Publications

OBJECTIVES: The objectives of this study are to describe genetic correlations between dental dimensions in a platyrrhine primate, to assess whether the brown-mantled tamarin dentition exhibits genetic modularity by tooth type, and to discuss the relationship between body size reduction and the genetic architecture of dental traits.

MATERIALS AND METHODS: Genetic correlations were estimated for linear dental measurements, estimated crown areas, and measures of relative premolar and molar size from 302 individuals, using a pedigree of 386 individuals, with maximum likelihood variance decomposition in SOLAR.

RESULTS: Genetic correlation estimates indicate strong genetic integration in the dentition of brown-mantled tamarins, with little evidence of modularity by tooth type, within and between the maxilla and mandible. The relative molar size variable hypothesized to be genetically patterned in baboons is not significantly heritable, and relative premolar size does not meet the criteria to be considered genetically patterned in this population.

DISCUSSION: These results demonstrate variation in the pattern of genetic correlations between dental dimensions in primates, providing evidence of evolution of the genetic architecture in the callitrichine lineage. Genetic integration of dental dimensions without modularity by tooth type, as demonstrated here, is expected to constrain dental evolution in ways that modularity would not. The role of body size reduction in the callitrichine lineage in the evolution of the genetic architecture of the dentition is discussed. Quantitative genetic analyses of dental dimensions in more primate populations will provide greater evidence of variation and evolution in the genetic architecture underlying primate dental morphology.

OBJECTIVES: The use of dental metrics in phylogenetic reconstructions of fossil primates assumes variation in tooth size is highly heritable. Quantitative genetic studies in humans and baboons have estimated high heritabilities for dental traits, providing a preliminary view of the variability of dental trait heritability in nonhuman primate species. To expand upon this view, the heritabilities and evolvabilities of linear dental dimensions are estimated in brown-mantled tamarins (Saguinus fuscicollis) and rhesus macaques (Macaca mulatta).

MATERIALS AND METHODS: Quantitative genetic analyses were performed on linear dental dimensions collected from 302 brown-mantled tamarins and 364 rhesus macaques. Heritabilities were estimated in SOLAR using pedigrees from each population, and evolvabilities were calculated manually.

RESULTS: Tamarin heritability estimates range from 0.19 to 0.99, and 25 of 26 tamarin estimates are significantly different from zero. Macaque heritability estimates range from 0.08 to 1.00, and 25 out of 28 estimates are significantly different from zero.

DISCUSSION: Dental dimensions are highly heritable in captive brown-mantled tamarins and free-ranging rhesus macaques. The range of heritability estimates in these populations is broadly similar to those of baboons and humans. Evolvability tends to increase with heritability, although evolvability is high relative to heritability in some dimensions. Estimating evolvability helps to contextualize differences in heritability, and the observed relationship between evolvability and heritability in dental dimensions requires further investigation.

Physical anthropologists often use nonmetric dental traits to trace the movement of human populations, but similar analysis of the teeth of nonhuman primates or the deciduous teeth is rare. Because nonmetric dental characteristics are manifestations of genetic differences among groups, they vary among geographically distant members of the same species and subspecies. We use 28 nonmetric dental traits in the deciduous molars to compare genetically and geographically distinct groups of extant African apes (Gorilla and Pan). Previous researchers have studied these traits in the adult or juvenile teeth of great apes and humans, and we score our observations according to established standards for hominins. We observe marked differences in trait frequencies between Gorilla and Pan, Pan troglodytes and P. paniscus, and two P. troglodytes subspecies but we find no significant differences between geographically isolated groups within the subspecies. Trait frequencies differ from those found in previous studies that contained fewer individuals. We find that the deciduous molars show similar variation to adult premolars and molars within Pan and Gorilla. This suggests that the deciduous dentition of these and other apes may contain diagnostic traits that are not currently in use.