ABSTRACT: Close associations between adult males and lactating females and their dependent infants are not commonly described in non-monogamous
mammals. However, such associations [sometimes called “friendships” (Smuts 1985)] are regularly observed in several primate species in which females mate with multiple males during the fertile period.
The absence of mating exclusivity among “friends” suggests that males should invest little in infant care, raising questions
about the adaptive significance of friendship bonds. Using data from genetic paternity analyses, patterns of behavior, and
long-term demographic and reproductive records, we evaluated the extent to which friendships in four multi-male, multi-female
yellow baboon (Papio cynocephalus) groups in Amboseli, Kenya represent joint parental care of offspring or male mating effort. We found evidence that mothers
and infants benefited directly from friendships; friendships provided mother–infant dyads protection from harassment from
other adult and immature females. In addition, nearly half of all male friends were the genetic fathers of offspring and had
been observed mating with mothers during the days of most likely conception for those offspring. In contrast, nearly all friends
who were not fathers were also not observed to consort with the mother during the days of most likely conception, suggesting
that friendships between mothers and non-fathers did not result from paternity confusion. Finally, we found no evidence that
prior friendship increased a male’s chances of mating with a female in future reproductive cycles. Our results suggest that,
for many male–female pairs at Amboseli, friendships represented a form of biparental care of offspring. Males in the remaining
friendship dyads may be trading protection of infants in exchange for some resources or services not yet identified. Our study
is the first to find evidence that female primates gain social benefits from their early associations with adult males.
Behavioral Ecology and Sociobiology 04/2012; 63(9):1331-1344. · 3.18 Impact Factor
ABSTRACT: An impressive body of research has focused on the mechanisms by which the steroid estrogens (E), progestins (P), and glucocorticoids (GC) ensure successful pregnancy. With the advance of non-invasive techniques to measure steroids in urine and feces, steroid hormones are routinely monitored to detect pregnancy in wild mammalian species, but hormone data on fetal loss have been sparse. Here, we examine fecal steroid hormones from five groups of wild yellow baboons (Papio cynocephalus) in the Amboseli basin of Kenya to compare the hormones of successful pregnancies to those ending in fetal loss or stillbirth. Using a combination of longitudinal and cross-sectional data, we analyzed three steroid hormones (E, P, GC) and related metabolites from 5 years of fecal samples across 188 pregnancies. Our results document the course of steroid hormone concentrations across successful baboon pregnancy in the wild and demonstrate that fecal estrogens predicted impending fetal loss starting 2 months before the externally observed loss. By also considering an additional 450 pregnancies for which we did not have hormonal data, we determined that the probability for fetal loss for Amboseli baboons was 13.9%, and that fetal mortality occurred throughout gestation (91 losses occurred in 656 pregnancies; rates were the same for pregnancies with and without hormonal data). These results demonstrate that our longstanding method for early detection of pregnancies based on observation of external indicators closely matches hormonal identification of pregnancy in wild baboons.
Hormones and Behavior 06/2006; 49(5):688-99. · 3.87 Impact Factor
ABSTRACT: Steroid concentrations during late pregnancy and early lactation may be affected by both a female's reproductive history and her current condition, and may in turn predict subsequent life-history events, such as offspring survival. This study investigated these relationships in a wild primate population through the use of fecal steroid analysis in repeated sampling of peripartum baboons (Papio cynocephalus). Fecal samples were collected from 32 females in five groups within the Amboseli basin during 8 weeks prior to parturition and 13 weeks postpartum. From December 1999 through February 2002, 176 fecal samples were collected from individuals representing 39 peripartum periods. Fecal concentrations of progestins (fP), estrogen metabolites (fE), glucocorticoids (fGC), and testosterone metabolites (fT) were measured by radioimmunoassay. Steroid concentrations declined from late pregnancy to lactation, and the decline was greatest and most precipitous for fE and fP. Primiparous females had significantly higher mean fE concentrations in each of the last 2 months of pregnancy compared to multiparous females. Among multiparous females, fE and fT were significantly higher during late pregnancy in females carrying a male fetus compared to those carrying a female fetus. During early lactation, high fT in young mothers predicted subsequent infant death during the first year of life. These findings illustrate the potential power of repeated fecal-steroid sampling to elucidate mechanisms of life-history variability in natural populations. They also document significant differences in hormone profiles among subgroups, and highlight that such normative subgroup information is essential for interpreting individual variability in hormone-behavior associations.
American Journal of Primatology 10/2004; 64(1):95-106. · 2.22 Impact Factor
ABSTRACT: Maternal care is the most significant measure of successful adaptation among female mammals. Understanding the predictors of individual differences in offspring care is a major objective of mammalian reproductive biology. Recent studies suggest that differences in caregiving motivation may be associated with variation in glucocorticoid (GC) hormones in new mothers. Despite these intriguing reports, questions remain about the stability of this association during a period of rapid change in both behaviour and physiology, about whether this relationship is dependent on other nonhormonal variables and about the generality of this pattern across species and in wild populations. Glucocorticoids modulate animals' responses to ongoing stressors and may also prepare animals for predictable future challenges. We evaluated evidence for both actions of GCs on maternal responsiveness towards infant cries during the first 2 months of infancy in 34 wild baboon mother–infant dyads in Amboseli, Kenya. We found that stable individual differences in faecal GCs during late pregnancy predicted stable individual differences in maternal responsiveness after birth, even after controlling for maternal rank and parity, and infant sex and distress rate. This study is among the first to provide evidence of preparative actions of GCs in wild animals and to show stability of behavioural and hormonal traits during a period of rapid changes in both hormones and behaviour. Because elevations in GCs during late pregnancy are probably primarily of fetal rather than maternal origin, our results raise the intriguing possibility that parent–offspring conflict may underlie the preparative actions of GCs on maternal responsiveness to infant distress.