Study of the evolution of tooth and body size in callitrichid primates

This study, conducted by Anna M. Hardin, investigates the genetic architecture of dental dimensions in the brown-mantled tamarin (Saguinus fuscicollis) to illuminate how genetic correlations among dental traits relate to body size evolution in callitrichid primates.

The primary objectives were to describe genetic correlations between linear dental measurements and derived dental size metrics, assess whether tamarin dentition exhibits genetic modularity by tooth type, and consider how body size reduction in the callitrichine lineage might relate to the genetic patterning of dental traits. To address these questions, Hardin analyzed data from 302 individuals with access to a larger pedigree of 386 individuals. Quantitative genetic analyses were performed using maximum likelihood variance decomposition in SOLAR to estimate genetic correlations for linear dental measurements, estimated crown areas, and measures of relative premolar and molar size. The results indicate strong genetic integration across the dentition of brown-mantled tamarins, with little evidence for modularity by tooth type either within or between the maxilla and mandible. Variables expected to show genetic patterning based on prior work in other primate taxa were not consistently heritable in this population: the relative molar size variable hypothesized to be genetically patterned in baboons was not significantly heritable in these tamarins, and relative premolar size did not meet criteria for being considered genetically patterned in this sample.

These findings demonstrate that the pattern of genetic correlations among dental dimensions can vary across primate lineages and provide evidence for evolutionary change in the genetic architecture of the dentition in the callitrichine lineage. Hardin discusses how pervasive genetic integration without tooth-type modularity is likely to constrain dental evolution in ways that modularity would not, and how reductions in body size associated with callitrichine evolution may have played a role in shaping genetic covariance among dental traits.

The study underscores the value of quantitative genetic analyses for revealing variation in the genetic architecture underlying primate dental morphology and calls for additional analyses across more primate populations to build broader comparative evidence. By combining pedigree-based genetic modeling with comprehensive dental measurements in a well-documented tamarin population, the work clarifies the relationship between genetic integration, trait modularity, and potential evolutionary constraints on dental morphology, situating the results within broader questions about how shifts in body size and lineage-specific histories influence the evolvability of complex morphological systems in primates.