Timing of isotopic integration in marine mammal skull: comparative study between calcified tissues.

RATIONALE: Tissues with different turnover rates have different isotope compositions and reflect the different periods in an animal's life when the isotopes are incorporated during the growth of tissues. Bone is one of the most used tissues for reconstruction of an animal's diet; however, the time of isotope integration remains unknown for many species. METHODS: The δ(15)N and δ(13)C values in tooth dentine and bone tissue from the maxilla and mandible of 21 stranded northern elephant seals, Mirounga angustirostris, collected on the San Benito and Magdalena Islands, Mexico, between 2000 and 2008 were compared. Bone and dentine samples from each growth layer within the tooth were analyzed using a PDZ Europa ANCA-GSL elemental analyzer interfaced with a PDZ Europa 20-20 continuous flow gas source mass spectrometer. RESULTS: The δ(15)N and δ(13)C values were not different between bone structures, indicating similar turnover rates, metabolic activity and amino acid compositions. The differences in the observed δ(13)C values between tissues are probably indicative of differences in their amino acid compositions, although the similarities in δ(15)N values indicated less variation from different amino acids. Correlation of the analyses between isotopic values of tissues suggests that the maxilla and/or mandible of M. angustirostris might reflect the δ(15) N signal incorporated during the last 5 years of life of the individuals. CONCLUSIONS: This study demonstrated the usefulness of the applied approach for providing a best approximation of the timing of isotopic integration into the skull of a marine mammal, thereby reducing uncertainty in exploring historic changes in the species' feeding behavior.

Persistent organic pollutants and stable isotopes in pinnipeds from King George Island, Antarctica.

In the present work, fat, skin, liver and muscle samples from Leptonychotes weddellii (Weddell seal, n=2 individuals), Lobodon carcinophagus (crabeater seal, n=2), Arctocephalus gazella (Antarctic fur seal, n=3) and Mirounga leonina (southern elephant seal, n=1) were collected from King George Island, Antarctica, and analysed for POPs (PCBs, organochlorine pesticides and PBDEs) and stable isotopes (δ¹³C and δ¹5N in all tissues but fat). PBDEs could be found in only one sample (L. weddellii fat). Generally, PCBs (from 74 to 523 ng g⁻¹ lw), DDTs (from 14 to 168 ng g⁻¹ lw) and chlordanes (from 9 to 78 ng g⁻¹ lw) were the prevailing compounds. Results showed a clear stratification in accordance with ecological data. Nonetheless, stable isotope analyses provide a deeper insight into fluctuations due to migrations and nutritional stress. Correlation between δ(15)N and pollutants suggests, to some degree, a considerable ability to metabolize and/or excrete the majority of them.

Lactational transfer of PCBs and chlorinated pesticides in pups of southern elephant seals (Mirounga leonina) from Antarctica.

Seven pairs of southern elephant seals (Mirounga leonina) pups and their dams were sampled during the late weaning season among a breeding population of seals on Elephant Island in Antarctica. The blubber of the pups and the milk and blubber of their dams were analyzed for lipid-normalized concentrations of PCBs and organochlorines compounds in order to evaluate the lactational transfer of these contaminants. The lipid-normalized concentrations in these tissues were in the ppb range (i.e., ngg(-1) lipid). The levels of contaminants in southern elephant seals were low in comparison with residues that have been reported in pinnipeds from the northern hemisphere. The relative tissue concentrations of the analytes measured followed the pattern: SigmaDDT>mirex>SigmaPCB>Sigmachlordane>HCB>heptachlor epoxide>dieldrin>methoxychlor>SigmaHCH>other organochlorines. The very high DDE/SigmaDDT ratio (0.91) in the blubber of dams and pups was an indicative of long-term, extremely distant pollution. On the other hand, the relatively high levels of some other organochlorine pesticides (e.g. mirex, heptachlor epoxide, dieldrin, methoxychor) may reflect the continued use of these insecticides in developing countries located in the southern hemisphere. For most of the analytes measured, the lipid-normalized concentrations were lower in pup blubber and in the milk than in the maternal blubber. Lactational transfer rates were dependent on the logK(ow) (octanol/water partition coefficient) values of the analytes measured, less lipophilic compounds being more readily transferred to the pups by the lactational route.

Residues of persistent organochlorine contaminants in southern elephant seals (Mirounga leonina) from Elephant Island, Antarctica.

Contamination of blubber tissues by organochlorine pesticides (OC) and PCBs was assessed in female and male pups and juveniles, as well as in adult females and subdominant adult males of the Southern elephant seal, Mirounga leonina, from Elephant Island in the Antarctic Peninsula. All residues of persistent organochlorine contaminants analyzed were found in blubber samples, except for beta-HCH, endosulfan II, endrin, heptachlor, and aldrin. The relative concentrations of the analytes detected were sigmaDDT > sigmaPCB > sigmachlordane > mirex > dieldrin > HCB> sigmaendosulfan > methoxychlor > sigmaHCHs > other OC pesticides. OC and PCBs concentrations were 1 or 2 orders of magnitude lower than those found in pinnipeds from northern hemisphere. The ratio sigmaDDT/sigmaPCB was higher in southern elephant seals. The relative importance of some OC residues indicates that pesticides used either currently or in the recent past in countries in the southern hemisphere are the sources of contamination in the Antarctic region. Data showed that concentrations of contaminants generally increased from pups < juveniles < adults and suggested that pups accumulated contaminants through transfer from the mother seals via transplacental and lactational routes.

Comparison between the antioxidant status of terrestrial and diving mammals.

Many diving mammals are known for their ability to deal with nitrogen supersaturation and to tolerate apnea for extended periods. They are all characterized by high oxygen-carrying capacity in blood together with high oxygen storage in their muscle mass due to large myoglobin concentrations. The above properties theoretically also imply a high tissue antioxidant defenses (AD) to counteract reactive oxygen species (ROS) generation associated with the rapid transition from apnea to reoxygenation. Different enzymatic (superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, and glutathione S-transferase), and non-enzymatic (levels of glutathione) AD as well as cellular damage (thiobarbituric acid-reactive substances contents, as a measure of lipoperoxidation) were measured in blood samples obtained from anesthetized animals, and also in blood obtained from recently dead diving mammals, and compared to some terrestrial mammals (n=5 in both groups). The results confirmed that diving mammals have, in general, higher antioxidant status compared to non-diving mammals. Apparently, to avoid exposure of tissues to changing high oxygen levels, and therefore to avoid an oxidative stress condition related to antioxidant consumption and increased ROS generation, diving mammals possess constitutive high levels of antioxidants in tissues. These data are in agreement with short-term AD adaptations related to torpor and to animals that experience large daily changes in oxygen consumption. These data are similar to the long-term adaptations of animals that undergo hibernation, estivation, freezing-thawing and dehydration-rehydration processes. In summary, animals that routinely face high changes in oxygen availability and/or consumption seem to show a general strategy to prevent oxidative damage by having either appropriate high constitutive AD and/or the ability to undergo arrested states, where depressed metabolic rates minimize the oxidative challenge.

Diving seals: are they a model for coping with oxidative stress?

The diving lifestyle of seals depends upon cardiovascular adjustments that result in frequent vasoconstriction of numerous organs. With the first post-dive breath, reperfusion allows for eliminating accumulated carbon dioxide (CO(2)) and reloading oxygen (O(2)) stores. Reintroduction of oxygenated blood raises the potential for production of reactive oxygen species (ROS) and the possibility that they may overwhelm the antioxidant defenses. This study addresses the question of possible adaptive responses that allow ringed seal (Phoca hispida) tissues to tolerate repeated cycles of ischemia and reperfusion, and thus protect them from oxidative insult. We obtained samples of ringed seal heart, muscle and kidney through the cooperation of native subsistence hunters at Barrow, Alaska. Samples were subjected to oxidative stress by addition of xanthine oxidase. Production of superoxide radical (O(2)(.-)), lipid peroxidation (as determined by the presence of thiobarbituric acid reactive substances, TBARS) and antioxidant capacity (AOX) were quantified by spectrophotometric analysis. Similarly treated pig tissues were anticipated to be more susceptible to oxidative stress. Contrary to expectations, pig tissues revealed less O(2)(.-) and TBARS compared with ringed seal tissues. These results show that ringed seal muscle, heart and kidney can be induced in vitro to generate ROS, and suggest that the living seal's protective defenses may depend upon O(2)(.-) production, similar to the protective effect of experimental preconditioning, or on enhanced intermediate scavenging, as evidenced by the larger AOX found in ringed seal tissues.

Postweaning duration and body composition changes in Southern elephant seal (Mirounga leonina) pups at King George Island.

Weaning mass in southern elephant seals is highly variable, the heaviest pups being three times as heavy as the lightest ones. After weaning, pups undergo an extensive postweaning period in which they draw on their reserves. To quantify the energy expenditure during the postweaning period, changes in mass, body composition, and postweaning duration were measured in southern elephant seals at King George Island, South Shetland Islands, Antarctica. Overall, mean pup weaning mass was 154 +/- 26 kg (n=117) and did not differ between sexes. Mean minimum postweaning duration was 42.5 +/- 7.5 d. Heavier animals at weaning had lower mass-specific mass loss rates than lighter ones, and a faster depletion of body reserves was associated with a shorter postweaning period. The proportion of body mass represented by fat at weaning was 37% +/- 4% (n=47) and did not differ between sexes. Of these pups, 36 were recaptured after a mean period of 36 d after weaning. On average, total mass loss measured in these animals (39 kg) was composed of 39% water, 47% fat, and 12% protein. The composition of mass loss was not significantly different between sexes and was not related to weaning mass or total body energy reserves. However, fatter animals at weaning lost more fat per kilogram lost than thinner ones. Late in the fast, males and females appeared to be in a similar body condition. Nevertheless, the overall proportion of body mass represented by fat at this time was lower than that presented by the same animals at weaning. We estimated that during the postweaning period pups lost, on average, 30% of their mass at weaning. This comprised approximately 35% of the energy and 32% of the fat in the pup's body.

Skin biopsy as a nondestructive tool for the toxicological assessment of endangered populations of pinnipeds: preliminary results on mixed function oxidase in Otaria flavescens.

The aim of this study was to develop and validate a method for assessing the toxicological risk of endangered populations of pinnipeds based on a nondestructive biological tool, the skin biopsy specimen. Skin biopsies can be obtained from pinnipeds by anaesthetising the animals and taking a small amount of skin in the anterior flipper area, or by shooting a biopsy dart with a crossbow. Skin biopsy material is suitable for a wide range of chemical and biomarker analysis. Organochlorines and polycyclic aromatic hydrocarbons can be analysed in subcutaneous fat and MFO activity (BPMO), Cyt.P450 isoforms, and DNA damage can be detected in epidermis.