Distribution of selenium in marine animals: relationship to diet

The chemical form of selenium in the muscle tissues of marine animals in relation to diet has been examined. Inorganic selenium concentrations in all muscle tissues were below the detection limits of the analytical method employed (0.001 mg/kg). Selenium was found to be associated in all tissues predominantly with insoluble proteins. Lipid-soluble and ethanol-soluble selenium constituted less than 18% of the selenium present in tissues and was independent of diet.     

Distribution of arsenic in marine animals: relationship to diet

The chemical form of arsenic in the muscle tissues of marine animals in relation to diet has been examined. Inorganic arsenic concentrations in all muscle tissues were found to be low compared to total arsenic concentrations and independent of diet. Arsenic was found to be present in all tissues predominantly as a methanol-water soluble form. The ratio of lipid soluble and unextractable arsenic to total arsenic was higher in plankton feeders than in herbivores and carnivores.     

Effect of alanine supply on hepatic protein synthesis in animals maintained on a protein free diet

In contrast to what it is observed during starvation, animals maintained on a protein-free isocaloric diet showed an increase in the rate of hepatic peptide chain elongation as determined by measuring the ribosomal transit time in vivo. The loss of body nitrogen per se is insufficient to generate the signal(s) which arrests hepatic peptide chain elongation. This observation suggests that it is an increase in gluconeogenic demand, and not the negative nitrogen balance, which is implicated in determining reciprocal changes in the rate of protein synthesis.The rate of protein synthesis, as expressed per mg of DNA, does not change in protein deprived animals, while the RNA to DNA ratio decreased. These data also agree with a higher ribosomal efficiency at the elongation step. The animals maintained on a protein-free diet have a decreased hepatic content of protein and an increased concentration of valine, indicating an increased proteolysis.The enhanced rate of polypeptide elongation observed in animals kept on a protein-free diet was accompanied by decreases in the state of aggregation of polyribosomes and in the ability of liver extracts to form eIF-2 catalyzed ternary complexes. These observations suggest that the activity of the hepatic initiation factor in vivo may not be rate limiting.The administration of alanine in vivo to animals maintained on a protein-free diet showed a preferential effect in reaggregating polyribosomes. This action was neither accompanied by detectable effects on the rate of eIF-2 catalyzed ternary complexes formation nor by significant changes in the rate of elongation. It is concluded that factors other than eIF-2 activity or the rate of polypeptide elongation must be controlling the hepatic polyribosomal state of aggregation.     

The importance of seahorses and pipefishes in the diet of marine animals

A review of 135 accounts of predation on seahorses and pipefishes identified 82 predator species, with nine species of seahorses and 25 of pipefishes recorded as prey. These cryptic fishes were generally depredated in low numbers. Where syngnathids formed a high proportion of predator diets, predation occurred on (1) a single abundant species during a population boom or large die-off, (2) concentrations of individuals utilising floating marine vegetation, or (3) juveniles when abundant during the breeding season. Predation coinciding with high syngnathid densities suggests their predators are foraging opportunistically rather than targeting syngnathids as prey. Invertebrates, fishes, sea turtles, waterbirds and marine mammals were all syngnathid predators: these included taxa that do not frequent the demersal habitat generally occupied by seahorses and pipefishes. Thus, seahorses and pipefishes may be moving in the open ocean more than suspected, perhaps using floating mats of marine vegetation. If so, this behaviour could act as a hitherto unknown vector for syngnathid movement and dispersal. Information on syngnathid abundance in predator diet (measured as percent number, volume, or mass) was available in 45 reviewed accounts; in 27% (n = 12) of these studies seahorses or pipefishes comprised ≥20% of predator diet (range 0.005–100%). Frequency of occurrence (percent stomachs, seabird bill-loads, or regurgitations in which a prey item occurred) was provided in 39 accounts, with 15% (n = 6) of these recording a frequency of ≥20% (range 0.003–65%).     

Hepatic and intestinal formation of polar sterols in vivo in animals fed on a cholesterol-supplemented diet.

Measurements were made of the activities of the enzymes of the 'de novo' and salvage pathways of purine synthesis [phosphoribosyl pyrophosphate amidotransferase (EC 2.4.2.14), adenine phosphoribosyltransferase (EC 2.4.2.7) and hypoxanthine phosphoribosyltranferase (EC 2.4.2.8)] at different stages of the lactation cycle, and the effects of diabetes on the activity of these enzymes in lactation were studied. A distinctive pattern of enzyme change was observed, in which the 'de novo' pathway enzyme phosphoribosyl pyrophosphate amidotransferase increased sharply between days 10 and 14 of pregnancy, and then remained sensibly constant until the height of lactation, whereas the enzymes of the salvage pathway increased later in pregnancy and continued to rise during lactation. Diabetes severely depressed the activity of the enzymes of the salvage pathway, but appeared to be without effect on the 'de novo' pathway enzyme. These results are discussed in relation to the provision of purine precursors from tissues outside the mammary gland.     

Variation between individuals and the consequences for diet selection by groups of animals

We describe a model to predict the diet selection of a population of animals, based on simple assumptions about the characteristics of the individuals in a population, including the variation between them. Individuals are characterized by three parameters with biological relevance; a nutrient (protein) requirement, an ability to discriminate between foods of different protein contents and a need to collect information about both foods. Each animal selects perfectly a diet that avoids both a deficiency and an excess of protein, where this is possible. To construct the population two further assumptions are made. The first is that the values of each parameter are drawn from uncorrelated normal distributions subject to the values being logically possible. The second is that, for different mean values for the population, the standard deviation is directly proportional to the mean so that the coefficient of variation is independent of the mean. The model was used to predict the outcomes of six hypothetical experiments, using 100 individuals on each treatment, where the values of the three parameters were systematically varied. In the experiments one food was always of low protein content while the protein content of the other was the treatment variable. The quantitative effects of varying either the mean value of the parameters, or their variation, on both the mean composition of the diet selected, and on its variation, were not possible to predict without using the model. The shape of the population response was different to that for any individual. Extensions to the model may be able to increase its relevance to practical issues of diet selection. Copyright 2000 The Association for the Study of Animal Behaviour.