The sources of individual differences in human and non-human animals remain controversial. We demonstrate that diet and genetics interact in determining the ontogenetic trajectory of chemosensory and prey preferences in the common garter snake, Thamnophis sirtalis, a dietary generalist. In litters of neonate snakes from a single small field in an earthworm-ingesting population, initial responses to chemical cues from fish and worm were similar, with zero heritabilities. After 12 meals on fish, however, the heritability of both fish and worm chemosensory responses increased markedly, the change in response to fish but not worm chemicals was heritable, the relative preference for fish versus worm was heritable, and the change in relative preference was heritable. In addition, growth rates on each diet were related to changes in chemoreceptive responses. Such genetic-environment variation that emerges only after equivalent ontogenetic experience may be a factor in responses to environmental change in many species.

With relatively high fertility and short lifespan, marmoset monkeys (Callithrix jacchus) may become useful primate models of prenatal nutritional effects on birth condition and adult disease risk. The present study determined the effects of energy restriction to 75 % of expected ad libitum consumption during mid-(day 66) or late (day 99) gestation on maternal weight, fetal growth and pregnancy outcomes in this species. Mid-restriction reliably induced the loss of pregnancy before term, at 92 d, on average. Of the late-restricted pregnancies, four of seven were normal term length while three were preterm deliveries, at 101, 117 and 132 d. Control females had a mean mid-pregnancy weight gain of 0·67 g/d while mid-restricted females lost 2 0·65 g/d, on average. Control pregnancies averaged a 1·06 g/d gain during late pregnancy, while energy-restricted females lost 20·67 g/d, on average. Restriction-related weight change was highly variable, ranging from þ0·55 to 2 2·56 g/d for mid-restriction pregnancies and from þ0·79 to 2 3·91 g/d for late-restriction pregnancies. For mid-restriction pregnancies, the number of restriction days was best explained by linear weight change and total weight loss while the number of restriction days in late pregnancy was best explained by linear weight change alone. In late-restriction pregnancies, smaller females had higher daily weight losses. Restrictions did not induce litter-size reduction or growth restriction in those infants that were delivered at term but the size of aborted fetuses suggested that at least some pregnancies lost preterm may have involved impaired intra-uterine growth.

Corticotropin-releasing hormone (CRH), a potent neuropeptide, is produced by the placenta of anthropoid primates. No other mammals, including prosimian primates, are known to produce placental CRH. In humans, placental CRH appears to play an important role in the progression of pregnancy to parturition. Maternal circulating CRH begins to rise early in pregnancy and increases until parturition. Gorillas and chimpanzees share this pattern of increasing maternal CRH during pregnancy with humans. In humans, chimpanzees, and gorillas, maternal CRH and estradiol concentrations are correlated, consistent with the hypothesis that CRH is involved in the biosynthetic pathway for placental estrogen production. In contrast, in baboons, maternal circulating CRH rises precipitously early in pregnancy and then declines, though CRH is detectable until birth. This research was designed to investigate the pattern of maternal circulating CRH in the common marmoset during pregnancy. Blood samples were taken across gestation from nine subjects over 11 pregnancies, and the plasma was assayed for CRH. The pattern of maternal circulating CRH in the common marmoset was similar to that of the baboon, with a rapid rise starting at about 50 days postconception and a peak at approximately 70 days postconception. By 110 days postconception, CRH concentration had plateaued at a significantly lower value. The peak and mean values for CRH were associated with fetal number (e.g., females gestating triplets had higher values than females gestating twins). Urinary estradiol showed no association with plasma CRH concentration. Marmosets appear to differ from the great apes in this regard, and to share a pattern of maternal CRH during pregnancy with the baboon, indicating that the baboon and marmoset pattern may be ancestral. The function of the early rapid rise of CRH in baboons and marmosets, and the significance of this difference between monkeys and apes, are not known.

A seven-task behavioral test was performed on 86 common marmoset (Callithrix jacchus) infants, 24-36 h following birth. This report describes the test outcome and its relation to physical condition and survival of the infants. The percentage of infants receiving a perfect score on a given task ranged from 30.6 (rooting) to 70.6% (grasping). Heavier infants were more likely to have perfect scores for crawling (F=4.20, P=0.044) and infants with a longer knee-heel length tended to be more likely to have a perfect grasping score (F=3.63, P=0.06). While the modal score was a perfect score for most individual tasks, the modal number of total perfect scores that a given infant received was 3-4 and only 4.7% of infants received perfect scores on all seven tasks. These results suggest that this group of behavioral tasks will produce a variable response within a population of neonates. While no individual behavioral score predicted survival during week 1, the number of perfect scores across all tasks was predictive of survival outcome; infants with a higher total number of perfect scores were more likely to survive (F=6.02, P=0.018). When all combinations of tests were compared, the best predictor of survival was outcome on four of the seven tests, all related to motor skills (F=7.46, P=0.009).

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.