Use of phylogeny to resolve the taxonomy of the widespread and highly polymorphic African giant shrews (Crocidura olivieri group, Crocidurinae, Mammalia)

The aim of this study is to provide a better understanding of the genetic relationships within the widespread and highly polymorphic group of African giant shrews (Crocidura olivieri group). We sequenced 769 base pairs (bp) of the mitochondrial cytochrome b gene and 472 bp of the mitochondrial control region over the entire geographic range from South Africa to Morocco. The analyses reveal four main clades associated with different biomes. The largest clade occurs over a range covering Northwest and Central Africa and includes samples of C. fulvastra, C. olivieri, and C. viaria. The second clade is composed of C. goliath from Gabon, while South African C. flavescens, and C. hirta form two additional clades. On the basis of these results, the validity of some taxa in the C. olivieri group should be re-evaluated.     

No evidence for a trade-off between reproductive investment and immunity in a rodent

Life history theory assumes there are trade-offs between competing functions such as reproduction and immunity. Although well studied in birds, studies of the trade-offs between reproduction and immunity in small mammals are scarce. Here we examined whether reduced immunity is a consequence of reproductive effort in lactating Brandt's voles (Lasiopodomys brandtii). Specifically, we tested the effects of lactation on immune function (Experiment I). The results showed that food intake and resting metabolic rate (RMR) were higher in lactating voles (6≤ litter size ≤8) than that in non-reproductive voles. Contrary to our expectation, lactating voles also had higher levels of serum total Immunoglobulin G (IgG) and anti-keyhole limpet hemocyanin (KLH) IgG and no change in phytohemagglutinin (PHA) response and anti-KLH Immunoglobulin M (IgM) compared with non-reproductive voles, suggesting improved rather than reduced immune function. To further test the effect of differences in reproductive investment on immunity, we compared the responses between natural large (n≥8) and small litter size (n≤6) (Experiment II) and manipulated large (11-13) and small litter size (2-3) (Experiment III). During peak lactation, acquired immunity (PHA response, anti-KLH IgG and anti-KLH IgM) was not significantly different between voles raising large or small litters in both experiments, despite the measured difference in reproductive investment (greater litter size, litter mass, RMR and food intake in the voles raising larger litters). Total IgG was higher in voles with natural large litter size than those with natural small litter size, but decreased in the enlarged litter size group compared with control and reduced group. Our results showed that immune function is not suppressed to compensate the high energy demands during lactation in Brandt's voles and contrasting the situation in birds, is unlikely to be an important aspect mediating the trade-off between reproduction and survival.     

黑线仓鼠繁殖输出与基础代谢率的关系

为了解黑线仓鼠繁殖输出与基础代谢率(BMR)的关系,阐明最大持续能量收支(SusMR)的限制水平, 揭示哺乳期能量收支对策,本文测定了哺乳期黑线仓鼠的体重、摄食量、BMR 和身体组成,以及哺乳期的胎仔数、胎仔重和泌乳能量支出(MEO)。结果显示,黑线仓鼠哺乳期体重降低了15.0 ± 0.8% , 摄食量显著增加, 哺乳高峰期平均摄食量为13.9 ± 0.3 g /d, 摄入能为222.1 ± 5.3 kJ/ d, 比哺乳初期增加121% , 比对照组高288% ;哺乳高峰期MEO 为62.4 ± 2.3 kJ/ d, 哺乳末期BMR 为49.7 ± 1.1 kJ/ d; 断乳时平均胎仔数4.7 ± 0.2、窝胎仔重50.5 ±1.6 g; 哺乳末期BMR 比对照组增加48% ,BMR 与消化系统各器官的相关性高于对照组; BMR 与胎仔数、胎仔重、乳腺重量和MEO 显著正相关。结果表明:初次繁殖的黑线仓鼠哺乳期SusMR 限制为4.47 ×BMR, 在自身维持和繁殖输出之间采取了“权衡分配”的原则,通过体重降低以减少BMR 的增加幅度, 从而有利于繁殖输出。     

Energetic strategies of shrews: ecological constraints and evolutionary implications

Data on various features influencing resource acquisition and allocation of energy in Soricidae are reviewed. The relationships between these features are examined at the three functional levels that constrain the energetic design of shrews: the maintenance of homeostasis (rate of metabolism and temperature regulation), the balancing of the energy budget (e.g. the influence of body mass, activity rate, various energy saving mechanisms and home range size), and the allocation of energy towards reproduction (e.g. the influence of litter size). Two major contradictory energetic designs may be recognized: one rather expensive design that is observed in cold and temperate climates with relatively predictable fluctuations in resource availability (e.g. in Sorex and Neomys ), and another much less expensive design that is observed mainly in warm or unpredictable environments (e.g. in Crocidura, Suncus and Notiosorex). It is speculated that climate and resource availability impose narrow limits on the evolution of these energetic strategies, mainly because of the small thermal inertia and reduced energetic autonomy of shrews.     

Oxidative Damage Does Not Occur in Striped Hamsters Raising Natural and Experimentally Increased Litter Size

Life-history theory assumes that animals can balance the allocation of limited energy or resources to the competing demands of growth, reproduction and somatic maintenance, while consequently maximizing their fitness. However, somatic damage caused by oxidative stress in reproductive female animals is species-specific or is tissue dependent. In the present study, several markers of oxidative stress (hydrogen peroxide, H₂O₂ and malonadialdehyde, MDA) and antioxidant (catalase, CAT and total antioxidant capacity, T-AOC) were examined in striped hamsters during different stages of reproduction with experimentally manipulated litter size. Energy intake, resting metabolic rate (RMR), and mRNA expression of uncoupling protein 1 (UCP₁) in brown adipose tissue (BAT) and UCP₃ in skeletal muscle were also examined. H₂O₂ and MDA levels did not change in BAT and liver, although they significantly decreased in skeletal muscle in the lactating hamsters compared to the non-reproductive group. However, H₂O₂ levels in the brain were significantly higher in lactating hamsters than non-reproductive controls. Experimentally increasing litter size did not cause oxidative stress in BAT, liver and skeletal muscle, but significantly elevated H₂O₂ levels in the brain. CAT activity of liver decreased, but CAT and T-AOC activity of BAT, skeletal muscle and the brain did not change in lactating hamsters compared to non-reproductive controls. Both antioxidants did not change with the experimentally increasing litter size. RMR significantly increased, but BAT UCP₁ mRNA expression decreased with the experimentally increased litter size, suggesting that it was against simple positive links between metabolic rate, UCP₁ expression and free radicals levels. It may suggest that the cost of reproduction has negligible effect on oxidative stress or even attenuates oxidative stress in some active tissues in an extensive range of animal species. But the increasing reproductive effort may cause oxidative stress in the brain, indicating that oxidative stress in response to reproduction is tissue dependent. These findings provide partial support for the life-history theory.     

Variation in oxygen consumption of the western diamondback rattlesnake (Crotalus atrox): implications for sexual size dimorphism

Variation in metabolism affects energy budgets of individuals and may serve as a mechanism that influences variation at whole organism or population levels. For example, sex differences in metabolic expenditure may contribute to bioenergetic sources of sexual size dimorphism. We measured oxygen consumption rates of 48 western diamondback rattlesnakes (Crotalus atrox) from a sexually dimorphic population and tested the effects of body mass, body temperature and time of day, in three groups of snakes: males, non-reproductive females, and vitellogenic females. Metabolic rates of male and non-reproductive female C. atrox were similar to rates reported for other rattlesnakes (mass exponents ranging from 0.645–0.670). Oxygen consumption was affected by body mass, body temperature and time of day, and was approximately 1.4 times greater in vitellogenic females than in non-reproductive females. No differences were found between males and non-reproductive females. Accordingly, differences in metabolic rate apparently do not contribute directly to sexual dimorphism in this population. Nevertheless, estimates of size-dependent maintenance expenditure lead us to hypothesize that adult female body size may represent a compromise between selection for increased litter size (accomplished by increasing body size), and selection for increased reproductive frequency (accomplished by decreasing body size, and, therefore inactive maintenance expenditure); this is a mechanistic scenario suggested previously for some endotherms. Accepted: 20 May 1998     

Meeting the energy demands of reproduction in female koalas,<Emphasis Type="Italic"> Phascolarctos cinereus</Emphasis>: evidence for energetic compensation

Koalas are generally considered to be limited by their ability to acquire energy from their diet of Eucalyptus foliage and have the lowest mass-specific peak lactational energy output measured in any mammal to date. This study considered the energetics and sources of energy utilised for reproduction in free-ranging female koalas. Energy requirements and foliage intake were greater in both lactating and non-lactating females in winter than summer, presumably due to demands of thermoregulation. Koalas met the peak energy requirements of lactation primarily by a 36% increase in their intake of foliage. Metabolic energy expenditure (field metabolic rate, 1778 kJ.day^–1 for a 6.25-kg female at the time of peak lactation) was not elevated during lactation. This was due to compensation for part of their lactational demands by reduction of another, non-reproductive, component of their energy budget. The observed energetic compensation was probably due primarily to substitution of the waste heat from the metabolic costs of milk production and increased heat increment of feeding for thermoregulatory energy expenditure. There may also have been energetic compensation by reduction of some aspect of maintenance metabolism. Such energetic compensation, together with the strategy of spreading lactation over a long period, minimises the magnitude of lactational energy demands on koalas, and thus the increase in daily food intake required during lactation. As the nutritional requirements of females at peak lactation are the highest of any members of the population, low reproductive requirements effectively increase the types and amount of habitat able to support koala populations.Abbreviations FMR field metabolic rate - HIF heat increment of feeding - RMR resting metabolic rate - _O2 rate of oxygen consumptionCommunicated by I.D. Hume     

黑线仓鼠断乳后能量代谢和脂肪累积的适应性调节

小型哺乳动物能量代谢和脂肪累积的适应性调节是其应对自然环境变化的主要能量学策略,但在不同的生活史阶段,脂肪组织适应性调节的特征和能量机理尚不清楚。为探讨不同繁殖阶段能量代谢和脂肪累积的变化及其内分泌机理,本文测定了黑线仓鼠哺乳期和断乳后摄食量、脂肪重量,以及血清瘦素水平、下丘脑瘦素受体（Ob-Rb）和相关神经肽的基因表达。结果显示,哺乳高峰期黑线仓鼠的脂肪重量几乎降低至零,断乳后显著增加;与非繁殖对照组相比,皮下脂肪、肾周脂肪与腹腔脂肪重量分别增长了1.5倍、37.1倍和1.9倍。断乳后摄食量、血清瘦素水平显著高于非繁殖对照组,Ob-Rb基因表达显著下调,而促食与抑食神经肽的基因表达均未发生显著变化。哺育不同胎仔数的黑线仓鼠在断乳后能量摄入、静止代谢率、身体组分未出现显著差异。研究表明,在不同的繁殖阶段脂肪累积呈现显 著的适应性调节,瘦素抵抗是断乳后脂肪累积补偿性增长的重要内分泌机制之一。这对迅速恢复脂肪累积,以应对将来的能量需求增加或者食物资源短缺的环境,进而提高自身的适合度具有重要意义。     

Short-term versus long-term effects of food intake on reproductive output in a viviparous snake, Vipera aspis

Feeding rates influence reproductive output in many kinds of animals, but we need to understand the timescale of this influence before we can compare reproductive energy allocation to energy intake. A central issue is the extent to which reproduction is fuelled by long-term energy stores ("capital" breeding) versus recently-acquired resources ("income" breeding). Our data on free-living aspic vipers show that there is no simple answer to this question: reproductive frequency is determined by long-term energy stores, offspring size is influenced by maternal food intake immediately before ovulation, and litter size is influenced by both long-term stores and short-term energy acquisition. Thus, offspring size in free-living vipers reflects the mother's energy balance over the preceding year (via a trade-off between litter size and offspring size) as well as her energy balance in the current breeding season. Hence, different components of a given reproductive output (litter) are not only functionally linked, but also respond to different temporal scales of prey availability. A female's body size has little effect on her reproductive output. Attempts to quantify reproductive energy allocation must take into account the fact that different reproductive traits (such as offspring size versus number) may respond to energy availability over different timespans. Thus, although the aspic viper is a typical "capital breeder" in terms of its reliance on stored reserves for maternal "decisions" concerning reproductive frequency, it is to some degree a facultative "income breeder" with respect to the determination of offspring size and litter size.     

Energetics of offspring production: a comparison of a marsupial (Monodelphis domestica) and a eutherian (Mesocricetus auratus)

This study compares the energetic cost of reproduction during gestation and lactation of a eutherian, the golden hamster (Mesocricetus auratus), and a similar-sized (60–120 g) marsupial, the gray short-tailed opossum (Monodelphis domestica). Food consumption was monitored in 20 reproductively active (RA) opossums and 16 RA hamsters from conception to weaning and at equivalent intervals in 19 non-reproductive (NR) opossums and 21 NR hamsters, all maintained within their zone of thermoneutrality (30 °C). Total energy assimilated from conception to weaning [opossums: 1261.3 ± 28.0 Kcal (1 Kcal = 4.1868 J) and hamsters: 1647.5 ± 60.6 Kcal] was positively correlated with litter size and mass per young in both species. Maternal mass-specific assimilated energy was significantly greater in hamsters than in opossums during gestation (P < 0.001), but not during lactation or from conception to weaning (P > 0.05). Efficiency of offspring production (energy stored in young/incremental energy in RA females) was higher in hamsters than in opossums and, in both species, it was higher during lactation than in gestation. The energetic cost of reproduction (per young per day) was higher in hamsters than in opossums. The marsupial mode of reproduction, as seen in opossums, yields young at lower cost but requires a longer reproductive period than is the case for a similar-sized eutherian. Accepted: 8 September 1998     

Energy budget during four successive bouts of lactation in striped hamsters exposed to decreases in ambient temperature

A prediction of the seasonal investment hypothesis is that overall energy investment needs to be greater for young being produced at colder temperatures. Then, that energy cost is lower as temperature becomes warmer. To evaluate this assumption, I performed a series of measures of food intake and reproductive output throughout four successive bouts of lactation in striped hamsters (Cricetulus barabensis) exposed to a constant warm temperature (Warm, 21°C) or exposed to consecutive decreases in ambient temperatures from warm to cold (Warm-Cold, 30-0°C). Warm hamsters showed similar asymptotic food intake, litter size and mass over the course of four successive bouts of lactation. Warm-Cold females consumed more food, but raised lighter litters during the third bout than first bout of lactation. Ambient temperatures had significant effects on energy budget and reproductive output, by which resting metabolic rate, nonshivering thermogenesis and activity of cytochrome c oxidase (EC 1.9.3.1) of brown adipose tissue were increased, but reproductive output was decreased with declines of temperatures. These findings suggest that a trade-off occurs between different components of energy expenditure during the successive course of four bouts of lactation. Seasonal hamsters decrease their reproductive output, but increase the energy spent on thermogenesis as the ambient temperature becomes colder. It may also indicate that temperature has a direct effect on metabolism, leading to an increase in overall energy expenditure at lower temperatures.     

Short- and long-term effects of litter size manipulation in a small wild-derived rodent

Iteroparous organisms maximize their overall fitness by optimizing their reproductive effort over multiple reproductive events. Hence, changes in reproductive effort are expected to have both short- and long-term consequences on parents and their offspring. In laboratory rodents, manipulation of reproductive efforts during lactation has however revealed few short-term reproductive adjustments, suggesting that female laboratory rodents express maximal rather than optimal levels of reproductive investment as observed in semelparous organisms. Using a litter size manipulation (LSM) experiment in a small wild-derived rodent (the common vole; Microtus arvalis), we show that females altered their reproductive efforts in response to LSM, with females having higher metabolic rates and showing alternative body mass dynamics when rearing an enlarged rather than reduced litter. Those differences in female reproductive effort were nonetheless insufficient to fully match their pups’ energy demand, pups being lighter at weaning in enlarged litters. Interestingly, female reproductive effort changes had long-term consequences, with females that had previously reared an enlarged litter being lighter at the birth of their subsequent litter and producing lower quality pups. We discuss the significance of using wild-derived animals in studies of reproductive effort optimization.     

Age-specific reproductive performance of female polar bears (Ursus maritimus)

Age-specific patterns of maternal weight, litter size, litter weight and reproductive effort were investigated for polar bears ( Ursus maritimus ) from western Hudson Bay. Most relationships were described by quadratic equations. Maternal weight in spring and autumn increased until 17 and 15 years of age, respectively, and then declined. Age-related increases in maternal weight were thought to be associated with improving hunting skills. The relationships between age and litter size, litter weight and reproductive effort, in both the spring and autumn, increased until 14 to 16 years, followed by a decline. We speculate that age-related decreases in reproductive performance are due to undetennined processes associated with ageing that impair the accumulation of fat stores necessary for reproduction. Pregnant females lost an average of 127 kg overwinter which represented an average of 43.5% of their autumn weight. Fat stores remaining after the overwinter fast may be critical for maintaining an energy supply to cubs once they return to the sea ice where the distribution and abundance of their prey is unpredictable. We suggest that maternal condition is an important factor contributing to lifetime reproductive success in polar bears.     

The relationship between size,budding rate,and growth efficiency in three species of hydra

Three species of the fresh water carnivore hydra, H. littoralis, H. pseudoligactis, and C. viridissima present a graduation in size with the first species the largest and albino Chlorohydra the smallest. When presented with a daily overabundance of food (artemia), considerable variation in food intake and gross efficiency of growth (proportion of food energy consumed that is turned into new protoplasm or buds) existed among the species. The degree of association between size of species and food intake was highly significant. However, budding efficiency among the species was found to be independent of food intake (when the effects of species size were eliminated) and of species size (when the effects of food intake were removed). However, species with high (low) efficiencies have significantly higher (lower) reproductive rates. A lowering of the temperature from 25° to 15° C. increased the size of the species, increased food intake, but decreased reproductive rate. In all species except H. pseudoligactis a corresponding increase in the production of bud energy with no change in efficiency also occurred. On the other hand, lowering of the temperature for H. pseudoligactis significantly lowered reproductive efficiency but had no effect on the total calorific output of buds. This species, in constrast to the others, appears to have a compensatory ability to adjust its efficiency to maintain a high calorific output when temperature increases. It was also found that albino Chlorohydra have budding efficiencies of around 35 percent which are not influenced by changes in food intake or light. Normal green hydras, however, have efficiencies which range from 40 to 62 percent above their albino counterparts when fed once a day and once every two days in light respectively. It it concluded first, that the symbiotic algae in the gastrodermals cells of green hydra contribute quantitatively in the order of the above amounts to the growth process in this species, and second, that green hydras have the ablity to increase their growth efficiency when food intake is reduced thus reducing the drop in calorific but output that normally occurs in the albino (control) form.     

LH responses to single doses of exogenous GnRH by social Mashona mole-rats: a continuum of socially induced infertility in the family Bathyergidae.

The Mashona mole-rat, Cryptomys darlingi, exhibits an extreme reproductive division of labour. Reproduction in the colony is restricted to a single breeding pair. The non-reproductive male and female colony members are restrained from sexual activity by being familiar and related to one another and the reproductive animals. Circulating basal concentrations of luteinizing hormone (LH) as well as LH levels measured in response to a single exogenous gonadotropin releasing hormone (GnRH) challenge are not significantly different between the reproductive and non-reproductive groups of either sex. Socially induced infertility in both non-reproductive males and females does not result from a reduced pituitary secretion of LH or decreased sensitivity to hypothalamic GnRH, but rather appears to result from an inhibition of reproductive behaviour in these obligate outbreeders. The African mole-rats exhibit a continuum of socially induced infertility with differing social species inhabiting regions of varying degrees of aridity. In this continuum a transition from a predominantly behavioural repression in a social mesic-adapted species through to complete physiological suppression lacking incest avoidance in an arid-adapted eusocial species occurs in this endemic African family of rodents.     

Energy turnover in European hares is centrally limited during early,but not during peak lactation

We investigated metabolizable energy intake (MEI) and milk energy output in European hares throughout gestation and lactation in females raising three young, i.e., close to maximum litter size in this precocial species. We hypothesized that herbivorous hares may face a central limitation of energy turnover during lactation, imposed by maximum capacity of the gastrointestinal tract. Females were provided with low-energy or high-energy diets, either continually, or during lactation only. Unexpectedly, females on either diet reached identical peak MEIs (>6 times BMR) during late lactation, with females on low-energy diet increasing food intake proportionally. Thus, we reject our hypothesis that in lactating hares, peak MEI is centrally limited. During early lactation, MEI and milk transfer was, however, significantly impaired in females on the low-energy diet, indicating a temporal central limitation due to a time-lag caused by the readjustment of energy intake capacity. Importantly, irrespective of the diet, females significantly increased peak MEI late in the breeding season. Consequently, earlier in the season, when energy reserves are still high, energy throughput was not limited by physiological constraints at all. We conclude that extreme MEI may have fitness costs, and that females maximize lifetime reproductive success by actively down-regulating MEI whenever possible.     

Variations in litter size and reproductive effort within and between some populations of Lacerta vivipara

We studied the relationships between litter size, litter weight, newborn weight, relative clutch mass and the female snout-vent length in some Lacerta vivipara populations over a period of three years.
Litter size and litter weight were positively correlated with female snout-vent length in all the populations for all the years, as in most other lizard species. Relative clutch mass generally increased with female size, though correlations appear not to be very tight.
Considering the two best studied populations suggests that montane females invest less in reproduction than lowland ones.
The main reproductive traits of the species appeared highly variable between as well as within the different populations hitherto studied.
We argue that current theory about lizard reproductive strategy requires, first to work out a good estimate of reproductive effort, and second to get more information about the relations between the species and their environmental, biotic and abiotic conditions.     

Senescence and costs of reproduction in the life history of a small precocial species

Species following a fast life history are expected to express fitness costs mainly as increased mortality, while slow‐lived species should suffer fertility costs. Because observational studies have limited power to disentangle intrinsic and extrinsic factors influencing senescence, we manipulated reproductive effort experimentally in the cavy (Cavia aperea) which produces extremely precocial young. We created two experimental groups: One was allowed continuous reproduction (CR) and the other intermittent reproduction (IR) by removing males at regular intervals. We predicted that the CR females should senesce (and die) earlier and produce either fewer and/or smaller, slower growing offspring per litter than those of the IR group. CR females had 16% more litters during three years than IR females. CR females increased mass and body condition more steeply and both remained higher until the experiment ended. Female survival showed no group difference. Reproductive senescence in litter size, litter mass, and reproductive effort (litter mass/maternal mass) began after about 600 days and was slightly stronger in CR than IR females. Litter size, litter mass, and offspring survival declined with maternal age and were influenced by seasonality. IR females decreased reproductive effort less during cold seasons and only at higher age than CR females. Nevertheless, offspring winter mortality was higher in IR females. Our results show small costs of reproduction despite high reproductive effort, suggesting that under ad libitum food conditions costs depend largely on internal regulation of allocation decisions.     

Re‐evaluating the distribution of cooperative breeding in birds: is it tightly linked with altriciality?

The evolution of cooperative breeding (CB) in birds has aroused intensive interest for decades, largely due to the paradox that some adults forgo independent breeding to help others. While much effort has been directed at understanding the adaptive significance of CB behavior, much less effort has been spent on understanding its origin. Ligon and Burt argued that the evolution of altriciality played a key role in the origin of CB since CB occurs more frequently in altricial lineages than expected if developmental mode and CB evolved independently and that both traits arose early in the avian tree of life. We mapped presence or absence of CB, and precocial or altricial development on a recent phylogeny of all birds to re‐evaluate their conclusions. Our results suggest altriciality may be more recently derived than previously thought, and that CB species clustered in a derived land bird clade (especially within Passeriformes) where we reconstructed many gains and losses. We did find a link between cooperative breeding and altriciality. However, since CB also occurs in precocial species, has not evolved in many altricial clades, and may have evolved prior to altriciality (based on some classifications of which species have CB), it is not clear whether altriciality is linked to other factors, such as benefits to group living, that are necessary for the acquisition of CB behavior, or whether altriciality may have been a driving force in the evolution of CB itself. The relative importance of these other factors versus altriciality for the origin of CB needs to be considered.     

Milk intake and energy expenditure of free-ranging northern fur seal, Callorhinus ursinus, pups

Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic investment, influences survival and growth. A number of studies have examined milk intake in otariids, but few have examined milk intake over the entire lactation period, and none has independently measured energy expenditure concurrent with milk intake. We concurrently examined milk intake, field metabolic rate (FMR), and body composition of 41 pups over the entire lactation interval in 1995 and 1996 on St. Paul Island, Alaska. One hundred two metabolic measurements were obtained with isotope dilution methods. Mean milk intake did not differ annually but increased with age and mass, ranging from 3,400+/-239 to 6,780+/-449 (+/-SE) mL per suckling bout. Milk energy consumption did not vary with age on a mass-specific basis. No differences were detected in milk volume consumed by male and female pups, either absolutely or on a mass-specific basis. Mass-specific FMR peaked during molting, was lowest postmolt, and did not vary by sex. Pups in 1995 had lower FMR than pups in 1996 and were also fatter. Mean milk energy utilized for maintenance metabolism decreased over time from 77% to 43% in 1995 and remained at 71% in 1996. Pup body mass was negatively correlated with the percentage of total body water and positively correlated with the percentage of total body lipid (TBL). Pups increased the percentage of TBL from 16% to 37%. Northern fur seal pups increased energy intake over lactation, while concurrent changes in body composition and pelage condition resulted in mass-specific metabolic savings after the molt.