Limb growth in captive Galago senegalensis: getting in shape to be an adult

Abstract

Since primate infants are not simply miniature adults, adult shape results from differential growth patterns of individual body segments. Initially an infant relies on its mother for transportation, and later begins independent locomotion. Skeletal growth patterns must meet the functional demands of independent locomotion. In this study we sought to determine whether Galago senegalensis braccatus follow the general primate pattern of decreasing intermembral index (IMI) throughout ontogeny. We also asked whether ontogenetic attainment of adult limb proportions coincides with attainment of independent locomotion, i.e., do infants reach adult limb proportions near the time they begin independent locomotion (approximately 7 weeks of age)? Mixed-longitudinal data were taken from a sample of 10 captive-born Galago senegalensis. Linear lengths of the trunk, arm, forearm, thigh, and leg were measured in the animals from birth until they were approximately 500 days old. The IMI and the ratio of each limb segment to both trunk length and the cube root of body mass were calculated. The results of a Mann-Whitney Wilcoxon rank-sum test for unmatched samples indicate that G. senegalensis do exhibit the primate pattern of decreasing IMI throughout ontogeny, and that the IMIs of infants at the time of initial locomotor independence are significantly higher than those of adult IMIs. Some (but not all) measures of relative limb lengths differed between neonates or 7-week-old infants and adults. Therefore, the hypothesis that infants acquire adult limb proportions by the time they begin independent locomotion is not supported by this study. The current results indicate that ontogenetic shape changes in galagos are a complex process and apparently cannot be explained by simple initial locomotor competency.