What's in a tooth? : signals of ecogeography and phylogeny in the dentition of macaques (Cercopithecidae: Macaca)

The aim of the present work was to investigate the impact of the varying environmental conditions on the taxonomic and phenotypic diversification of a geographically widespread and ecologically successful Old World primate genus, the macaques (Cercopithecidae: Macaca). To this end, the relationship between geography, ecology, phylogeny, and phenotypic variation among macaques was investigated. Constraints to phenotypic variation – and thus evolution – were also analysed in the form of observed amounts of phenotypic variation and patterns of phenotypic integration. A total of 72 standard linear measurements of teeth and associated cranial and mandibular structures were taken for a total sample of 744 specimens from 13 species of macaques. Climate and ecological data were collated from the literature. Univariate and multivariate statistics were employed for the analysis. Patterns of variation, covariation, and allometry were analysed in the dentition, both within and between species. The ecogeographical analysis was carried out by means of two-block partial least squares and a type of multivariate regression, both in a phylogenetic framework. Phylogenetic signal was tested for by means of Blomberg’s K. Macaque teeth differ in their variability. All teeth covary with each other, although correlations are strongest within tooth classes. Size was a strong contributing factor to dental integration, as evinced by lower correlations between teeth once allometric effects were removed. Integration patterns also showed modularity between the anterior and the posterior dentition. Between-species variation in overall craniodental size was associated with temperature, latitude, and body size. Species also varied, albeit to a lesser degree, along an antero-posterior contrast in relative tooth size. Larger anterior were found to be associated with frugivory and tropical ecology, whereas a larger posterior dentition was linked to a more folivorous diet and temperate environments. The latter pattern was largely a function of phylogenetic relatedness. Phylogenetic signal was generally strong in the dentition, although it was substantially greater in the anterior teeth (incisors and canines) than in the posterior teeth (premolars and molars). Macaques show adaptive differentiation in body size in response to temperature along a latitudinal cline, corroborating the presence of the Bergmann effect in macaques. There was no conclusive support for further adaptive differentiation, despite an association between relative tooth size and diet. Allometry appears to channel evolutionary divergence of macaques along a line of least evolutionary resistance, and developmental modularity allows for partly uncoupled evolution of the anterior and posterior dentition. Future research should be aimed at broadening the taxonomic scope to include craniodental variation of the African papionins and cercopithecins in order to put the observed macaque patterns in a broader evolutionary context.