Northern Elephant Seal Pups Research Articles

Chylomicron triacylglycerol fatty acids in suckling northern elephant seals (Mirounga angustirostris) resemble the composition and the distribution of fatty acids in milk fat

Following birth, the northern elephant seal (Mirounga angustirostris) pups rapidly gain weight by ingesting milk with a high fat content, as much as 50%. To better understand the metabolism of the pups during the suckling period, the positional distributions of triacylglycerol fatty acids in both the milk and chylomicra were determined. Extracts of enzymatically digested lipids were separated by thin layer chromatography and the constituent fatty acids were separated and quantified by gas liquid chromatography. Over 84% of the fatty acids were either monoenoic or saturated, with the ratio of monoenoic to saturated fatty acids ranging between 2.9-4.0. Positional distributional analyses revealed that the very long chain monoenoics (20:1 and 22:1) were located primarily at the sn-1,3 positions of milk triacylglycerols. In the interval between the onset of lactation to the time of weaning, the content of these very long chain monoenoic fatty acids at the sn-1,3 positions increased from 13–37%. At the sn-2 position, the percentage of 18:1 was 3–5-fold higher than 16:1. Analyses indicated that the triacylglycerols in both milk and suckling pup chylomicra were similar. This particularly was true for the distributions at the sn-2 position, indicating that milk fats are being absorbed primarily via the 2-monoacylglycerol pathway.

Plasma melatonin concentration in neonatal northern elephant seals, Mirounga angustirostris

The development of pineal function in northern elephant seals was examined in an attempt to understand the physiological basis for previously observed high daytime levels of melatonin in neonatal southern elephant seals. Pineal glands from four northern elephant seal pups, estimated age less than 1 week, weighed 3.0 ± 0.80 g, which was significantly less than that previously found in southern elephant seals (4.6 ± 0.35 g). Midday concentrations of plasma melatonin in pups averaged more than 3000 pmol/l in the first 5 days post-partum, but declined rapidly to less than 400pmol/l after day 9. Daytime melatonin levels in northern elephant seals tended to be lower than in southern elephant seals, although they were very high compared with other species. A circadian cycle of plasma melatonin concentration was observed in newborn northern elephant seals, with levels of 3000–5000 pmol/1 during the day, rising to more than 10,000 pmol/1 late in the dark phase. Soon after weaning at 4 weeks of age, daytime and night-time levels were in the range 60–100 pmol/1 and 100–400 pmol/1, respectively. When approximately 10 weeks old, most samples were in the range 100–400 pmol/1 with no discernible difference between day and night levels. The results do not support the hypothesis that the pineal gland is involved in thermogenesis in new-born southern elephant seals. Instead, the very active pineal gland may contribute to energy conservation, by lowering body temperature, particularly at night. As physical insulation is acquired by the deposition of blubber, the mechanism is not required and melatonin falls to adult levels.

Developmental changes in cardiorespiratory patterns of sleep-associated apnea in northern elephant seals.

The development of heart rate and respiratory patterns related to sleep-associated apnea were studied in northern elephant seal (Mirounga angustirostris) pups and adult males. Heart rate patterns became more refined in conjunction with an age-related increase in apnea duration in pups. That is, older pups showed significant sinus arrhythmia, while breathing and apneic heart rate were both stable and similar in magnitude to the sinus arrhythmia minimum. By contrast, younger pups showed poor or nonexistent sinus arrhythmia and shorter apnea durations with a variable and/or high heart rate during apnea. Apnea duration was positively correlated with the development of sinus arrhythmia and negatively correlated with both eupneic and apneic heart rate. Adult males showed extremely well-developed patterns of sinus arrhythmia and, in all cases, the minimum heart rate during the sinus arrhythmia was lower than the average heart rate recorded during apnea. These results suggest that seal pups are not born with the cardiac control associated with voluntary long duration apnea, but that apnea tolerance increases with refined cardiorespiratory control.

Patterns of respiration and heart rate during wakefulness and sleep in elephant seal pups.

Although breath holding during diving has been studied extensively in seals, the recent observation that these mammals also exhibit long-duration apnea while apparently sleeping has not been systematically examined. This project examined sleep apnea in northern elephant seal pups (Mirounga angustirostris). The animals exhibited a sequential sleep pattern of wakefulness-slow-wave sleep (SWS)-rapid eye movement (REM) sleep that resembled the normal pattern of mammalian sleep. The typical respiratory pattern during sleep in 4-mo-old pups consisted of short periods of continuous breathing separated by periods of apnea of up to 12 min. Several cycles of apnea and eupnea could occur during a single sleep episode. Breathing during a sleep cycle occurred only in SWS, never during REM sleep. The eupneic heart rate was characterized by significant sinus arrhythmia, and the apneic heart rate was similar to the minimum value during normal sinus arrhythmia. Patterns of change in breathing and heart rate associated with wakefulness and sleep were similar in seals sleeping underwater and on land. When sleeping underwater, the seals raised their heads to the surface to breathe without awakening. The changes in heart rate associated with normal sinus arrhythmia, sleep apnea, and diving apnea appear to be similar, suggesting regulation by a common homeostatic control mechanism.

Water conservation and protein metabolism in northern elephant seal pups during the postweaning fast.

Urine production and N output were monitored in northern elephant seal (Mirounga angustirostris) pups progressing through 10 weeks of a natural postweaning fast. Urine output declined by 84% (to 69 +/- 12 ml.day-1) at 10 weeks (P < 0.05). Glomerular filtration rate at 10 weeks was 51% of the 67 +/- 3 ml serum.min-1 observed during week 1 (P < 0.05). Urine N excretion fell by 69% to 1.2 +/- 0.17 g.day-1, while urinary concentration increased (P < 0.05). Serum urea declined from an initial 11 mmol.l-1 to 5-7 mmol.l-1 by 5 weeks. The fall in urinary N loss (and thus amino acid oxidation) was concomitant with depressed metabolic rate. Therefore, protein contributed little toward meeting energy demands (i.e., < 4% of average metabolic rate) throughout fasting. These data indicate that fasting pups improve water conservation and minimize protein catabolism during prolonged natural fasts without an exogenous source of water.

Estimation of Splenic Volume and Its Relationship to Long-Duration Apnea in Seals

Splenic volume was estimated in northern elephant seal pups (Mirounga angustirostris) by calculating the reservoir volume required to accommodate measured shifts in hematocrit that occur during periods of sleep-associated apnea. In vivo total estimated splenic mass for 15 pups represented 2.8% of body mass, while adult female seal splenic mass was estimated to be between 7.3% and 10.5% of body mass, considerably higher than that of terrestrial mammals. The model was applied to several other species of pinnipeds. Splenic mass estimates by this method were in agreement with previously reported values obtained for some pinniped species by computerized axial tomography (CT) scan. The data suggest that splenic mass in seals is correlated to the blood volume to body mass ratio and that the large spleen of seals is an anatomical consequence of the increased phocid blood volume.

Maternal Energy Investment in Elephant Seal Pups: Evidence for Sexual Equality?

Labeled water methodology was used to quantify maternal energy investment in northern elephant seal (Mirounga angustirostris) pups. Pup milk intake, field metabolic rate, mass change, and body composition were monitored during the nursing period and throughout the postweaning fast. Maternal investment did not vary significantly as a function of pup sex. There was no evidence for sex differences in growth rate or milk intake rate, and mean metabolic rate of suckling pups did not differ significantly between the sexes. Males and females appeared to be in similar condition at the end of the postweaning fast, just prior to their first trip to sea. Some male pups may attain greater size relative to females without additional cost to their mothers. These data do not provide evidence to reject R. A. Fisher's theory of equal investment in the sexes.

Changes in Standard Metabolism during Long-Term Fasting in Northern Elephant Seal Pups (Mirounga angustirostris)

Measurements of body mass, body composition, and O₂ consumption rate V̇o2 were used to quantify some of the factors that influence metabolism during the first 4 mo of development in the northern elephant seal pup. During the 4-wk nursing period, average body mass of the pups increased from 42.0 ± 3.5 kg to 127.3 ± 15.9 kg. By the end of the 10-wk postweaning fast mean body mass declined to 83.1 ± 1.5 kg. Body fat increased from 4% of body mass near birth to approximately 48% at weaning but remained relatively constant throughout the fast. Dramatic changes in body mass and body composition such as these would be expected to influence metabolism significantly. To test this theory, O₂ consumption was measured in pups from birth to 18 wk of age through open-circuit respirometry. Changes in metabolism were correlated most strongly with increases in lean body mass (r² = .51, P < 0.01). Together, changes in lean body mass and age accounted for 75% of the variability seen in V̇o2 (P < 0.01). In addition, a 19% increase in lean mass-specific V̇o2 was documented with the onset of feeding in two laboratory animals, after a 10-wk postweaning fast. This implies a depression of metabolism, possibly as an adaptation for energy conservation during long-term fasting.

Sexual Behavior of Male Northern Elephant Seals: III. the Mounting of Weaned Pups

Abstract 1. Up to 50% of weaned northern elephant seal pups, Mirounga angustirostris, present on the Año Nuevo mainland rookery at the end of the breeding season showed evidence (tooth marks and injuries on the neck) of having been mounted by males. 2. Male-inflicted injuries on weanlings ranged from superficial tooth marks to deep gashes and punctures that bled and exposed the blubber. Most marks were superficial. 3. Approximately 0.5 % of all weaned pups died on the rookery from 1969-1990; about 35 % of the dead weanlings showed physical evidence that they were killed by males and males were suspected of having killed most of the rest. 4. Males mounting weanlings displayed many behaviors that are characteristic of male sexual behavior toward adult females and most weanlings responded like non-estrous females. Weanling mounts lasted an average of 2.8 min (N = 81) and were usually terminated when the male did not pursue an escaping weanling. There was no bias in the sex or the size of mounted weanlings. 5. Males also mounted conspecific juveniles (one and two years old), although these interactions were relatively infrequent because most juveniles were at sea during the breeding season. The behavior of males and juveniles during mounting attempts was qualitatively similar to weanling mounts; rarely, yearlings were killed by males. 6. Most mounters (91 %) were subadult males and were observed to mount weanlings only once in a breeding season. Occasionally, a male persisted in mounting weanlings repeatedly, within a season and across years. Weanling mounters did not differ from other males in their proximity to harems or in their copulatory success. 7. The proximate factors leading to weanling mounts appear to be male sexual inexperience, high libido, limited access to adult females, and stimulus generalization. Functionally, male sexual behavior toward weanlings appears to be a low-cost by-product of high male sexual motivation that may enhance a male's reproductive success. Weanlings exhibit behaviors, such as grouping into pods, seeking microhabitat refuges, and resisting mounts, that may reduce the chance of being mounted by a male or of being injured during a mounting attempt.

Circulatory water concentration in suckling and fasting northern elephant seal pups

This study examined circulatory water concentrations in the neonatal northern elephant seal (Mirounga angustirostris) in order to determine how suckling and fasting would alter the percentage of water in the whole blood, plasma, and red blood cells (RBC). Plasma water concentration dropped by about 3% during suckling and recovered about 1% during the fast (92.38 +/- 0.48% less than 1 week old, 90.15 +/- 0.36% weaning, 91.02 +/- 0.68% end of fast). RBC water values during this time were more variable than plasma values: RBC water increased about 1% during the first 2 weeks of suckling (from 67.80 +/- 0.28% to 68.68 +/- 0.51%) but dropped to slightly below original neonatal values by weaning (67.15 +/- 0.63%). The first several weeks of fasting were marked by wide variability in RBC water, but by the end of the fast RBC water was comparable to that at weaning. These results indicate: 1) Northern elephant seal pups do not exhibit circulatory dehydration during 10 weeks of fasting; 2) Measurements of plasma or RBC metabolites (such as plasma glucose or RBC hemoglobin) may show variations or trends due not to metabolic regulation but rather to changes in circulatory water concentration.

Relationships between plasma ketones and fasting duration in neonatal elephant seals

Long-duration fasting in mammals can ultimately lead to stage three terminal starvation, which is characterized by depleted fat stores, a metabolic shift away from fat metabolism toward lean tissue catabolism, and a sharp decline in circulating levels of plasma fatty acids and ketone bodies. However, this biochemical shift has never been observed outside of the laboratory in a naturally fasting, nonhibernating mammal. In the current study, plasma levels of the ketone body D-beta-hydroxybutyrate (beta-HBA) were assayed in 10 Northern elephant seal pups during suckling and the postweaning fast and in 12 fasting adult seals. Plasma beta-HBA concentration in the pups was minimal during suckling (0.09 +/- 0.06 mM; n = 10) and began to increase immediately after weaning. The concentration rose until about 55 days into the fast (1.34 +/- 0.36 mM; n = 10) and then declined sharply. Within 10 days of this deflection point, the seal pups left for sea. By contrast, adult elephant seals showed consistently low levels of beta-HBA after several months of fasting (0.06 +/- 0.07 mM; n = 12). The data suggest that the duration of fasting in elephant seal pups may be determined, in part, by biochemical shifts that occur near the end of the fast and that the regulation of ketone concentration is different in fasting neonatal and adult elephant seals.

Milk Intake of Elephant Seal Pups: An Index of Parental Investment

Total milk ingested throughout nursing in free-living northern elephant seal pups, derived from the turnover of tritiated water, gives an accurate estimate of the energetic component of parental investment. In 4 wk of nursing, females transferred a mean of 138 kg of milk with a value of 6.04 x 105 kcal, five times the metabolic requirements of pups. The mean rate of energy transfer is more than twice that predicted for the female's size from studies of laboratory and domestic animals. In one month, pups receive sufficient energy and essential nutrients from mother's milk to enable them to fast while continuing to develop for an additional 2 1/2 mo before feeding on their own. Measurement of the energetic component of parental investment makes it possible to test predictions from the theory of parental investment.

Demography of Northern Elephant Seals, 1911-1982

Northern elephant seals (Mirounga angustirostris) were hunted to near extinction in the 19th century. Protection has allowed them to recolonize former habitat on islands off California, where the population is increasing more than 14 percent per year. Immigration of young pregnant females from Baja California initiated the California rookeries but is responsible for only a small part of recent population growth. Almost 25,000 northern elephant seal pups were born in the species' range in Mexico and the United States in 1982 in comparison with only six known births in 1911.

Northern elephant seal development: The transition from weaning to nutritional independence

1. The 2 1/2-month period from weaning to departure from the rookery was studied in northern elephant seal pups at Ano Nuevo Island, California. After being weaned at 4 weeks of age, pups fast completely while learning to swim and dive before going to sea in search of food. 2. Pups increase their birthweight by a factor of 3–7 times on mother's milk alone. Males weigh more than females at birth and at weaning, and are nursed an average of one day longer. 3. Some newly weaned pups prolong the suckling period by stealing milk from nursing females or by being adopted by foster mothers. Males are more persistent and more successful at milk stealing than females and, consequently, exceptionally large weaners are always males. These sex differences are predicted from the manner in which adults maximize their reproductive success. An advantage in size and condition benefits a male much more than a female. Molting and canine eruption occur later in males than in females and these differences may be an adaptation in the former which facilitates milk stealing. 4. Sexual differentiation is evident in the earliest social interactions. Males interact more frequently than females and their bouts last longer. Behavioral components in the interactions of males and females resemble those of fighting adults of each respective sex. 5. Weaners begin entering the water when 6–7 1/2 weeks old. They learn to swim and dive gradually. As swimming proficiency increases, they venture further away from their birthplace. They are excellent swimmers and can stay underwater for 15 min by the time they leave the rookery at 3–3 1/2 months of age. 6. Although pups are born over an 8-week period, the majority of them depart the rookery over a 3-week period. Pups weaned late in the breeding season are stimulated to enter the water by those weaned earlier. Departure from the rookery is correlated with the onset of coastal upwelling and the latter is correlated with food abundance in the ocean. 7. Few weaned pups die before leaving the rookery. Mortalities result from injuries inflicted by adult males and females, trauma or drowning due to storms and high surf, overheating, accidents, and shark predation. 8. Survival after the first period at sea to 7 months of age is at least 50%. Thereafter, the survival rate declines gradually to a minimum of 12% at 3 years of age. There are no sex differences in survival to age 2. Pups born early in the breeding season exhibit a higher survival rate during the first year than those born later in the season; females born early in the season exhibit the highest parity rate in their cohort at age 3. 9. Early sex differences are interpreted as subserving the different adult reproductive strategies of each sex.

Comparative thermoregulation of suckling and weaned pups of the northern elephant seal, Mirounga angustirostris

1. 1. Surface heat loss and metabolic rate were measured in suckling and weaned northern elephant seal pups under rookery conditions. Laboratory measurements of heat flow through pelts from both age groups were also measured and insulation values calculated. 2. 2. The combination of wind and rain or surf spray yielded the highest heat loss values while intense solar radiation and no wind produced the lowest values from either group in the field. 3. 3. The range of insulation values measured from the pelts of suckling pups (0.031–0.114°C m 2/W) were well below the values measured from pelts of weaned pups (0.140–0.406 °C m 2/W). 4. 4. Suckling pups have a higher metabolic rate (26.7–31.5 VO 2 ml/min·kg 0.75) than weaned northern elephant seal pups and adults of other seal species.

Post‐mortem studies of Northern elephant seal pups

Thirty‐four pups of the Northern elephant seal, Mirounga angustirostris, collected from Mexican and Californian coastal islands were studied to determine causes of death, growth of certain organs, and development of the supernumerary bones of the occiput. Dead pups from Añ Nuevo Island off central California from 1965 through 1969 appear to have died due to crushing by adults, probably the large breeding bulls. Recent deaths through the 1972 breeding season indicate that some deaths are attributable to bites inflicted by agitated cows. Organ weights were taken on several pups and compared with weights recorded for pups of the Southern elephant seal. Some organs appear to grow proportional to body weight, and other organs show disproportionate growth. The supernumerary bones of the occiput called “extraoccipitalia” were found to be embryonically preformed in cartilage. Ossification centres were shown to be developing in late term foetuses. These extraoccipitalia evidently allow rapid growth of the neurocranium during the first few months postpartum and later fuse with adjacent cranial bones at about one year of age. The rising elephant seal population in relation to the types of mortality is discussed in relation to available breeding grounds.

Perinatal behavior of northern elephant seal females and their young.

Northern elephant seal females and pups were observed during four breeding seasons at Ano Nuevo Tstand, California. Six to seven days after a female arrived on the rookery she gave birth to a single pup which she nursed for four weeks. Estrus began 24 days after parturition and lasted an average of four days. Females spent a total of 34 days on the rookery before returning to sea. The only other time females came ashore was to moult, a period which lasted a few weeks. Most births occurred in the harem at night during the last two weeks of January. Cephalic presentations were more frequent than caudals (62% vs. 38%) and both were equally rapid. The placenta was delivered immediately after the pup or within an hour after birth. Stillbirths were infrequent and premature pups were never observed. The sex ratio was 49.4 males to 50.5 females. Eight females gave birth for the first time during their third year but most females are believed to give birth later. Three females gave birth on a different rookery than their own birthplace. The time of parturition from year to year was very consistent in individual females. Newborn pups weighed 65 lbs at birth and were 60 inches long. They are precocial and suckled for about four weeks before being weaned. Weaners moulted their natal pelage at four to six weeks of age, a time when they began entering the water. Most weaners left the rookery headed north during the month of April. Females accepted a pup by allowing it to nurse and rejected alien pups by biting them. Females emitted two vocalizations : a pup attraction call and a threat vocalization. Pups emitted a single vocalization which functioned in several situations. Scventy-two percent of the females observed nursed their own pups to weaning and rejected most of the suckling attempts of alien pups. A few females nursed an alien pup in addition to their own. Twenty-six percent of the females became separated from their pups or their pups died. One third of these females adopted an alien pup. Females that gave birth, but did not nurse for several days, did not copulate. The frequency and duration of suckling increased as pups developed. Pups attempted to suckle any available female but were rejected by most alien females. Sixty percent of marked pups suckled their mothers. The remaining forty percent were separated from their mothers and most of them died. Those that survived were adopted by an alien female or were suckled by several different females each day. Pup mortality at Ano Nuevo Island was very consistent over the four year period, ranging from 13.0% to 14.5%. Most mortalities were socially induced; pups separated from their mothers starved or were injured by adult males and females. The probability of separation was increased by high numbers of females and disturbances created by intrusions of breeding hulls into the harem.