morphogenetic processes are very similar in all cephalopod embryos, the major variant being the size of the so-called outer yolk sac, which may be rudimentary in extremely small embryos. Several questions concerning the timing of hatching in relation to the developmental stage attained, especially in terms of yok absorption, need clarification. These questions concern the elimination of the transient closure of the mouth, the final differentiation of digestive gland cells, and the removal of the tranquilliser effect of the perivitelline fluid necessary for the onset of the hatching behaviour. Cephalopod hatchlings are active predators. They refine their behavioural repertoires by learning from individual experience in dealing with prey and would-be predators. There is no truly larval phase, and the ecologically defined term paralarva should be used with caution. Given the considerable resource potential of cephalopods, investigations into dispersal and recruitment are of particular interest to fishery biology, but they are also important for ecological biogeography. The related studies of feeding and growth involve field sampling and tentative age determination of caught specimens, in combination with laboratory studies to test food quality, measure feeding rates, and validation of periodicities in accretional growth structures (e.g. "daily rings" in statoliths).