Biochemical aspects of pressure tolerance in marine mammals

Some marine mammals can dive to depths approaching 2000 m. At these hydrostatic pressures (200 atm), some fish species show alterations in enzyme structure and function that make them pressure-tolerant. Do marine mammals also possess biochemical adaptations to withstand such pressures? In theory, biochemical alterations might occur at the control of enzymatic pathways, by impacting cell membrane fluidity changes or at a higher level, such as cellular metabolism. Studies of marine mammal tissues show evidence of all of these changes, but the results are not consistent across species or diving depth. This review discusses whether the elevated body temperature of marine mammals imparts pressure tolerance at the biochemical level, whether there are cell membrane structural differences in marine mammals and whether whole, living cells from marine mammals alter their metabolism when pressure stressed. We conclude that temperature alone is probably not protective against pressure and that cell membrane composition data are not conclusive. Whole cell studies suggest that marine mammals either respond positively to pressure or are not impacted by pressure. However, the range of tissue types and enzyme systems that have been studied is extremely limited and needs to be expanded before more general conclusions about how these mammals tolerate elevated pressures on a biochemical level can be drawn.     

Isolation and purification of the IGF-I protein complex from rabbit seminal plasma: Effects on sperm motility and viability

A protein of about 150 kDa affecting sperm kinetic motility and viability was purified from rabbit seminal plasma. The incubation of rabbit sperm with this purified seminal plasma protein caused significant changes in sperm viability and motility. Moreover, the seminal protein showed a noticeable reactivating effect on immotile spermatozoa. A 10-mg amount of purified protein, added to immotile rabbit spermatozoa suspended in Tris-citrate, pH 7.4, resulted in a 48% reactivation. It is known that circulating insulin-like growth factors are bound to specific high-affinity binding proteins and form complexes with relative molecular masses of about 150 kDa. Western blotting analyses proved the existence of insulin-like growth factor in the protein purified from rabbit seminal plasma and immunofluorescence staining showed the existence of IGF-1 receptor in rabbit spermatozoa. Therefore, we suggest that the purified rabbit seminal plasma protein may represent the protein complex delivering IGF to the sperm cells thus affecting their physiological functions.     

Endocrine Changes in Harbor Seal (Phoca vitulina) Pups Undergoing Rehabilitation

Rehabilitating pinniped pups are often admitted to care centers as neonates and generally lack maternal investment and are in poor body condition. Upon admittance to a rehabilitation facility, pups are typically fed a milk replacement formula via gavage, which is switched to frozen fish upon weaning. While rehabilitation has been successful in terms of recovery and release, preweaning growth rates in captivity are consistently lower than in the wild. Indicators of stress (cortisol and total thyroxine; TT4), and standard morphometrics, of harbor seal pups in rehabilitation (n = 20) were determined for both preweaned and weaned pups. Hormone concentrations and standard morphometrics from pups in care were compared with free‐ranging harbor seal pups (n = 59). Pups in rehabilitation gained mass on both milk and fish diets. Preweaned pups had greater mean serum cortisol and similar TT4 concentrations than weaned pups. Free‐ranging harbor seal pups were heavier and longer than preweaned and weaned pups in rehabilitation. The free‐ranging pups had the lowest cortisol and highest TT4 concentrations of any of the pups. These results suggest that weaned pups that have undergone rehabilitation are not physiologically equivalent to free‐ranging weaned pups. Additional research is needed regarding physiological changes in endocrine values during early development under captive care conditions. This information should be useful to marine mammal rehabilitation centers in their development of care protocols and release criteria for rehabilitating harbor seal pups. Zoo Biol. 32:134–141, 2013. © 2012 Wiley Periodicals, Inc.     

Antarctic marine life under the McMurdo Ice Shelf at White Island: A link between nutrient influx and seal population

Summary Throughout 1981, the first routine collections of a variety of fish were made under the McMurdo Ice Shelf near White Island, Antarctica. Estimates of their local biomass were calculated using food consumption patterns of resident seals. Since no significant primary production occurs at White Island, the resident fauna must be maintained by a large nutrient influx from the Ross Sea.     

Changes in plasma fatty acids indicate change in nutritional status in developing Weddell seal pups

The concentrations and the fatty acid compositions (weight percent) of three plasma lipid fractions (phospholipids, cholesteryl esters, and triacylglycerols) were examined in five Weddell seal pups through suckling, the post-weaning fast and periods of independent foraging. The principal plasma fatty acids in Weddell seal pups during suckling were the same as those previously reported for milk samples collected from lactating Weddell seals. In contrast to the stable milk fatty acid composition suggested by the previous study, significant changes in the fatty acid composition of plasma lipids occurred during suckling. These included an increase in the weight% of 20:4(n-6) and 18:0 in phospholipids, an increase of 20:4(n-6) in cholesteryl esters, and an increase of 20:1(n-9) and a decrease of 20:5(n-3) in triacylglycerols. Weaning and the subsequent fasting period were accompanied by a dramatic drop in the plasma concentration and 14:0 content of triacylglycerols and by marked decrease and increase in the weight% of 20:1(n-9) and 20:5(n-3), respectively, in this lipid fraction. Weight% of 14:0 in triacylglycerols and/or plasma concentration of triacylglycerols clearly distinguish post-weaning from suckling. However, fasting versus foraging pups could not be clearly distinguished. Received: 7 October 1996 / Accepted: 20 May 1997