Genetic and environmental impacts on litter size and early infant survival in three species of callitrichids.

Callitrichids are unusual among anthropoid primates in that they can deliver one to four offspring per litter in captivity. Factors underlying intraspecific variation in litter size are unclear. Data from the Oak Ridge Associated Universities (ORAU) Marmoset Research Center provided an opportunity to investigate determinants of variation in (1) average litter size at birth and (2) average litter size surviving to 2 weeks of age in Saguinus fuscicollis, S. oedipus, and Callithrix jacchus. The objectives were to (1) investigate the impact of parity, husbandry, origin (wild or captive), and subspecific hybridization on phenotypic variance in litter size and (2) to estimate the heritability of litter size at birth and at 14 days. Husbandry changes were the only significant covariate and increased litter size at birth in C. jacchus only. Heritability estimates for average litter size at birth were significant only in S. fuscicollis (h2 = 0.306). Heritability of average litter size at 2 weeks of age was not significantly greater than zero. Estimates of genetic variability were relatively high, however both traits had very high levels of residual variance. The results suggest that litter size is a malleable trait that may respond to environmental factors.