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New World monkeys offer important insight into the evolutionary bases of size variation in higher primates. This reflects the fact that among several platyrrhine lineages, closely related taxa are characterized by marked differences in adult body weight. In the case of tamarins, for example, adult body weight ranges from 350 gms in Saguinus fuscicollis to 570 gms in Saguinus mystax. However, little is known regarding the ontogeny of size and shape variation within the genus Saguinus. In this study, we evaluate the hypothesis that, among tamarins, ontogenetic scaling, or shifts along a shared relative growth trajectory, account for size and shape variation. Specifically, we focus on comparisons of limb segment length among smaller-and larger-bodied tamarin species, and examine evidence for age and sexbased differences in growth.
Somatometrics representing S. fuscicollis, S. geoffroyi, S. labiatus, and S. mystax were analyzed. These species are represented by 250 wild-trapped, tranquilized, weighed, measured, and released individuals from Panama, Peru, and Brazil. Animals examined ranged in age from infant to adult. Allometric analyses of twelve variables describing limb and body proportions were conducted using reduced major axis regression.
Our results indicate that, in general, ontogenetic scaling accounted for size differences among tamarin species. Thus, S. fuscicollis followed relative growth trajectories comparable to those of larger tamarin species, but followed these to smaller size ranges. However, there also was evidence for shape differences between species. Specifically, arm span in S. fuscicollis exceeded values for all other tamarin species, indicating relatively long forelimbs across a range of sizes during ontogeny. This is consistent with differences in patterns of positional behavior and feeding ecology that characterize S. fuscicollis. Evidence of sex-based differences in tamarin growth trajectories also is discussed.
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