Hand specialization, sympatry, and mixed-species associations in callitrichines

Abstract

Hand morphology in callitrichines (i.e., tamarins, marmosets, and Goeldi's monkey) is correlated with positional and foraging behaviors. This study examines hand shape in callitrichines using an allometric approach. It addresses a series of questions relating hand anatomy, insect foraging behavior, and resource partitioning in callitrichines. The main questions are: 1. Do the hands ofLeontopithecusdiffer in shape from all other callitrichine taxa allowing it to perform highly manipulative prey foraging behaviors? 2. Are the hands ofSaguinus fuscicollisadapted to manipulative foraging, and are they functionally similar toLeontopithecus’ hands? 3. Is hand morphology inS. fuscicollismore similar to the hand morphology of sympatric tamarin species with whom it does not form mixed species troops (S. nigricollisandS. tripartitus) than to those sympatric tamarin species with whom it does form mixed troops (S. mystax, S. labiatus, andS. imperator)? Measurements of hand length (HL), width (HW), and thickness (HT) were taken from 1350 museum specimens of callitrichines (Callithrix, Cebuella, Leontopithecus, Saguinus, andCallimico), squirrel monkeys (Saimiri), and owl monkeys (Aotus). The analysis indicates that hand shape covaries with foraging strategy. Specifically, the hands ofLeontopithecusare adapted for manipulative foraging and are relatively longer and more slender than the hands of other callitrichines. A similar pattern is observed in the hands ofS. fuscicollis, S. tripartitusandS. nigricollis. These latter species, however, differ significantly in shape from all other tamarin species. Large differences in hand morphology are observed among tamarin species that form mixed-species troops. These anatomical differences may permit resource partitioning and coexistence among these closely related taxa. Hand shape, expressed as log HLGM (logged hand length divided by the geometric mean of all measurements), is a good predictor of manipulative and non-manipulative prey foraging techniques employed by callitrichines.