Energy reserve utilization in northern elephant seal ( Mirounga angustirostris ) pups during the postweaning fast: size does matter (original) (raw)
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Functional Ecology, 2004
1. Organisms are forced to make trade-offs when allocating energy reserves during sustained periods of fasting. 2. For most animals, lipid catabolism is the preferred source of energy to safeguard important protein sources. However, marine mammals also have a compounding pressure to conserve some lipid stores. The main site of lipid storage in these animals is the blubber layer, which is not only an important energy source during fasting, but is also the primary thermal barrier when at sea. 3. To explain how the allocation of protein and lipid reserves during fasting are influenced by body condition (body mass and percentage lipid of total body mass), a dynamic state variable model that takes into account fitness consequences of different allocation strategies was developed. 4. This model was parameterized with respect to conditions faced by weaned Northern Elephant Seal (Mirounga angustirostris Gill) pups. It incorporates the independent effects of body mass and protein mass (the two state variables) on survival and the costs of utilizing either lipid or protein during the postweaning fast. 5. Predictions of lipid and protein allocation by the model were not significantly different from measurements on wild seals. Finally, the model showed that body lipid content and fasting duration both influence allocation of energy reserves.
Physiological and Biochemical Zoology, 2003
The fasting metabolism of 71-to 235-d-old subantarctic fur seal (Arctocephalus tropicalis) pups from Amsterdam Island, southern Indian Ocean, was investigated during the long foraging trips of their mothers. Body lipid reserves were proportionally greater in female than male pups and higher in postmoult (37%) than premoult (10%) animals. The mass-specific rate of mass loss did not differ between the sexes but was lower than observed in other species. Daily mass loss was estimated to 56% fat, 10% protein, and 34% water. The rate of protein catabolism (15 g d Ϫ1 ) was negatively related to the size of initial lipid stores and accounted for 9% )%1ע( of total energy expenditure. However, body composition changes during the fast were not equal between the sexes, with females relying more on protein catabolism than males (11% and 5% of total energy expenditure, respectively). Energy expenditure (270 kJ kg Ϫ1 d Ϫ1 ) and metabolic water production (11.5 mL kg Ϫ1 d Ϫ1 ) rates are the lowest reported for an otariid species. These results suggest that subantarctic fur seal pups greatly reduce activity levels to lower energy expenditure in addition to adopting proteinsparing metabolic pathways in order to survive the extreme fasts they must endure on Amsterdam Island.
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2009
Surviving prolonged fasting requires various metabolic adaptations, such as energy and protein sparing, notably when animals are simultaneously engaged in energy-demanding processes such as growth. Due to the intermittent pattern of maternal attendance, subantarctic fur seal pups have to repeatedly endure exceptionally long fasting episodes throughout the 10-mo rearing period while preparing for nutritional independence. Their metabolic responses to natural prolonged fasting (33.4 ± 3.3 days) were investigated at 7 mo of age. Within 4–6 fasting days, pups shifted into a stage of metabolic economy characterized by a minimal rate of body mass loss (0.7%/day) and decreased resting metabolic rate (5.9 ± 0.1 ml O2·kg−1·day−1) that was only 10% above the level predicted for adult terrestrial mammals. Field metabolic rate (289 ± 10 kJ·kg−1·day−1) and water influx (7.9 ± 0.9 ml·kg−1·day−1) were also among the lowest reported for any young otariid, suggesting minimized energy allocation to b...
Journal of Experimental Biology, 2007
This study used supplementary feeding to test the hypothesis that fuel partitioning during the postweaning fast in grey seal pups is affected by size and composition of energy reserves at weaning, and by extra provisioning. Mass and body composition changes were measured during suckling and fasting to investigate the effect of natural differences in energy reserves at weaning on subsequent allocation of fat and protein to energy use. We fed seven pups for 5 days after weaning, to investigate the effect of increased fuel availability, and particularly protein, on fuel utilisation. After correcting for protein used during the moult, the proportional contribution of fat was 86-99% of total energy use. Pups with greater energy reserves, i.e. those that were heavier and fatter at weaning, had higher rates of fat and energy use. There was no significant relationship between adiposity at weaning and proportional contribution of fat to energy use, perhaps due to a limited sample size or range of body masses and adiposity. Supplemented individuals used energy, specifically fat, much faster and utilised proportionally less of their endogenous protein by departure than non-supplemented individuals. Fat metabolism contributed a similar percentage to daily energy use in both groups. These findings show that pups spare protein, even when energy use is dramatically increased. Pups that receive greater maternal provisioning and lay down more protein may have increased survival chances at sea. This study highlights the importance of protein reserves in first year survival of grey seal pups.
Polar Biology, 2000
Deuterium-labeled water was used to measure changes in the proximate body composition during the lactation period and after weaning in southern elephant seal pups at King George Island, South Shetland Islands, Antarctica. During the lactation period (23.0 1.4 days) pups gained a mean of 4.9 0.5 kg/day (n 7). Of the total mass gain (112 8 kg), 38% was water, 48% was fat, and 11% was protein. This represented an increase in total body gross energy of 2437 145 MJ. The proportion of body mass represented by fat was less than 2% at birth, increasing to 35 2% at weaning. We followed the pups during a mean period of 36 3 days after weaning. During this period, pups had a mean loss of 1.21 0.10 kg/day (n 7) comprising 39% water, 48% fat, and 12% protein. The energy cost over this period was 952 168 MJ, which represented, on average, 39% of the total energy gained during the suckling period.
Physiological and Biochemical Zoology, 2003
In phocid seals, the transition to nutritional independence is abrupt, with females abandoning their offspring after weaning and returning to sea. We hypothesized that body size at weaning may play an important role in the nature of this transition. We studied the changes in body composition and water flux of newly weaning harbour seals over the first 4-6 wk postweaning. Thirty-three pups were dosed with deuterium oxide to estimate total body water (TBW) and a subset of 24 was dosed twice to estimate changes in body composition and water flux. All pups lost body mass over the study period, but TBW increased during the period of mass loss, indicating continued lean tissue growth. Combined data from this and our early study indicated that heavy (>median mass) pups were relatively fatter (41.0% vs. 37.1%) and had significantly greater total body energy at weaning than did light (< or = median mass) pups. Percentage TBW declined linearly over time in light pups but was constant in heavy pups for the first 19 d postweaning and then declined linearly. Both the temporal pattern and composition of mass loss differed between light and heavy pups. Estimated food intake increased in the second 2 wk of study compared to the first 2 wk, in both light and heavy pups, reflecting increased foraging success but at levels still insufficient to meet daily expenditures of most individuals.
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2015
Northern elephant seal pups were longitudinally sampled at Año Nuevo State Reserve during the post-weaning fast, in order to evaluate the changes of fatty acid (FA) profiles in serum as well as in the inner and outer layers of blubber. The major FAs of inner and outer blubber layers were broadly similar to those found in NES maternal milk previously measured, suggesting a direct deposit of dietary FAs in the blubber during the suckling period. The outer blubber layer contained more medium-chain monounsaturated FAs that contribute in keeping the fluidity of this tissue at cold temperatures. It was compensated by higher proportions of saturated FAs in the inner blubber layer. The FA signature of inner blubber, the layer that is mainly mobilised during energy deprivation, slightly differed from the signature of serum. There were greater proportions of medium-chain saturated FAs and ω-6 polyunsaturated FAs, and lower proportions of long-chain saturated FAs, medium-chain monounsaturated FAs and long-chain monounsaturated FAs in serum as compared to inner blubber. We also demonstrated that lipophilicity is the main factor governing the mobilisation of FAs from blubber. The least lipophilic FAs were preferentially hydrolysed from blubber, leading to an enrichment of the more lipophilic FAs in this tissue with the progression of the fast. The expression levels of HSL and ATGL, which are two enzymes involved in the lipolytic process, remained stable during the post-weaning fast. This suggests that the pups have developed the enzymatic mechanisms for an efficient lipolysis as soon as the first week of fast.
Physiological and Biochemical Zoology, 2008
Gray seals (Halichoerus grypus) undergo a terrestrial postweaning fast (PWF) that depletes energy reserves acquired during the suckling interval. Plasticity in PWF duration may ensure that pups of variable body condition depart for sea with adequate energy reserves. To test this hypothesis, we examined body condition of 30 gray seal pups at weaning and monitored their PWF duration. On average, fat accounted for 47.3% ע of their -kg weaning mass. Although fasting 0.7% 53.2 ע 1.3 duration averaged d ( ), there was considerable 21 ע 1.1 n p 28 variation in fasting duration (9 to 131 d) and the resulting age when pups departed to sea (26 to 149 d). Percent fat at weaning (38.6%-54.6%) was positively correlated with fasting duration ( , , ). In contrast, total body gross n p 28 r p 0.376 P p 0.0489 energy (735.3-1,447.4 MJ) and body mass (39.0-66.0 kg) were not correlated with fasting duration. Thus, body composition, not overall body reserves, predicted fasting duration, but the effect was weak, indicating that other factors also account for the observed variation in fasting duration. We speculate that pups with greater percent fat more effectively utilized lipid and conserved protein while meeting metabolic costs throughout the PWF. As a result, fatter pups extended the PWF duration, which may be critical for development of diving physiology and may have facilitated their survivorship to age 1.
Journal of Comparative Physiology B, 2013
Phocids routinely fast for extended periods. During these fasts, energetic requirements are met primarily through the catabolism of blubber lipid. To assess whether fatty acid (FA) composition changes during the postweaning fast in northern elephant seals, blubber biopsies were acquired longitudinally from 43 pups at 2.3 ± 1.5 and 55.2 ± 3.7 days postweaning in 1999 and 2000. At weaning, short-chain monounsaturated FA (SC-MUFA, B18 carbons) dominated the blubber while saturated FA (SFA) were found in the next highest proportion. The major FA (all C1 % by mass) comprised approximately 91 % of total blubber FA. In both years, 18:1n-9 and 16:0 were the most prevalent FA. Major FA mobilized during the fast consisted of polyunsaturated FA (PUFA), SFA, and SC-MUFA. Long-chain MUFA ([18 carbons) tended to be conserved. The fractional mobilization value of 20:5n-3 was the highest, resulting in significant reductions of this PUFA. Although concentrations of some blubber FA changed significantly during the postweaning fast, the general FA signature of blubber was similar at weaning and near the end of the fast. Changes in some FA differed across years. For example, the concentration of 20:4n-6, a minor PUFA, was significantly reduced in 1999 but not in 2000. FA mobilization patterns in northern elephant seal pups are somewhat similar to those reported previously for other fasting phocids and terrestrial mammals, though there are some notable differences. Differences in FA mobilization patterns across mammalian species may be related to differences in diets, geographical distribution, environmental factors, physiological adaptations, and life history stage. Keywords Blubber Á Catabolism Á Fasting Á Fatty acid Á Marine mammal Á Mobilization Communicated by H.V. Carey.