Genetic integration of molar cusp size variation in baboons

Abstract

Many studies of primate diversity and evolution rely on dental morphology for insight into diet, behavior, and phylogenetic relationships. Consequently, variation in molar cusp size has increasingly become a phenotype of interest. In 2007 we published a quantitative genetic analysis of mandibular molar cusp size variation in baboons. Those results provided more questions than answers, as the pattern of genetic integration did not fit predictions from odontogenesis. To follow up, we expanded our study to include data from the maxillary molar cusps. Here we report on these later analyses, as well as inter-arch comparisons with the mandibular data. We analyzed variation in two-dimensional maxillary molar cusp size using data collected from a captive pedigreed breeding colony of baboons, Papio hamadryas, housed at the Southwest National Primate Research Center. These analyses show that variation in maxillary molar cusp size is heritable and sexually dimorphic. We also estimated additive genetic correlations between cusps on the same crown, homologous cusps along the tooth row, and maxillary and mandibular cusps. The pattern for maxillary molars yields genetic correlations of one between the paracone-metacone and protocone-hypocone. Bivariate analyses of cuspal homologues on adjacent teeth yield correlations that are high or not significantly different from one. Between dental arcades, the non-occluding cusps consistently yield high genetic correlations, especially the metaconid-paracone and metaconid-metacone. This pattern of genetic correlation does not immediately accord with the pattern of development and/or calcification, however these results do follow predictions that can be made from the evolutionary history of the tribosphenic molar.

Geometric morphometric 3D shape analysis and covariation of human mandibular and maxillary first molars

“…PC2 described a shearing of the buccal cusps in relation to the lingual cusps in the mesiodistal direction. These modes of variability suggest that cusps may be more tightly integrated in the mesiodistal than in the buccolingual direction, a finding that agrees with the different functional characteristics of the buccal and lingual cusps (Molnar and Gantt, 1977;Molnar and Ward, 1977;Renaud et al, 2009;Koh et al, 2010;Gomez-Robles and Polly, 2012).…”

Elucidating the evolution of hominid dentition in the age of phenomics, modularity, and quantitative genetics

“…Our goal has been to describe/partition phenotypic variation such that it better reflects the underlying genetic architecture. We find that genetic correlations between seemingly homologous features often cross individual teeth and the dental arcades, but can be genetically independent on the same crown (such as the orientation of the molar lophs/lophids, Hlusko et al, 2004b, and molar cusp areas, , Koh et al, 2010. Tooth linear dimensions have significant genetic correlation on the same crown, but their patterns of genetic interrelatedness with body size are distinct.…”

“…We have elucidated shared genetic effects across a plethora of dental phenotypes (Grieco et al, 2013;Hlusko and Mahaney, 2003Hlusko et al, 2004aHlusko et al, ,b, 2006Hlusko et al, , 2011Koh et al, 2010). Whereas most of the previous work cited above searched for additive genetic effects on the variance of one phenotype, our research on baboon dental variation focused on and explored genetic correlations between various ways to measure the phenotype.…”

Modularity of the anthropoid dentition: Implications for the evolution of the hominin canine honing complex

“…As a result, estimates of G in primates have been limited to a few laboratory populations (e.g., Papio sp. at the Southwest National Primate Research Center [SNPRC]) (e.g., Hlusko and Mahaney, 2007a,b, 2009Koh et al, 2010. Due to limitations in the estimation of G, the phenotypic variance-covariance matrix (P-matrix or P) is often used to estimate G in non-pedigreed samples (Cheverud, 1988a).…”