Temperature and food influence shell growth and mantle gene expression of shell matrix proteins in the pearl oyster Pinctada margaritifera.

In this study, we analyzed the combined effect of microalgal concentration and temperature on the shell growth of the bivalve Pinctada margaritifera and the molecular mechanisms underlying this biomineralization process. Shell growth was measured after two months of rearing in experimental conditions, using calcein staining of the calcified structures. Molecular mechanisms were studied though the expression of 11 genes encoding proteins implicated in the biomineralization process, which was assessed in the mantle. We showed that shell growth is influenced by both microalgal concentration and temperature, and that these environmental factors also regulate the expression of most of the genes studied. Gene expression measurement of shell matrix protein thereby appears to be an appropriate indicator for the evaluation of the biomineralization activity in the pearl oyster P. margaritifera under varying environmental conditions. This study provides valuable information on the molecular mechanisms of mollusk shell growth and its environmental control.

Fatty acid mobilization and comparison to milk fatty acid content in northern elephant seals.

A fundamental feature of the life history of true seals, bears and baleen whales is lactation while fasting. This study examined the mobilization of fatty acids from blubber and their subsequent partitioning into maternal metabolism and milk production in northern elephant seals (Mirounga angustirostris). The fatty acid composition of blubber and milk was measured in both early and late lactation. Proportions of fatty acids in milk and blubber were found to display a high degree of similarity both early and late in lactation. Seals mobilized an enormous amount of lipid (~66 kg in 17 days), but thermoregulatory fatty acids, those that remain fluid at low temperatures, were relatively conserved in the outer blubber layer. Despite the stratification, the pattern of mobilization of specific fatty acids conforms to biochemical predictions. Long chain (>20C) monounsaturated fatty acids (MUFAs) were the least mobilized from blubber and the only class of fatty acids that showed a proportional increase in milk in late lactation. Polyunsaturated fatty acids (PUFAs) and saturated fatty acids (SFAs) were more mobilized from the blubber, but neither proportion increased in milk at late lactation. These data suggest that of the long chain MUFA mobilized, the majority is directed to milk synthesis. The mother may preferentially use PUFA and SFA for her own metabolism, decreasing the availability for deposition into milk. The potential impacts of milk fatty acid delivery on pup diving development and thermoregulation are exciting avenues for exploration.