Endocrine Correlates of Reproductive Status in Breeding and Nonbreeding Wild Female Moustached Tamarins

In callitrichid primates, reproduction is usually restricted to a single female per group. Reproductive rate is high and the occurrence of a postpartum estrus can lead to simultaneous lactation and pregnancy. In contrast, nonreproductive females often show ovarian inactivity. However, most studies on callitrichid reproductive physiology have been conducted in captivity, where conditions differ considerably from those in the wild, so that reproductive conditions may be strongly modified. Using fecal estrogen and progestogen measurements to monitor female reproductive status in 2 groups of wild moustached tamarins (Saguinus mystax), we examined 1) whether reproductive females in free-ranging groups also show postpartum estrus and 2) whether nonreproductive females demonstrate signs of ovarian activity. In both reproductive females, clear changes in the excretion pattern of progestogen and estrogen metabolites over time in combination with information on parturition dates allowed us to differentiate between pregnancy, a period of postpartum ovarian inactivity lasting for 54 and 64–82 days, and a period of ovarian activity before conception. Nonreproductive females demonstrated temporal fluctuations in hormone concentrations and absolute hormone levels that were similar to ones in the breeding females during the phase of ovarian activity. The results suggest that, in contrast to most captive female tamarins, reproductive females in wild groups of moustached tamarins do not have a postpartum estrus and that nonreproductive females show ovarian activity despite the presence of a breeding female. We therefore conclude that findings from captivity should be only carefully compared to the situation in the wild.     

Sociosexual development,pair bond formation,and mechanisms of fertility suppression in female cotton-top tamarins (Saguinus oedipus oedipus)

The effect of various social environments on sociosexual behavior was examined in six young female cotton-top tamarins (Saguinus oedipus oedipus) and in three established breeding females. Behavioral observations and hormonal samples were collected on young females while they were living with their families, when they were isolated from conspecifics, and after they were paired with an unrelated male. While living with the family, all females showed a suppression of fertility and low frequencies of sociosexual behavior. Following removal from the family, isolated females displayed an increase in rate of scent marking and an increase in hormonal levels. When young females were paired with males, they were exposed to scent secretions from their natal families, from an unfamilar family, and from a control for a total of 24 weeks. After pairing, hormonal levels increased dramatically, and ovarian cyclicity began. An increase in sociosexual behavior and elevated levels of scent marking accompanied this physiological change. Newly paired females had higher rates of affiliative behavior and scent marking than did established breeding females. However, both newly paired and established breeding males were more likely to initiate contact, grooming bouts, and social sniffing than were females. Time to first ovulation was later in females who were exposed to scent secretions from their natal families than it was in those females given a control for the first 8 weeks following pairing. No female conceived during exposure to scent secretions. However, once normal ovarian cycling had begun or a pregnancy was established, exposure to scent secretions had no effect. Thus, the social environment influences the fertility, sociosexual behavior, and pair bond formation of cotton-top tamarins. In addition, chemical stimuli found in the scent secretions produced by the natal family are most likely involved in reproductive suppression.     

Costs of breeding status in the European badger, Meles meles

Compared with other mammals, reproduction is expected to be particularly costly for European badgers ( Meles meles L.) since both the gestation and mating periods occur in the winter when the animals are inactive and feed little. This paper assesses the costs of breeding status in both male and female badgers, in terms of body condition, ectoparasite load, haematology and mortality. By the end of the lactation period (May), breeding females had suffered a marked loss in body condition, although there was no such cost associated with gestation. However, females regained the weight that they had lost by the autumn following lactation. Lactating two-year-olds experienced a higher age-specific mortality than those that did not breed, but there was no difference among older females. No costs of breeding status could be detected among males at the end of the spring mating period. However, breeding males sustained testicular activity later into the summer than non-breeders, and by the autumn they had acquired more bite wounds and become anaemic. This suggests that there was a physiological cost associated with extended testicular activity in breeding males.     

High rates of pregnancy loss by subordinates leads to high reproductive skew in wild golden lion tamarins (Leontopithecus rosalia)

Across taxa, cooperative breeding has been associated with high reproductive skew. Cooperatively breeding golden lion tamarins (Leontopithecus rosalia) were long thought to have a monogynous mating system in which reproduction was limited to a single dominant female. Subordinates with few reproductive opportunities delayed dispersal and remained in the natal group to provide alloparental care to siblings, thus allowing dominant reproductive females to meet the energetic needs associated with high rates of reproduction and successful infant rearing. The goal of this study was to re-assess monogyny in wild golden lion tamarin groups based upon pregnancy diagnoses that used non-invasive enzyme immunoassay for progesterone and cortisol, combined with weekly data on individual weight gain, bi-annual physical examinations noting pregnancy and lactation status and daily behavioral observations. We established quantitative and qualitative criteria to detect and determine the timing of pregnancies that did not result in the birth of infants. Pregnancy polygyny occurred in 83% of golden lion tamarin groups studied. The loss of 64% of subordinate pregnancies compared to only 15% by dominant females limited reproductive success mainly to dominant females, thus maintaining high reproductive skew in female golden lion tamarins. Pregnancy loss by subordinate adults did not appear to result from dominant interference in subordinate hormonal mechanisms, but more likely resulted from subordinate abandonment of newborn infants to mitigate dominant aggression.     

Endocrine Monitoring of Wild Dominant and Subordinate Female Leontopithecus rosalia

In captive callitrichid primates, female reproductive function tends to vary with social status. However, little is known about the interplay between these factors in wild groups. We report observations on normative ovarian function in dominant and subordinate female golden lion tamarins (Leontopithecus rosalia) living in wild groups. We monitored ovarian status by measuring, via enzyme immunoassay, concentrations of excreted pregnanediol glucuronide (PdG) and estrone conjugates (E₁C) in fecal samples collected noninvasively from individuals in social groups in the Poço das Antas Biological Reserve, Rio de Janeiro State, Brazil. Dominant breeding females demonstrated steroid levels similar to those previously reported for wild cotton-top tamarin females, with statistically significant rises during pregnancy. The duration of elevation of fecal steroids in breeding females was ca. 4 mo, which corresponds with estimates of gestation from captive studies. Low steroid concentrations from December to June suggest a seasonally-related period of infertility in female golden lion tamarins. Dominant and subordinate females demonstrated several differences in endocrine function. In general, younger females living in intact natal family groups showed no evidence of ovarian cyclicity. We noted endocrine profiles consistent with ovulation and subsequent pregnancy for behaviorally subordinate females living in groups with unrelated males or in which a reversal in female dominance status occurred. Results suggest that in addition to changes in female reproductive endocrinology associated with puberty, the regulation of reproduction in females in wild callitrichid groups can be sensitive to status and relatedness to breeding males.     

Feast or famine: evidence for mixed capital–income breeding strategies in Weddell seals

Evolved patterns of resource expenditure for reproduction have resulted in a life history continuum across species. A strictly capital-breeding strategy relies extensively on stored energy for reproduction, whereas income breeding uses energy acquired throughout the reproductive period. However, facultative income breeding has been shown in some classically capital-breeding animals, and was originally thought to provide a nutritional refuge for smaller females incapable of securing sufficient reserves during pre-partum foraging. We examined milk composition and milk output for the Weddell seal to determine to what degree lactation was aided by food intake, and what factors contributed to its manifestation. Milk composition was independent of maternal post-partum mass and condition, but did change over lactation. Changes were most likely in response to energetic and nutritional demands of the pup at different stages of development. During early lactation, females fasted and devoted 54.9% of total energy loss to milk production. Later in lactation 30.5% more energy was devoted to milk production and evidence suggested that larger females fed more during lactation than smaller females. It appears that Weddell seals may exhibit a flexible strategy to adjust reproductive investment to local resource levels by taking advantage of periods when prey are occasionally abundant, although it is restricted to larger females possessing the physiological capacity to dive for longer and exploit different resources during lactation. This supports the assumption that although body mass and phylogenetic history explain most of the variation in lactation patterns (20–69%), the remaining variation has likely resulted from physiological adaptations to local environmental conditions. Our study confirms that Weddell seals use a mixed capital–income breeding strategy, and that considerable intraspecific variation exists. Questions remain as to the amount of energy gain derived from the income strategy, and the consequences for pup condition and survival. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Energy intake, energy expenditure, and reproductive costs of female wild golden lion tamarins (Leontopithecus rosalia)

Callitrichid females are often described as energetically constrained. We examined the energy budgets of 10 female wild golden lion tamarins (GLTs, Leontopithecus rosalia) in an effort to understand how energy intake and expenditure might influence physical condition and therefore reproductive performance. We used focal animal sampling to record behavioral data and conducted energy analyses of foods consumed by GLTs to estimate intake and expenditure. We used two-tailed Wilcoxon signed-rank tests to compare intake in the reproductive vs. nonreproductive period and expenditure in the reproductive vs. nonreproductive period. Energy intake decreased during the reproductive period compared to the nonreproductive period. While total expenditure did not vary significantly across the two periods, females spent more time and therefore expended significantly more energy engaged in energetically inexpensive behaviors (i.e., sleeping or being stationary) during the reproductive period compared to the nonreproductive period. We suggest that reproductive female GLTs may adopt a reproductive strategy that includes high intake prior to pregnancy and lactation, and energy conservation during pregnancy and lactation.     

Birth seasonality in cotton-top tamarins (saguinus oedipus) despite constant food supply and body weight

Goldizen et al. (1988) reported that wild saddle-back tamarins (Saguinus fuscicollis, Callitrichidae) show birth seasonality that is correlated with food supply and body weight. They suggested a sequence of ultimate causality in which shortage of food leads to reduced body weight which leads to timing of weaning and lactation when resources are more abundant. Cotton-top tamarins in captivity show birth seasonality despite constant food supply and body weight. Although natural availability of fruit and insects (which are key foods for tamarins) is related to rainfall, birth seasonality and body weight in captive cotton-top tamarins are unrelated to rainfall. The most likely proximate mechanism for seasonality of births in tamarins is photo-period, given existing data on populations living in natural and artificial lighting.     

The Effect of Infant Body Mass on Carrier Travel Speed in Cotton-top Tamarins (Saguinus oedipus)

Infant carrying is common in primates and may be the second most costly activity related to reproduction, after lactation. In cooperative breeding groups of callitrichids, all group members carry and care for twin infants. Previous studies have described the costs of infant carrying in terms of body mass loss and reduced locomotor capability. However, infant carrying may also influence travel speed, an important potential cost because slower speed may handicap foraging, energetic budgets, and predator avoidance. We evaluated the impact of infant carrying on the travel speed of 27 adult and 9 subadult cotton-top tamarins (Saguinus oedipus) of both sexes in large outdoor enclosures. We compared carrier speed to speed when not carrying during the 10 weeks after nine births. Subadult tamarins, which have a lower body mass than adults do, moved faster than adults when not carrying. We found no difference between the mean speeds of subadults and adults while carrying. However, the speed of carriers decreased as infant mass increased, and the slope of this negative relationship was more pronounced in subadult carriers. For every 80 g of extra mass load (the body mass of newborn twins), adults reduced their speed by 6 % and subadults by 19 % relative to noncarrying speed. We also observed a reduction in speed while carrying two infants in adult tamarins as carrying time increased. Our results contribute to an understanding of the costs of infant carrying, and serve to emphasize the importance of cooperative breeding systems in coping with these costs.     

The reproductive tactics and activity patterns of solitary carnivores: the Iriomote cat

Felids are generally considered to be crepuscular and nocturnal in their activity, but few studies have attempted to analyze the variability of their activity patterns. We studied the daily activity of the Iriomote cat Prionailurus iriomotensis by radio-tracking on Iriomote Island, Japan. The general activity patterns of Iriomote cats showed slightly prevailing activity during dark periods of the day with particular peaks at dawn and dusk or during the early hours of the night. However, these patterns were clearly dependent on the sex and reproductive status of the cat. Peaks of cats’ activity coincided with those of their main prey. On average, the cats were active for thirteen hours per day. During the mating season, the rhythm of activity in males followed that of breeding females, but not that of non-breeding ones. Males exhibited 11% higher total daily activity and longer active bouts during the mating period than in the remainder of the year. Breeding females had additional mid-day activity peak during the nursing period, but their total time of activity per day was 16% lower than in the period of kittens’ independence. Their active bouts were shorter and more frequent during nursing than at other times. These results suggest that lactating females perform frequent movements to and from the den site to care for kittens. During the non-nursing period, females increased their activity, possibly in response to lowered prey abundance and the need of intensive foraging to recover after lactation. Seasonal and sexual variation of activity patterns in the Iriomote cats confirmed the existence of different reproductive strategies of males and females of these solitary carnivores.     

Costs of infant‐carrying in the cotton‐top tamarin (Saguinus oedipus)

Infant‐carrying behavior among callitrichids seems to be a costly activity. Costs have been related to the physical efforts of carrying the weight of very heavy infants and to the resulting reduction in foraging efficiency. However, the costs of carrying in terms of the physical consequences for carriers have not previously been assessed. In this study, we have regarded weight loss in infant carriers as a measure of costs. We studied five families of cotton‐top tamarins (Saguinus oedipus) during the first 9 weeks following the birth of infants. Captive‐breeding conditions were required so that body weight could be measured frequently. To avoid inflicting undue stress on the subject animals, we used a noninvasive method for weighing the tamarins. Differences in carrying contribution were found amongst fathers and male and female helpers, with female helpers contributing less. We have found that carrying infants in the cotton‐top tamarins is an activity that produces a weight loss. Fathers and male helpers go through a maximal body weight loss. While carrying, the tamarins also decrease food intake. However, no relationship was found between contribution to carrying and feeding time or in energetic intake during feeding observations. Thus, it seems that a direct relation doesn't exist between the observations of feeding and weight loss. Fathers increase their contribution to carrying during mothers' periovulatory periods. In this period, male helpers and especially fathers go through a maximal body weight loss. We found body weight losses of up to 11.3% in one subadult male and 9.1percnt; in a father during the fifth week. No changes occurred in food intake in fathers or other male helpers during this period. During periovulatory periods, mothers carried less frequently but did increase their food intake. They gained weight from the second week after birth onward, especially during the periovulatory period. It seems that the infant‐carrying behavior of fathers and male helpers may contribute to the improvement of the mothers' physical condition after birth and therefore may support a consecutive pregnancy. Am. J. Primatol. 48:99–111, 1999. © 1999 Wiley‐Liss, Inc.     

The effects of lactation and infant care on adult energy budgets in wild siamangs (Symphalangus syndactylus)

In mammals with biparental care of offspring, males and females may bear substantial energetic costs of reproduction. Adult strategies to reduce energetic stress include changes in activity patterns, reduced basal metabolic rates, and storage of energy prior to a reproductive attempt. I quantified patterns of behavior in five groups of wild siamangs (Symphalangus syndactylus) to detect periods of high energetic investment by adults and to examine the relationships between infant care and adult activity patterns. For females, the estimated costs of lactation peaked at around infant age 4–6 months and were low by infant age 1 year, whereas the estimated costs of infant‐carrying peaked between ages 7 and 12 months, and approached zero by age 16 months. There was a transition from primarily female to male care in the second year of life in some groups. Females spent significantly less time feeding during lactation than during the later stages of infant care, suggesting that female siamangs do not use increased food intake to offset the costs of lactation. Female feeding time was highest between infant ages 16 and 21 months, a period of relatively low female investment in the current offspring that coincided with the period of highest male investment in infant care. This suggests that male care may reduce the costs of infant care for females in the later stages of a reproductive attempt. The female energy gain resulting from male care was likely invested in somatic maintenance and future reproduction, rather than the current offspring. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Food Sharing in Lion Tamarins (<Emphasis Type="Italic">Leontopithecus chrysomelas</Emphasis>): Does Foraging Difficulty Affect Investment in Young by Breeders and Helpers?

Food sharing with immatures is an important and relatively well studied aspect of infant care in many cooperative species. A key point that has not yet been fully addressed, however, is how increasing the difficulty of obtaining food influences the willingness of breeders and helpers to provision immature offspring. We used captive golden headed lion tamarins (Leontopithecus chrysomelas) to examine how breeders and helpers differ in provisioning juvenile individuals according to the level of difficulty of obtaining food. The level of difficulty in obtaining food was varied by placing the food inside tubes that allowed access only by adults. When food acquisition became more difficult, food sharing with juveniles and breeding females increased significantly. Begging calls by breeding females and juveniles increased during the experimental condition, which probably led to increases in food sharing. Breeders and helpers did not differ in their contribution to provisioning when food was easily available, nor did they differ in their contribution when food was difficult to obtain. Breeding males in callitrichids have a prominent role in transferring food to offspring, but contrary to our expectations, they did not increase food transfer in the experimental condition. An unexpected result was the increased investment of the breeding female into her current offspring when the level of difficulty of obtaining food was higher. We suggest that breeding lion tamarin females are not as constrained by reproductive costs as breeding females of other callitrichids. Degree of reproductive skew is hypothesized as a factor affecting the contribution of breeders and helpers to offspring care in cooperative breeding mammals, though we suggest that more studies are needed to validate such a generalization.     

Impact of photoperiodic exposures during late gestation and lactation periods on the pineal and reproductive physiology of the Indian palm squirrel, Funambulus pennanti

Studies on the maternal transfer of photoperiodic information in mammals indicate that the daily photoperiod perceived by the mother during the gestation-lactation period is communicated to the fetus either through the placenta or via the milk. However, the impact of photoperiodic exposures during gestation and lactation on the maternal pineal and reproductive physiology has not been reported for any tropical rodent. The exposure of pregnant female Indian palm squirrels (Funambulus pennanti) to constant light (24 h light:0 h dark), constant dark (0 h light:24 h dark), long daylength (14 h light:10 h dark) or short daylength (10 h light:14 h dark) during early gestation (< 30 days) resulted in the resorption of pregnancy, while during late gestation (> 30 days), it did not interfere with the maintenance of pregnancy. Alterations in photoperiodic condition during late gestation and lactation altered the postpartum recovery process. Pineal gland activity, as assessed by pineal mass, protein content and plasma melatonin, was lowest during the breeding phase, but increased gradually after parturition until the next breeding phase. During gestation and lactation, constant light, long daylength and short daylength conditions were less effective, while constant dark condition had a profound effect in depressing pineal gland activity, which subsequently advanced postpartum recovery. Hence, lactating females under constant darkness prepare themselves for next mating much earlier than females under natural daylength (12 h light:12 h dark) conditions. Therefore, photoperiodic information, mediated via the pineal gland, may be important for maintaining gestation physiology as well as postpartum recovery in female rodents.     

Grooming relationships between breeding females and adult group members in cooperatively breeding moustached tamarins (Saguinus mystax)

Grooming is the most common form of affiliative behavior in primates that apart from hygienic and hedonistic benefits offers important social benefits for the performing individuals. This study examined grooming behavior in a cooperatively breeding primate species, characterized by single female breeding per group, polyandrous matings, dizygotic twinning, delayed offspring dispersal, and intensive helping behavior. In this system, breeding females profit from the presence of helpers but also helpers profit from staying in a group and assisting in infant care due to the accumulation of direct and indirect fitness benefits. We examined grooming relationships of breeding females with three classes of partners (breeding males, potentially breeding males, (sub)adult non-breeding offspring) during three reproductive phases (post-partum ovarian inactivity, ovarian activity, pregnancy) in two groups of wild moustached tamarins (Saguinus mystax). We investigated whether grooming can be used to regulate group size by either "pay-for-help" or "pay-to-stay" mechanisms. Grooming of breeding females with breeding males and non-breeding offspring was more intense and more balanced than with potentially breeding males, and most grooming occurred during the breeding females' pregnancies. Grooming was skewed toward more investment by the breeding females with breeding males during the phases of ovarian activity, and with potentially breeding males during pregnancies. Our results suggest that grooming might be a mechanism used by female moustached tamarins to induce mate association with the breeding male, and to induce certain individuals to stay in the group and help with infant care.     

Infant Carrying Behavior in Callitrichid Primates: Callithrix and Leontopithecus

Care of offspring by individuals other than the mother is ubiquitous in callitrichid primates. In spite of its widespread occurrence, however, there is considerable taxonomic variation in the timing and intensity of parental effort by breeding males and nonbreeding juvenile group members. These differences may be attributable to generic and specifies differences in the costs of reproduction for females or in ecological constraints on travel and foraging. We present data on patterns of infant carrying in social groups of two taxa of callitrichid primates (Callithrix and Leontopithecus) throughout the first 3 months of infant life. We evaluated patterns of care in small groups (two or fewer juvenile or subadult helpers) and in large groups (three or more helpers in addition to the breeding adult male and female). Group size had little effect on levels of maternal carrying effort in either marmosets or lion tamarins, and mothers ceased carrying infants by 3 months of age. Carrying efforts by fathers were significantly reduced in groups with many helpers relative to small groups. Helpers carried at consistent rates during the second and third months of infant life in Leontopithecus, while in Callithrix, carrying by helpers peaked during the second month. These results suggest that if helpers reduce energetic demands on lactating females, the mechanism by which helpers reduce these burdens is independent of maternal carrying effort.     

Demographics of the European hare (Lepus europaeus) in the Mediterranean climate zone of Australia

Demographic parameters of the European hare (Lepus europaeus) in southern Australia were investigated by dissecting hares shot by hunters during each month of the year. Gender, body weight, age, sucking, lactation, weight of the abdominal alimentary canal, weight of the left peri-renal fat body, pregnancy status, presence and counts of placental scars, litter size, and stage of gestation were recorded. From those data, growth rates, age at weaning, age and weight at puberty, date of conception, projected birth date, recruitment, survivorship, and the relationships between lactation and fat stores and alimentary capacity were determined.Fecundity of the southern Australian hares followed the seasonal pattern reported for northern hemisphere populations. However, output was lower per female and particularly per older female. Females began breeding at an earlier age such that recruitment into the southern Australian population was more dependent on females in their first year of life than on older females. Growth rates were comparable with European rates. Although high chill factors were apparently associated with higher leveret mortality, there was paradoxically higher overall mortality during the spring-early summer period of higher plant growth than in the late summer–winter period of lower plant growth and more extreme weather conditions. Fat was accumulated during pregnancy and would act as a buffer against the possibility of inadequate food availability during lactation, but hares increased the capacity of the alimentary canal during lactation and presumably with it their ability to assimilate energy to meet the demands of lactation.     

Dietary energetics of the insectivorous Mexican free-tailed bat (Tadarida brasiliensis) during pregnancy and lactation

Stomach content analysis of 20 pregnant (x body mass=13.4 g) and 18 lactating (x body mass=11.5 g) female Tadarida brasiliensis revealed that the diet, expressed as percent volume, consists largely of lepidopterans, coleopterans, hymenopterans, and dipterans, in decreasing order of importance. We found no significant difference in the diet of pregnant and lactating females when expressed as percent volume. However, when expressed as percent frequency, proportionately more pregnant females fed on lepidopterans, coleopterans, and dipterans than did lactating bats, and proportionately more lactating females fed on hymenopterans. We found no significant differences in the percentages of water, lean dry mass, fat, and energy density in the stomach contents of pregnant and lactating females. Water in stomach contents averaged 62.7% and fat and lean dry mass averaged 22.2% and 15.2%, respectively (expressed as percentage of wet mass); energy density averaged 31.2 kJ g^–1 dry mass. This relatively high energy density of stomach contents, as compared to whole insects, can be attributed to the consumption of insects high in fat (especially flying ants) and the abdomens only of moths and beetles (other body parts being discarded). Estimates of nightly food intake increased markedly from mid- to late pregnancy, stabilized or decreased during late pregnancy, and increased again during early to mid-lactation. Average nightly feeding rate doubled from pregnancy to lactation and increased threefold during the first half of lactation. By adjusting our gravimetric estimates of nightly feeding rate upwards by 40% (based on estimates of field metabolic rate), we estimate that the average nightly energy intake of female T. brasiliensis ranges from 57 kJ day^–1 in early lactation to 104 kJ day^–1 in mid-lactation. These estimates represent nightly feeding rates averaging 39% and 73% of a female's body mass in the period from early to mid-lactation, respectively.     

The tradeoff between torpor use and reproduction in little brown bats (Myotis lucifugus)

In mammals, reproduction, especially for females is energetically demanding. Therefore, during the reproductive period females could potentially adjust patterns of thermoregulation and foraging in concert to minimise the energetic constraints associated with pregnancy and lactation. We assessed the influence of pregnancy, lactation, and post-lactation on torpor use and foraging behaviour by female little brown bats, Myotis lucifugus. We measured thermoregulation by recording skin temperature and foraging by tracking bats which carried temperature-sensitive radio-tags. We found that individuals, regardless of reproductive condition, used torpor, but the patterns of torpor use varied significantly between reproductive (pregnant and lactating) females and post-lactating females. As we predicted, reproductive females entered torpor for shorter bouts than post-lactating females. Although all females used torpor frequently, pregnant females spent less time in torpor, and maintained higher skin temperatures than either lactating or post-lactating females. This result suggests that delayed offspring development which has been associated with torpor use during pregnancy, may pose a higher risk to an individual’s reproductive success than reduced milk production during lactation. Conversely, foraging behaviour of radio-tagged bats did not vary with reproductive condition, suggesting that even short, shallow bouts of torpor produce substantial energy savings, likely obviating the need to spend more time foraging. Our data clearly show that torpor use and reproduction are not mutually exclusive and that torpor use (no matter how short or shallow) is an important means of balancing the costs of reproduction for M. lucifugus.     

Age-specific survival and reproductive performances in fur seals: evidence of senescence and individual quality

Life history theory hypothesises that breeding events induce reproductive costs that may vary among individuals. However, the growing number of studies addressing this question are taxonomically biased, therefore impeding the generalisation of this hypothesis, especially with regard to marine top predators. This study investigated age‐related survival and breeding performances in subantarctic fur seal (Arctocephalus tropicalis) females from Amsterdam Island, southern Indian Ocean. Using multistate capture–recapture models on data obtained from known‐age tagged females over eight consecutive years, we tested for evidence of senescence, individual quality, and reproductive costs in terms of future survival and fecundity. Adult female yearly survival appeared high and constant throughout time. While a two age‐class model was preferred in non‐breeders, breeding females exhibited three age classes with a maximum survival for the prime‐age class (7–12 years). Survival and reproductive probabilities decreased from 13 years onward, suggesting senescence in this population. Survival was lower for non‐breeders than for breeders, among both prime‐aged (0.938 vs 0.982) and older (0.676 vs 0.855) females. Furthermore, non‐breeders exhibited higher probabilities of being non‐breeders the following year than did breeders (0.555 vs 0.414). Such results suggest consistency in female breeding performance over years, supporting the hypothesis that non‐breeding tend to occur among lower quality individuals rather than representing an alternative strategy to enhance residual reproductive value. However, the high proportion of females that did not breed during two consecutive years, and the lower probability of being a successful breeder after a greater reproductive effort confirmed the existence of reproductive costs, especially during the second half of the lactation. These results also suggest that younger age‐classes included a higher proportion of lower quality individuals, which are likely to face higher costs of reproduction. Such hypotheses lead to consider the first breeding event as a filter generating a within‐cohort selection process in females.