Suzette D. Tardif

Effects of Allocare-Givers on Fitness of Infants and Parents in Callitrichid Primates

The effects of callitrichid primate helpers (allocare-givers other than an infant’s father) on the survival, reproduction or behavior of infants and parents are reviewed, using both published studies and data from free-ranging golden lion tamarins (Leontopithecus rosalia). Three lines of evidence suggest that helpers may increase their own inclusive fitness: (1) The number of adult males acting as helpers in free-ranging groups is correlated with the number of surviving infants in 3 callitrichid species. However, the lack of a negative correlation with number of infants dying suggests that activities other than direct infant care (e.g. territory defense) may be more important, especially in newly formed groups. (2) In 2 species, captive groups with helpers carry infants for longer periods of time than do groups without helpers. Whether such differences would translate into meaningful survival differences in free-ranging groups is unclear. (3) Helpers reduce the energetic burden of parents by reducing the amount of time they spend transporting or provisioning infants in at least 4 species. Reproductive males are more likely than reproductive females to benefit from the presence of helpers, reducing their investment in infant care activities as the number of helpers in the group increases. In free-ranging golden lion tamarins, the reproductive tenure of males, but not females, increases with the number of helpers in the group, suggesting that a reduction in energetic investment may translate into increased survival. ‘Decisions’ made by helpers to participate in infant transport are weighed against competing needs for foraging, vigilance, territory defense and, in some cases, prospecting for breeding opportunities. Given this complexity, a sophisticated model may be required to answer the question of how helpers ‘decide’ to participate in infant care versus other activities.

Lactation, maternal behavior and infant growth in common marmoset monkeys (Callithrix jacchus): effects of maternal size and litter size

Abstract. We examined the relationship between lactation performance and infant growth in a captive population of common marmosets (Callithrix jacchus) that varied in both maternal and litter size. Though common marmosets display a typical primate pattern of dilute milk and relatively slow infant growth rates (factors associated with low daily lactation investment and minimal maternal size effects), we hypothesized that the marmosets small body size would make lactation investment more sensitive to maternal size than is true for larger-bodied primates. Smaller mothers rearing twins had lower milk fat, lower gross energy in milk samples collected in mid to late lactation and lower nursing-bout frequencies than did large mothers nursing twins. Lactation performance and maternal behavior did not differ between large and small mothers when rearing singletons, with a single exception: small mothers had a lower gross energy in mid-lactation milk samples. Relative growth rates in twins but not singletons were affected by maternal size, such that small mothers supported more growth per infant when rearing singletons while large mothers supported more growth per infant when rearing twins. Among the larger mothers, only, older mothers supported somewhat, though not significantly, less growth per infant, regardless of litter size. Twin infants of small mothers appeared to respond to below-optimal levels of milk yield by initiating maternal carrying less often. The relative energy intake of mothers was similar regardless of litter or maternal size. Small mothers rearing twins drew more heavily on reserves, reflected in a linear weight loss during lactation; however, the reserves drawn upon were inadequate to meet the lactation demand, resulting in lower milk energy output. In addition, small mothers rearing twins were more likely to be ill and less likely to be fertile in the year following lactation than were large mothers of twins or mothers of any size rearing singletons.

Number of ovulations in the marmoset monkey (Callithrix jacchus): Relation to body weight, age and repeatability

The relation between number of ovulations and body weight, age or maternal identity was examined in 69 ovarian cycles from 29 captive‐born common marmoset monkeys (Callithrix jacchus). Specifically, we addressed the following questions: was there high repeatability of ovulation number? Most of the variation in ovulation number was within, rather than between subjects. Repeatability in number of ovulations was 0.081 (n = 20 females with 2–6 ovulatory cycles per female); was age related to number of ovulations? There was no relation between age and number of ovulations, either within or between subjects; and was weight related to number of ovulations? Weight was related to number of ovulations. When the relation between number of ovulations (1–2 versus 3–4) and weight was examined through a logistic regression, there was a significant relation. Also, of the 11 subjects which had a variable number of ovulations across cycles, 90.9% were heavier when ovulating 3–4 than when ovulating 2. These results are discussed as the basis for the proposal that callitrichid primates may have been selected for potential variation in reproductive output and that this variation may be related to energy availability. Am. J. Primatol. 42:323–329, 1997.

ESTIMATION OF GESTATIONAL AGES IN THE COMMON MARMOSET (CALLITHRIX JACCHUS)FROM PUBLISHED PRENATAL GROWTH CURVES

This report compares estimated gestational ages from published cubic spline curves to gestational ages estimated retrospectively from delivery dates in 28 pregnancies from ten common marmosets (Callithrix jacchus). Both CRL‐ and BPD‐based estimates of gestational age were closely correlated with delivery‐based gestational age estimates. Of the three ultrasound machines used, the one with 16 shades of gray and a sequential linear array overestimated gestational age during early pregnancy, based on CRL measures. Measures from the other two machines (64 or 264 shades of gray; linear sector and annular array or electronic phase array) were similar and resulted in a correlation of the two estimates of gestational age of 0.94 and a mean difference between the two estimates of 0.16 days with 80% of CRL‐based gestational age estimates being within ± 5 days of the delivery‐based estimate. The reliability of BPD‐based estimates of gestational age was strongly related to pregnancy outcome. BPD‐based estimates underestimated gestational age in poor outcome pregnancies (i.e., those in which infants died within 7 days of birth) but not in good outcome pregnancies. The combined CRL‐ and BPD‐based estimates on poor outcome pregnancies suggest that there was less growth in BPD in late gestation for those pregnancies that resulted in nonviable offspring. For good outcome pregnancies, the correlation between BPD‐based and delivery‐based estimates of gestational age was 0.871 and the mean difference between the two estimates was −0.06 days with 83.3% of BPD‐based estimates falling within ± 5 days of delivery‐based estimates.

Ingestion of calcium solutions by common marmosets (Callithrix jacchus)

Callithrix jacchus, the common marmoset, is a small New World primate that feeds on insects, fruit, and gum, and has a high reproductive rate for a primate. Insects are generally a poor source of dietary calcium, while gums may contain significant levels of calcium. Their high reproductive rate also suggests that reproductive female C. jacchus might be susceptible to calcium deficiency. Thus, we hypothesized that common marmosets might find solutions containing calcium to be palatable. We used choice experiments to examine this phenomenon in 14 male and 19 female common marmosets. Animals were presented with identical water bottles containing either deionized water or a calcium lactate solution (either 2% or 4% calcium lactate by weight) and intake was measured. Serum 25‐OH‐vitamin D was monitored in a subset of the animals in the experiment to examine the role of vitamin D in this behavior. Our results demonstrated that C. jacchus can distinguish between plain water and a calcium lactate solution, and that in general they prefer calcium solutions. Although animals with marginal vitamin D status did have strong preferences for calcium solutions, they did not ingest significantly more of the calcium solutions than animals that were vitamin D‐replete. Nulliparous females and males did not differ in the amounts of calcium solutions ingested. Lactating females ingested the greatest volume of the calcium solutions. Am. J. Primatol. 47:255–261, 1999.

Interactions between infant growth and survival: Evidence for selection on age‐specific body weight in captive common marmosets (Callithrix jacchus)

The objective of this study is to investigate factors influencing infant survival in captive common marmosets. We investigated the influence of age‐specific weight, litter size, caging, and the presence of helpers on survival to 6 months of age in 189 Callithrix jacchus infants. Infant survival was analyzed using Cox Proportional Hazards regression, and fitness functions were plotted to explore the relationship between survival and growth. Results indicate that weights at birth and 120 days significantly affect future survival probability. Litter size significantly influences survival prior to 60 days of age with larger litters having poorer survival. Males and females did not have significantly different survival and the presence of helpers in the group did not influence survival probability. Patterns of survival with respect to age‐specific weights suggest stabilizing selection on birth weight and directional selection on weight at 120 days of age. Am. J. Primatol. 42:269–280, 1997.