Behaviorally Induced Change in Post-cranial (Upper Ankle Joint) Morphology: Phenotypic Plasticity in an Altered Habitat

Abstract

The interplay of behavior and radical habitat change and its effect on skeletal morphology is examined among Macaca populations using Generalized Procrustes, Relative Warps, and Singular Warp analyses of the Talo-crural (upper ankle) joint. Forty-six osteological specimens of matched tali and tibiae from three species of Macaca formed the study group (7 M. thibetana, 10 M. fascicularis and 29 M. mulatta) with documented provenience and generational data for captive specimens. Four subgroups of M. mulatta were compared: wild shot (5), captive populations in caged (5) or open facilities (7), and a multigenerational free-ranging facility (12). The Null Hypotheses: No significant difference in shape was tested using singular warp analysis. All three species differed in shape, a result consistent with prior studies, their genetics and habitats. Among M. mulatta subgroups only the multigenerational free-ranging subgroup was significantly different. Wild shot, caged and open facility specimens clustered at the negative, flexible pole of the singular warp vector, while free-ranging multigenerational specimens clustering at the positive pole with talo-crural shape more stable. Behavioral change over multiple generations may result in alteration in post-cranial shape (talo-crural joint shape) when habitat radically changes, phenotypic plasticity an important mechanism.