Bădescu et al. (2016) Alloparenting is associated with reduced maternal lactation effort and faster weaning in wild chimpanzees (original) (raw)
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Royal Society open science, 2016
Alloparenting, when individuals other than the mother assist with infant care, can vary between and within populations and has potential fitness costs and benefits for individuals involved. We investigated the effects of alloparenting on the speed with which infants were weaned, a potential component of maternal fitness because of how it can affect inter-birth intervals, in wild chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Uganda. We also provide, to our knowledge, the first description of alloparenting in this population and present a novel measure of the contribution of milk to infant diets through faecal stable nitrogen isotopes (δ(15)N). Using 42 mother-infant pairs, we tested associations of two alloparenting dimensions, natal attraction (interest in infants) and infant handling (holding, carrying), to the proportion of time mothers spent feeding and to maternal lactation effort (mean nursing rates and mother-infant δ(15)N differences). Neither natal attraction nor in...
Maternal lactational investment is higher for sons in chimpanzees
Behavioral Ecology and Sociobiology, 2022
Maternal lactational investment can affect female reproductive rates and offspring survival in mammals and can be biased towards infants of one sex. We compared estimates of lactation effort among mothers, assessed as their potential milk contribution to age-specific infant diets (mother-infant differences in fecal stable nitrogen isotopes, δ15N), to the timing of weaning (infant age at last nursing bout) and to maternal inter-birth interval lengths for male and female infant chimpanzees (Pan troglodytes) at Ngogo, Uganda. Infant males had greater proportions of milk in their age-specific diets, indicated by higher mother-infant differences in δ15N (Generalized Estimating Equation, GEE: p
The energetics of lactation and the return to fecundity in wild chimpanzees
Behavioral Ecology, 2012
xpected to compromise future offspring production. This trade-off is particularly salient for mammals in which mothers bear the exclusive burden of lactation and draw from their own energy reserves to provision offspring. The degree to which lactation impacts future reproductive ability should vary not only by the absolute cost of milk production but also by the ability of individual mothers to afford it. Few studies have been able to quantify the costs of lactation or how they affect reproductive rates. Here, we examine the metabolic load of lactation in chimpanzees, a species with intensive parental investment and extremely slow reproductive rates. We used urinary C-peptide of insulin to trace changes in energetic condition in 17 wild, unprovisioned chimpanzee mothers in Kibale National Park, Uganda. C-peptide levels of nursing mothers were depressed for six months postpartum, thereafter showing a net increase through the second year. These changes are consistent with milestones of infant physical and behavioral development. Mothers inhabiting lower quality foraging areas experienced a higher metabolic load of lactation, as indicated by lower C-peptide profiles than mothers in food-rich areas. Ovarian activity was closely correlated with energetic condition. Cycling resumed only after a sustained period of energy gain, suggesting that the slow reproductive pattern in wild chimpanzees results not only from the direct expense of milk production but also from the long period that mothers require to recover their physical condition in a food-limited environment.
American Journal of Physical Anthropology, 2018
Objectives: Infanticide by males is common in mammals. According to the sexual selection hypothesis, the risk is inversely related to infant age because the older the infant, the less infan- ticide can shorten lactational amenorrhea; risk is also predicted to increase when an infanticidal male's chance of siring the replacement infant is high. Infanticide occurs in chimpanzees (Pan troglodytes), a species in which male dominance rank predicts paternity skew. Infanticidal male chimpanzees (if low-ranking) are unlikely to kill their own offspring, whereas those who are cur- rently rising in rank, particularly when this rise is dramatic, have an increased likelihood of fathering potential future infants relative to any existing ones. Given that mothers should behave in ways that reduce infanticide risk, we predicted that female chimpanzees, and specifi- cally those with younger, more vulnerable infants, would attempt to adjust the exposure of their infants to potentially infanticidal males. Specifically, mothers of young infants should reduce their association with adult males in general, and to a greater extent, with both low-ranking males and those rising in rank from a position where paternity of current infants was unlikely, to a rank where the probability of siring the next infant is significantly higher. We also investigated the alternative possibility that rather than avoiding all adult males, mothers would increase asso- ciation with males of stable high rank on the basis that such males could offer protection against infanticide. Materials and methods: We examined data on female association patterns collected from the Budongo Forest, Uganda, during a period encompassing both relative stability in the male hierar- chy and a period of instability with a mid-ranking male rising rapidly in rank. Results: Using linear mixed models, we found that mothers reduced their association with the rank-rising male, contingent on infant age, during the period of instability. We also found evi- dence that females preferentially associated with a potential protector male during the high-risk period. Discussion: Our results support the sexually selected hypothesis for infanticide and demon- strate that female chimpanzees are sensitive to the relative risks posed by adult males.
Reproductive ecology of female chimpanzees
American journal of primatology, 2013
An important adaptive problem for mammals in general, and primates in particular, is how females can manage the high costs of reproduction in the face of fluctuating energetic supplies. For many species, the best solution is to breed seasonally such that high costs are temporally coincident with predictable periods of resource abundance. This is an unreliable strategy for some primates, such as chimpanzees (Pan troglodytes), for which large body size forces an increase in dietary complexity and prolonged reproductive efforts. Here, I review data on reproductive function in chimpanzees, a species that demonstrates a risk-averse reproductive strategy wherein reproductive investment is allocated in accordance with maternal condition. Life history parameters for chimpanzees indicate that most females produce very few surviving offspring. However, comparisons between captive and wild populations and within wild populations illustrate that variation in resource access leads to highly variable reproductive success. Focused hormonal studies have demonstrated these effects at a proximate level, with energetic influences on female dispersal, receptivity, cycle quality, conception success, and lactational amenorrhea. Downstream of these effects, female reproductive function affects sexual attractiveness, and by virtue of males’ own optimal reproductive strategies, can lead to coercive aggression and decreased foraging efficiency. Because of their extreme reproductive costs, female chimpanzees utilize a highly conservative reproductive strategy, one that minimizes the costs of ecological variation but makes them vulnerable to sexual conflict and costs of sociality. Am. J. Primatol. 75:222-237, 2013. © 2012 Wiley Periodicals, Inc.
Offspring provisioning is one of the most energetically demanding aspects of reproduction for female mammals. Variation in lactation length and weaning strategies between chimpanzees (Pan troglodytes), our closest living relative, and modern human societies have been reported. When and why these changes occurred is frequently debated. Our study used stable nitrogen isotope data of tooth root dentine from wild Western chimpanzees (Pan troglodytes verus) in Ta€ ı National Park, Côte d'Ivoire, to quantify weaning in these chimpanzees and explore if infant sex plays a role in maternal investment. We analyzed serial sections of deciduous lateral incisor root dentine from four Ta€ ı chimpanzees to establish the d 15 N signal of nursing infants; we then analyzed serial sections of first permanent mandibular molar root dentine from 12 Ta€ ı chimpanzees to provide quantitative d 15 N data on weaning in this population. Up to 2 years of age both sexes exhibited dentine d 15 N values 2-3& higher than adult female Ta€ ı chimpanzees, consistent with a nursing signal. Thereafter a steady decrease in d 15 N values consistent with the onset, and progression, of weaning, was visible. Sex differences were also evident, where male d 15 N values decreased at a significantly slower rate compared to females. Confirmation of sex differences in maternal investment among Ta€ ı chimpanzees, demonstrates the viability of using isotope analysis to investigate weaning in non-human primates. Additionally, assuming that behaviors observed in the Ta€ ı chimpanzees are illustrative of the ancestral pattern, our results provide a platform to enable the trajectory of weaning in human evolution to be further explored. Am J Phys Anthropol 153:635-642,
Building Babies, 2013
Maternal condition and maternal investment during lactation in mantled howler monkeys
American journal of physical anthropology, 2018
Lactation is a costly reproductive state for females, as it may entail decreased body condition, increased morbidity, and increased mortality risk. To offset these costs, mothers should allocate investment in infant care as a function of their physical condition. Here, we assessed the relationship between maternal condition and maternal investment in wild mantled howler monkeys (Alouatta palliata) to determine: (1) whether maternal physical condition varied as a function of food availability, activity levels and feeding effort throughout lactation; (2) whether maternal investment was affected by maternal condition and offspring age. We studied six adult females while rearing their immature offspring. We determined weekly food availability, C-peptide levels (as a measure of energy balance) in urine samples (306 samples), mothers' time budgets, feeding rates, time spent vigilant, and time spent carrying their offspring (for two years; 600 observation hours). C-peptide levels were ...
American Journal of Primatology
Weaning is a transition in early development with major implications for infant survival and well-being, and for maternal lifetime reproductive success. The particular strategy a primate mother adopts in rearing her offspring represents a negotiation between her ability to invest and her need to invest, and can be considered adaptive and influenced by biological and social factors. Any investigation into how and why maternal weaning strategies differ among non-human primates is limited by the precision of the measurement tool used to assess infants’ weaning ages. Stable carbon and nitrogen isotope analysis of soft tissues (e.g., hair, nails, feces, urine, blood) offers an objective means of monitoring the weaning status of infants. In this study, we assess stable isotope ratios in blood serum from 14 captive rhesus macaque dyads (Macaca mulatta) at infant ages 2, 5, 6, 7, 8, and 10 months to estimate the timing of weaning events. Male infants wean earlier than female infants. Infants with the lowest birth weights wean latest. Most infants wean upon reaching 2.5 times their birth weights, sooner than when weaning elsewhere has been predicted for captive cercopithecine primates. The longest weaning periods (ca. 10 months) are observed among infants of small mothers. The shortest weaning period, between 2 and 5 months, was among the lowest ranking dyad. Parity andmothers’ ages had no discernible effect on the timing of weaning events. The stable carbon and nitrogen isotope values of dams during lactation are significantly different than those of a nonlactating adult female outgroup, raising questions about the suitability and selection of adult comparative baselines in studies where lactating mothers cannot be sampled longitudinally (e.g., bioarchaeology; paleontology). Am. J. Primatol.