Sources of variability in numbers of live births in wild golden lion tamarins (Leontopithecus rosalia)

Visually assessed body condition shows high heritability in a pedigreed great ape population

Body condition, a measure for relative fat mass, is associated with primate health, fitness, and overall welfare. Body condition is often influenced by dietary factors, age, and/or sex, but several body condition measures (body weight, weight-to-height ratios, and so on) also show high heritability across primate species, indicating a role of genetic effects. Although different measures for body condition exist, many require direct handling of animals, which is invasive, time-consuming, and expensive, making them impractical in wild and captive settings. Therefore, noninvasive visual body condition score (BCS) systems were developed for various animal species, including macaques and chimpanzees, to visually assess relative fat mass. Here we evaluate the utility of a visual BCS system in bonobos by assessing (1) inter-rater reliability, (2) links with body mass, a traditional hands-on measure of condition, and (3) the factors driving individual variation in BCS. We adapted the chimpanzee BCS system to rate 76 bonobos in 11 European zoos (92% of the adult population). Inter-rater reliability was high (s* = 0.948), BCSs were positively associated with body mass (β = 0.075) and not predicted by diet, sex, or age, nor were they associated with a higher abundance of obesity-related diseases. Instead, BCSs showed high levels of heritability (h2  = 0.637), indicating that a majority of body condition variation in bonobos is attributable to genetic similarity of the individuals. This is in line with reported h2 -values for traditional body condition measures in primates and provides support for the reliability of visual BCS systems in great apes. The results of this study emphasize an often unanticipated role of genetics in determining primate body fat and health that has implications for the management of captive primates. Application of this tool in wild populations would aid to unravel environmental from genetic drivers of body condition variation in primates.

Alloparenting by Helpers in Striped Hyena (Hyaena hyaena)

In an ongoing study of the striped hyena (Hyaena hyaena), we observed that in the nine different females, alloparenting by the daughters of a previous litter was not uncommon and occurred on fifteen different occasions, twice with two helpers. Alloparenting persisted from when the cubs are approximately a month old until they reach the age when they go out foraging with their mothers at 10-12 months. Helpers perform most maternal duties, except suckling, even in the mother's presence. Helpers accrued indirect fitness and practiced parenting before reaching sexual maturity. Future studies must study the reproductive biology of the striped hyena in the wild throughout its geographic range to elucidate additional breeding properties that have not yet been identified. The continued persecution of striped hyenas and the lack of information about their breeding rituals and capabilities in the wild mean that this study of their different reproduction strategies, focusing on surrogate mothers, is of great conservation importance. The fact that we have found cooperative breeding in this solitary species suggests that there is much more to uncover of the enigmatic striped hyena in the wild.

Timing of the luteal-placental shift is delayed with additional fetuses in litter-bearing callitrichid monkeys, Saguinus oedipus and Callithrix jacchus

The luteal-placental shift is an important milestone of mammalian pregnancy signifying when endocrine control of pregnancy shifts from the corpus luteum of the ovary to the placenta. The corpus luteum is maintained by chorionic gonadotropin (CG). Upon sufficient placental maturation, CG production wanes, the corpus luteum involutes, and control is shifted to the placenta, one consequence of which is a midgestational rise in glucocorticoid production, especially cortisol and cortisone, by both mother and fetus. Glucocorticoids are involved in initiating parturition, prenatal programming of offspring phenotype, and maturing fetal organs. Limited evidence from human pregnancy suggests that the timing of this shift is delayed in twin pregnancies, but little is known about the timing of the luteal-placental shift in litter-bearing monkeys from the primate family Callitrichidae. Here we provide evidence from cotton-top tamarins (Saguinus oedipus) and common marmosets (Callithrix jacchus) of longer duration of elevated CG associated with multiple infant births compared to single births. Urinary profiles from cotton-top tamarins demonstrate that the decline of the extended elevation of CG precedes the onset of the midpregnancy sustained rise in glucocorticoids; this shift occurs later with an increase from one to two fetuses carried to term. In the common marmoset, the onset of the sustained rise of glucocorticoids in maternal urine is also delayed with an increase in infant number. Total urinary glucocorticoid levels during the last half of gestation increase monthly but do not differ by infant number. The significant delay in the luteal-placental shift suggests a longer period of placental maturation is needed to support a greater number of fetuses.

Female Dispersion Is Necessary, but Not Sufficient, for Pairbonded Monogamy in Mammals

Explanations for the evolution of social monogamy in mammals typically emphasise one of two possibilities: females are overdispersed (such that males cannot defend access to more than one female at a time) or males provide a service to the female. However, the first claim has never been formally tested. I test it directly at three levels using population-level data from primates and ungulates. First, I show that the females of monogamous genera do not have territories that are significantly larger, either absolutely or relatively, than those of polygynous genera. Second, using two indices of territorial defendability, I show that, given their typical day journey lengths, males of most monogamous species could easily defend an area large enough to allow them to monopolise as many as 5–10 females if they ranged solitarily. Finally, I use a model of male mate searching strategies to show that the opportunity cost incurred by pairbonded males is typically 5–10 times the reproductive success they actually obtain by being obligately monogamous. This suggests that the selection pressure dissuading them from pursuing a roving male strategy must be very considerable. At present, the evidence is undecided as to whether mitigating predation or infanticide risk is the primary function, but estimates of their impacts suggest that both are in fact plausible.

Seasonal effects on testes size and sustained semen quality in captive golden-headed lion tamarins, Leontopithecus chrysomelas

The golden-headed lion tamarin (Leontopithecus chrysomelas) is an endangered primate that, according to timing of births, there seems to have seasonal reproductive patterns in captive populations inhabiting the Southern Hemisphere. The extent to which male tamarins have circannual cyclic fluctuations in testicular functions, however, remains unknown. Changes in testis size and seminal variables, therefore, were evaluated during the rainy and dry seasons of the year in seven males. There was estimation of mating and birth seasons from the breeding colony using a 27 year database (229 birth records). Births were distributed throughout the year with peaks occurring in August-October and January-March (39.7 % and 30.5 % of all births, respectively). Semen collection using penile vibrostimulation was successfully induced in more than 96 % of the attempts regardless of the season (total of 75 ejaculates). Body mass did not vary significantly between seasons, but relative testes size was larger during the dry season. Values for none of the seminal variables (total sperm count, total and progressive motility, plasma membrane and acrosome integrity, and total sperm defects), however, were different during the rainy and dry seasons. These results indicate that testicular function in golden-headed lion tamarins may not be affected by daylength changes, and that seasonal patterns of female reproduction is perhaps more relevant for the reproductive timing of the species. Furthermore, the possibility of year-round production of ejaculates containing viable sperm broadens our perspective of preserving genetic diversity within the species because there is a greater opportunity for semen collection and freezing.

Benefits of cooperation in captive Damaraland mole-rats

Although the social mole-rats are commonly classified as eusocial breeders on the grounds that groups include a single breeding female (the “queen”) and a number of nonbreeding individuals (“helpers”) of both sexes, alloparental care is not highly developed in these species and there is no direct evidence that the presence or number of nonbreeders is associated with reductions in the workload of the “queen.” An alternative interpretation of mole-rat groups is that the social mole-rats are cooperative foragers rather than cooperative or eusocial breeders. Here, in captive colonies of Damaraland mole-rats (Fukomys damarensis), we provide the first evidence that increases in the number of nonbreeding subordinates in mole-rat groups are associated with reductions in the workload of “queens” and with increases in their fecundity.

Heteropaternity of twins in ring-tailed lemurs (Lemur catta)

OBJECTIVES

This project investigated paternity among 14 sets of twins born into a colony of ring-tailed lemurs (Lemur catta) on St. Catherines Island, GA. Female L. catta commonly mate with >1 male, and twins of different sexes confirm that dizygotic twinning can occur in this species. However, no study has previously evaluated twins using genetic data to measure the proportion of mono versus dizygotic twinning in L. catta, and no study has tested for heteropaternity (sirehood by two different males) in this species. We predicted that L. catta would show a predominance of dizygosity and evidence for heteropaternity.

MATERIALS AND METHODS

Paternity was determined for 28 infants (14 sets of twins) via paternity exclusion analyses using 10 polymorphic microsatellite markers, and data were collected on sexual behavior across four mating seasons during the first cycle of mating in each year, which overlapped with the conceptive periods of these infants.

RESULTS

All twins were found to be dizygotic, as evidenced by dissimilar multilocus genotypes between the two infants of each twin pair. Heteropaternity was found in 3 of 14 (21% of) twin pairs, whereas the remaining 11 pairs of twins (79%) shared the same sire. In one case of heteropaternity, one sire was a resident male, and one sire was an extra-group male. An extra-group male also sired one of the same-sire twin pairs. All other sires of twins were group residents.

DISCUSSION

Female multiple mating, which is common to many primates including L. catta, can be viewed as an adaptive reproductive strategy whose function-in addition to fertility assurance or stimulating sperm competition-may be to increase the genetic diversity of a female's offspring, even among infants born in the same birth event. Therefore, during the course of primate evolution, the adaptive benefits of heteropaternity would be expected to have contributed to positive selection for female promiscuity.

Balancing contest competition, scramble competition, and social tolerance at feeding sites in wild common marmosets (Callithrix jacchus)

Models of primate sociality focus on the costs and benefits of group living and how factors such as rank, feeding competition, alliance formation, and cooperative behavior shape within-group social relationships. We conducted a series of controlled field experiments designed to investigate how resource distribution (one or three of four reward platforms) and amount of food on a reward platform affected foraging strategies and individual feeding success in four groups of wild common marmosets (Callithrix jacchus) living in the Caatinga of northeastern Brazil. At our field site, common marmoset groups are characterized by a single breeding female who can produce twin litters twice per year, strong social cohesion, and cooperative infant care provided principally by several adult male helpers. We found that except for the dominant breeding female, rank (based on aggression) was not a strong predictor of feeding success. Although the breeding female in each group occupied the highest rank position and obtained the greatest daily feeding success, all other group members, including adults and juveniles experienced relatively equal feeding success across most experimental conditions. This was accomplished using a balance of behavioral strategies related to contest competition, scramble competition (associated with a finder's advantage), and social tolerance (sharing the same feeding platform). Based on these results, the social structure of common marmosets is best described as "single female dominance," with the breeding female maximizing food intake needed to offset the energetic costs associated with reproductive twinning and the ability to produce two litters per year. Cooperative infant caregiving, in which the number of helpers is positively correlated with offspring survivorship, requires a set of behavioral strategies that serve to reduce contest competition and promote prosocial behaviors at feeding sites.

The common marmoset monkey: avenues for exploring the prenatal, placental, and postnatal mechanisms in developmental programming of pediatric obesity

Animal models have been critical in building evidence that the prenatal experience and intrauterine environment are capable of exerting profound and permanent effects on metabolic health through developmental programming of obesity. However, despite physiological and evolutionary similarities, nonhuman primate models are relatively rare. The common marmoset monkey ( Callithrix jacchus) is a New World monkey that has been used as a biomedical model for well more than 50 years and has recently been framed as an appropriate model for exploring early-life impacts on later health and disease. The spontaneous, multifactorial, and early-life development of obesity in the common marmoset make it a valuable research model for advancing our knowledge about the role of the prenatal and placental mechanisms involved in developmental programming of obesity. This paper provides a brief overview of obesity in the common marmoset, followed by a discussion of marmoset reproduction and placental characteristics. We then discuss the occurrence and utility of variable intrauterine environments in developmental programming in marmosets. Evidence of developmental programming of obesity will be given, and finally, we put forward future directions and innovations for including the placenta in developmental programming of obesity in the common marmoset.

Developmental origins of pregnancy loss in the adult female common marmoset monkey (Callithrix jacchus)

BACKGROUND

The impact of the intrauterine environment on the developmental programming of adult female reproductive success is still poorly understood and potentially underestimated. Litter size variation in a nonhuman primate, the common marmoset monkey (Callithrix jacchus), allows us to model the effects of varying intrauterine environments (e.g. nutrient restriction, exposure to male womb-mates) on the risk of losing fetuses in adulthood. Our previous work has characterized the fetuses of triplet pregnancies as experiencing intrauterine nutritional restriction.

METHODOLOGY/PRINCIPAL FINDINGS

We used over a decade of demographic data from the Southwest National Primate Research Center common marmoset colony. We evaluated differences between twin and triplet females in the number of pregnancies they produce and the proportion of those pregnancies that ended in fetal loss. We found that triplet females produced the same number of total offspring as twin females, but lost offspring during pregnancy at a significantly higher rate than did twins (38% vs. 13%, p = 0.02). Regardless of their own birth weight or the sex ratio of the litter the experienced as fetuses, triplet females lost more fetuses than did twins. Females with a male littermate experienced a significant increase in the proportion of stillbirths.

CONCLUSIONS/SIGNIFICANCE

These striking findings anchor pregnancy loss in the mother's own fetal environment and development, underscoring a "Womb to Womb" view of the lifecourse and the intergenerational consequences of development. This has important translational implications for understanding the large proportion of human stillbirths that are unexplained. Our findings provide strong evidence that a full understanding of mammalian life history and reproductive biology requires a developmental foundation.

Evolutionary genetics and implications of small size and twinning in callitrichine primates

New World monkeys (NWMs) are characterized by an extensive size range, with clawed NWMs (subfamily Callitrichinae, or callitrichines) such as the common marmoset manifesting diminutive size and unique reproductive adaptations. Perhaps the most notable of these adaptations is their propensity toward multiple gestations (i.e., dichorionic twins and trichorionic triplets). Indeed, with the exception of Goeldi's monkey (Callimico), callitrichine singleton pregnancies rarely occur. Multiple gestations seem to have coevolved with a suite of reproductive adaptations, including hematopoetic chimerism of siblings, suppression of reproduction in nondominant females, and cooperative alloparenting. The sequencing of the common marmoset (Callithrix jacchus) genome offers the opportunity to explore the genetic basis of these unusual traits within this primate lineage. In this study, we hypothesized that genetic changes arising during callitrichine evolution resulted in multiple ovulated ova with each cycle, and that these changes triggered adaptations that minimized complications common to multiple gestations in other primates, including humans. Callitrichine-specific nonsynonymous substitutions were identified in GDF9, BMP15, BMP4, and WFIKKN1. WFIKKN1, a multidomain protease inhibitor that binds growth factors and bone morphogenetic proteins, has nonsynonymous changes found exclusively in common marmosets and other tested callitrichine species that twin. In the one callitrichine species that does not produce twins (Callimico), this change has reverted back to the ancestral (nontwinning) primate sequence. Polymorphisms in GDF9 occur among human cohorts with a propensity for dizygotic twins, and polymorphisms in GDF9 and BMP15 are associated with twinning in sheep. We postulate that positive selection affected NWM growth patterns, with callitrichine miniaturization coevolving with a series of reproductive adaptations.

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.

Toward a nonhuman primate model of fetal programming: phenotypic plasticity of the common marmoset fetoplacental complex

Nonhuman primates offer unique opportunities as animal models in the study of developmental programming and the role of the placenta in developmental processes. All primates share fundamental similarities in life history and reproductive biology. Thus, insights gleaned from studies of nonhuman primates have a higher degree of biological salience to human biology than do studies of rodents or agricultural animals. The common marmoset monkey is a small-bodied primate from South America that produces litters of dizygotic fetuses that share a single placental mass. This natural variation allows us to model different intrauterine conditions and associated fetoplacental phenotypes. The marmoset placenta is phenotypically plastic according to litter size. Triplet litters are characterized by low individual fetal weights and significantly more efficient placentas and attendant alterations to the microscopic architecture and endocrine function, thus modeling a nutrient restricted intrauterine environment. Consistent with this model, triplet neonates experience a higher risk of perinatal mortality and an increased likelihood of elevated adult weight. Recent evidence has shown that the intrauterine experience of females has an impact on their own pregnancy outcomes in adulthood: triplet females experience significantly greater pregnancy loss than do twin females. The marmoset monkey thus represents a potential powerful nonhuman primate model of multiple pregnancies, restrictive prenatal experiences, and differential reproductive outcomes in adulthood, which may have important implications for studying the impact of in vitro fertilization on adult reproductive health. It is still too early to determine exactly what developmental pathways lead to this disparity or what specific role the placenta plays; future work on this front will be critical to establish the marmoset as an important model of fetal programming of reproductive function in adulthood and across generations.

Abundance of jackfruit (Artocarpus heterophyllus) affects group characteristics and use of space by golden-headed lion tamarins (Leontopithecus chrysomelas) in Cabruca agroforest

Cabruca is an agroforest of cacao trees shaded by native forest trees. It is the predominant vegetation type throughout eastern part of the range of the golden-headed lion tamarins, Leontopithecus chrysomelas, an endangered primate endemic to Atlantic Forest. Understanding how lion tamarins use this agroforest is a conservation priority. To address this question, we documented the diet, home range size, group sizes and composition, density, number of litters and body condition of lion tamarins living in cabruca, and other habitats. Jackfruit, Artocarpus heterophyllus, was the most used species used by lion tamarins in cabruca and was widely available and used throughout the year. In cabruca, home range size was the smallest (22-28 ha) and density of lion tamarins was the highest (1.7 ind/ha) reported for the species. Group size averaged 7.4 individuals and was not significantly different among the vegetation types. In cabruca, groups produced one or two litters a year, and all litters were twins. Adult males in cabruca were significantly heavier than males in primary forest. Our study is the first to demonstrate that breeding groups of golden-headed lion tamarins can survive and reproduce entirely within cabruca agroforest. Jackfruit proved to be a keystone resource for lion tamarins in cabruca, and bromeliads were important as an animal prey foraging microhabitat. In cases where cabruca contains concentrated resources, such as jackfruit and bromeliads, lion tamarins may not only survive and reproduce but may fare better than in other forest types, at least for body condition and reproduction.

Alloparenting experience affects future parental behavior and reproductive success in prairie voles (Microtus ochrogaster)

Various hypotheses have been proposed to explain the function of alloparental behavior in cooperatively breeding species. We examined whether alloparental experience as juveniles enhanced later parental care and reproductive success in the prairie vole (Microtus ochrogaster), a cooperatively breeding rodent. Juveniles cared for one litter of siblings (1EX), two litters of siblings (2EX) or no siblings (0EX). As adults, these individuals were mated to other 0EX, 1EX or 2EX voles, yielding seven different pair combinations, and we recorded measures of parental behaviors, reproductive success, and pup development. As juveniles, individuals caring for siblings for the first time were more alloparental; and as adults, 0EX females paired with 0EX males spent more time in the nest with their pups. Taken together, these results suggest that inexperienced animals spend more time in infant care. As parents, 1EX males spent more time licking their pups than 2EX and 0EX males. Pups with either a 1EX or 2EX parent gained weight faster than pups with 0EX parents during certain developmental periods. While inexperienced animals may spend more time in pup care, long-term benefits of alloparenting may become apparent in the display of certain, particularly important parental behaviors such as licking pups, and in faster weight gain of offspring.

Placental efficiency and intrauterine resource allocation strategies in the common marmoset pregnancy

Mothers and fetuses are expected to be in some degree of conflict over the allocation of maternal resources to fetal growth in the intrauterine environment. Variation in placental structure and function may be one way a fetus can communicate need and quality to its mother, potentially manipulating maternal investment in its favor. Whereas common marmosets typically produce twin litters, they regularly give birth to triplet litters in captivity. The addition of another fetus is a potential drain on maternal resource availability and thus a source of elevated conflict over resource allocation. Marmoset littermates share a single placental mass, so that differences in the ratio of fetal to placental weight across litter categories suggest the presence of differential intrauterine strategies of resource allocation. The fetal/placental weight ratio was calculated for 26 marmoset pregnancies, representing both twin and triplet litters, to test the hypothesis that triplet fetuses respond to intrauterine conflict by soliciting placental overgrowth as a means of accessing maternal resources. In fact, relative to fetal mass, the triplet marmoset placenta is significantly undergrown, with individual triplets associated with less placental mass than their twin counterparts, suggesting that the triplet placenta is relatively more efficient in its support of fetal growth. There still may be an important role for maternal-fetal conflict in the programming of placental structure and function. Placental adaptations that solicit potential increases of maternal investment may occur at the microscopic or metabolic level, and thus may not be reflected in the size of the placenta as a whole.

Local resource competition and local resource enhancement shape primate birth sex ratios

Sex ratio theory provides a powerful source of testable predictions about sex allocation strategies. Although studies of invertebrates generally support predictions derived from the sex ratio theory, evidence for adaptive sex ratio biasing in vertebrates remains contentious. This may be due to the fact that most studies of vertebrates have focused on facultative adjustment in relation to maternal condition, rather than processes that might produce uniform sex biases across individuals. Here, we examine the effects of local resource enhancement (LRE) and local resource competition (LRC) on birth sex ratios (BSRs). We also examine the effects of sex differences in the costs of rearing male and female offspring on BSRs. We present data from 102 primate species and show that BSRs are skewed in favour of the dispersing sex in species that do not breed cooperatively, as predicted by the LRC model. In accordance with the LRE model, BSRs are generally skewed in favour of the more beneficial sex in cooperatively breeding primate species. There is no evidence that BSRs reflect the extent of sexual size dimorphism, an indirect measure of the costs of rearing male and female offspring. These analyses suggest that adaptive processes may play an important role in the evolution of BSRs in vertebrates.

Life history costs and benefits of encephalization: a comparative test using data from long-term studies of primates in the wild

The correlation between brain size and life history has been investigated in many previous studies, and several viable explanations have been proposed. However, the results of these studies are often at odds, causing uncertainties about whether these two character complexes underwent correlated evolution. These disparities could arise from the mixture of wild and captive values in the datasets, potentially obscuring real relationships, and from differences in the methods of controlling for phylogenetic non independence of species values. This paper seeks to resolve these difficulties by (1) proposing an overarching hypothesis that encompasses many of the previously proposed hypotheses, and (2) testing the predictions of this hypothesis using rigorously compiled data and utilizing multiple methods of analysis. We hypothesize that the adaptive benefit of increased encephalization is an increase in reproductive lifespan or efficiency, which must be sufficient to outweigh the costs due to growing and maturing the larger brain. These costs and benefits are directly reflected in the length of life history stages. We tested this hypothesis on a wide range of primate species. Our results demonstrate that encephalization is significantly correlated with prolongation of all stages of developmental life history except the lactational period, and is significantly correlated with an extension of the reproductive lifespan. These results support the contention that the link between brain size and life history is caused by a balance between the costs of growing a brain and the survival benefits the brain provides. Thus, our results suggest that the evolution of prolonged life history during human evolution is caused by increased encephalization.

The adaptive value of sociality in mammalian groups

According to behavioural ecology theory, sociality evolves when the net benefits of close association with conspecifics exceed the costs. The nature and relative magnitude of the benefits and costs of sociality are expected to vary across species and habitats. When sociality is favoured, animals may form groups that range from small pair-bonded units to huge aggregations. The size and composition of social groups have diverse effects on morphology and behaviour, ranging from the extent of sexual dimorphism to brain size, and the structure of social relationships. This general argument implies that sociality has fitness consequences for individuals. However, for most mammalian species, especially long-lived animals like primates, there are sizable gaps in the chain of evidence that links sociality and social bonds to fitness outcomes. These gaps reflect the difficulty of quantifying the cumulative effects of behavioural interactions on fitness and the lack of information about the nature of social relationships among individuals in most taxa. Here, I review what is known about the reproductive consequences of sociality for mammals.

Are men really that bad as fathers? The role of men's investments

Human pair-bonding and paternal involvement have long been attributed to the need for biparental rearing of altricial offspring with extended periods of dependency. More recently, researchers have focused on the fertility benefits that pair-bonding offers men and have re-conceptualized paternal care as a stratagem designed to curry favor with the recipient children's mother. These models, however, fail to explain a number of puzzling empirical findings, namely the lack of a significant and robust effect of father-presence cross-culturally, despite what appears to be true paternal involvement. I argue that the record is better explained by conceptualizing reproduction within unions as a joint venture, in which men's contributions are not simply lumped onto women's invariant levels of parental investment, but one in which men's involvement allows wives to reduce their own allocations to parental investment and increase those to fertility (fertility model), thereby maximizing the production of the union, not simply child survivorship.

Effects of social status, age, and season on androgen and cortisol levels in wild male golden lion tamarins (Leontopithecus rosalia)

This study examines factors affecting androgen and cortisol levels in wild, male golden lion tamarins (Leontopithecus rosalia). Golden lion tamarins are a cooperatively breeding species in which groups often contain two potentially breeding males. Brothers frequently emigrate together and develop a clear dominance hierarchy, but interactions between them are primarily affiliative. Duos in which the males are not related are less stable. In addition, reproductive skew theory predicts that dominant males will be less likely to share reproduction with related subordinates. As such, we predicted that both androgens and cortisol would be higher in subordinate males unrelated to the dominant male. We also predicted that androgens in breeding males would be higher during the mating season than the birth/infant care season, as per Wingfield's "challenge hypothesis" (1990). Fecal samples were collected from 24 males in 14 social groups and assayed by enzyme immunoassay. Androgen levels were higher in breeding males during the mating season, thus supporting the challenge hypothesis. However, while subordinate males unrelated to the dominant male had significantly lower androgens than any other group, cortisol levels were not correspondingly higher. These results suggest that unrelated subordinate males show measurable reproductive suppression and may use strategies such as infantilization to avert aggression from dominant males.

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.

Maternal age, parity, and reproductive outcome in captive chimpanzees (Pan troglodytes)

As early as the 1970s, it was suggested that nonhuman primates may serve as models of human reproductive senescence. In the present study, the reproductive outcomes of 1,255 pregnancies in captive chimpanzees (Pan troglodytes) were examined in relation to parity and its covariate, maternal age. The results show that the percentage of positive pregnancy outcomes was negatively correlated with increasing parity. In addition, spontaneous abortions, stillbirths, and caesarian sections (C-sections) were positively correlated with increasing parity. Maternal age, rather than parity, was found to be the most important predictor of negative birth outcome. This study supports research demonstrating reproductive decline and termination in nonhuman primates, and is the first to quantitatively account for this phenomenon in captive female chimpanzees.

Opportunistic mothers: female marmosets (Callithrix kuhlii) reduce their investment in offspring when they have to, and when they can

All female primates incur energetic costs associated with producing and caring for offspring, but females belonging to the New World primate family Callitrichidae, the marmosets and tamarins, appear to face even further demands. In fact, the energetic demands of rearing callitrichid infants are thought to have led to the evolution of cooperative infant care in these species. If this explanation is true, then one might expect that natural selection should also have shaped patterns of maternal behavior to be sensitive to the costs of reproduction and equipped females to reduce their investment in offspring under certain conditions. Therefore, we examined the maternal effort and postpartum endocrine profiles of individual female marmosets (Callithrix kuhlii) across conditions that represented two hallmarks of callitrichid reproduction-conception during the early postpartum period and alloparental assistance. When females conceived during the early postpartum period and faced the upcoming demands of caring for their newly conceived litters (Study 1), they significantly reduced their caregiving effort and had significantly higher postpartum levels of estradiol relative to breeding attempts in which conception occurred later in the postpartum period. Postpartum estradiol was negatively correlated with maternal carrying effort. When experienced alloparents were present (Study 2), females again reduced their caregiving effort relative to breeding attempts in which experienced alloparents were not present. Postpartum cortisol, however, did not vary as a function of experienced alloparental assistance. The results of these studies suggest that female marmosets have been subjected to similar selection pressures as females of other primate taxa--to maximize their reproductive success by reducing their investment in offspring under the worst and best of conditions--and suggest that hormones may mediate within-female variation in maternal care. These studies also provide support for the notion that mothers are "flexible opportunists" when it comes to providing care to their young.

Reproductive output, maternal age, and survivorship in captive common marmoset females (Callithrix jacchus)

Common marmosets (Callithrix jacchus) demonstrate significant variation in reproductive output on both a yearly and lifetime basis in comparison to other anthropoid primates. We explore the factors that may be most important in determining reproductive variation in captive common marmosets. Studies have found that maternal age, maternal condition, and dam survivorship are related to reproductive output; however, these reports are not in agreement and are far from conclusive. With the use of a large, multicolony, demographic database pooling data across five marmoset colonies, we examined litter information for 1,649 litters, and reproductive summaries for 400 dams to assess 1) how reproductive output variation (total production, total weaned production) is determined by litter size, interbirth interval (IBI), age at first birth, and dam survival age; 2) the relationship between maternal age and reproductive output variables; and 3) relationship between the reproductive output variables and survival. We used stepwise regression procedures to describe the amount of variation in lifetime reproductive output among dams, and found that mean litter size accounted for 18% of the variance in total production, survival age accounted for 10.6%, age at first birth accounted for 8.8%, and mean IBI accounted for 5%. For total (nonzero) weaned production, survival age accounted for 7.6% of variance, age at first birth accounted for 7.2%, mean IBI accounted for 2%, and mean litter size accounted for 1.6%. We identified significant effects (P<0.05) of maternal age on litter size and IBI length, but no effect of dam age on weaned litter size. Cox proportional hazards regression analyses revealed significant effects (P<0.01) of number of litters, age at first birth, and site on dam survivorship. Dams that produced more litters showed higher survivorship. Age at first birth showed a positive relationship with dam survivorship, i.e., dams that delayed first reproduction had higher survival. Our findings about reproductive variation in marmosets may have practical applications for the management of marmoset breeding colonies.

Paternal care in the social and diurnal striped mouse (Rhabdomys pumilio): laboratory and field evidence

Paternal care is rare in mammals, occurring mainly in carnivores and neotropical primates, in which the difficulties of long generation time and large individuals lead to small sample sizes. Here, the authors show that paternal care can be easily studied in the four-striped mouse (Rhabdomys pumilio) because (a) captive males show all the patterns of parental care as do females, with the obvious exception of nursing; (b) in the field, wild males act amicably toward juveniles and retrieve pups experimentally presented to them; (c) the striped mouse facilitates experimental approaches in captivity because it has a short generation period and can be kept in large numbers; and (d) the striped mouse is diurnal, not only making observations in captivity easier but also enabling direct observations in the field.

Characteristics of reproductive biology and proximate factors regulating seasonal breeding in captive golden-headed lion tamarins (Leontopithecus chrysomelas)

Reproduction is highly demanding in terms of energy expenditure, and the costs and benefits associated with postponing or investing in a reproductive effort are crucial determinants of an individual's fitness. Understanding the reproductive potential of a species under varying ecological conditions offers important insights into the dynamics of its social system. This study provides the first detailed analysis of the reproductive potential of wild- and captive-born golden-headed lion tamarins (Leontopithecus chrysomelas) under captive conditions, based on studbook data compiled during 1984-2000. Litters produced by wild-born females breeding in captivity are similar in size to litters observed in the wild, but smaller than litters of captive-born females. The more stringent ecological conditions experienced by wild-born females during maturation may result in a lifelong effect on litter size. However, interbirth intervals are shorter for wild-born than captive-born females. The relatively smaller burden of infant care that results from having smaller litters may allow wild-born females to sustain the next pregnancy sooner. Reproduction in the Brazilian captive population is highly seasonal for both wild-born females and females born in captivity in Brazil. Changes in photoperiod over a year provide a proximate explanation for changes in the proportion of conceptions and births per month. Outside Brazil, breeding occurs year-round, and no clear birth peak is apparent. Information from field reports that could be used to relate this finding to ecological factors, such as resource availability, is unavailable.