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1. Quantitative genetic analyses of postcanine morphological crown variation

   https://doi.org/10.1002/ajpa.23778  

   Stojanowski, Christopher_M ; Paul, Kathleen_S ; Seidel, Andrew_C ; Duncan, William_N ; Guatelli‐Steinberg, Debbie ( February 2019 , American Journal of Physical Anthropology)

   This article presents estimates of narrow‐sense heritability and bivariate genetic correlation for 14 tooth crown morphological variants scored on permanent premolars, first molars, and second molars. The objective is to inform data collection and analytical practices in dental biodistance and to provide insights on the development of molar crowns as integrated structures.

   African American dental casts from the Menegaz‐Bock collection were recorded for the Arizona State University Dental Anthropology System. Estimates of narrow‐sense heritability and genetic correlation were generated using SOLAR v.8.1.1, which included assessment of age, sex, and birth year as covariates. Both continuous scale and dichotomized estimates are provided.

   Heritability estimates were nonsignificant for the majority of variables; however, for variables yielding significant estimates, values were moderate to high in magnitude and comparable to previous studies. Comparing left and right‐side heritability estimates suggests directional asymmetry in the expression of environmental variance, something not seen in anterior tooth traits. Genetic correlations were moderate among antimeres and metameres and low for different traits scored on the same tooth crown. Although several negative correlations were noted, few reached statistical significance. Results affirm some of the current data cleaning and analytical practices in dental biodistance, but others are called into question. These include the pooling of males and females and combining left and right‐side data into a single dataset.

   In comparison to anterior tooth crown traits, postcanine heritabilities were more often non‐significant; however, those traits with significant heritability also tended to produce higher estimates. Genetic correlations were unremarkable, in part, because they were underpowered. However, M1 results may provide insight into the complex relationship between genes, environment, and development in determining ultimate crown form.

    

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2. Heterogeneous frailty and the expression of linear enamel hypoplasia in a genealogical population

   https://doi.org/10.1002/ajpa.24288  

   Lawrence, Julie ; Stojanowski, Christopher M. ; Paul, Kathleen S. ; Seidel, Andrew C. ; Guatelli‐Steinberg, Debbie ( April 2021 , American Journal of Physical Anthropology)

   Linear enamel hypoplasia (LEH) is a common skeletal marker of physiological stress (e.g., malnutrition or illness) that is studied within and across populations, without reference to familial risk. We examine LEH prevalence in a population with known genealogical relationships to determine the potential influence of genetic heritability and shared environment.

   LEH data of 239 individuals from a single population were recorded from the Ohio State University Menegaz‐Bock collection dental casts. All individuals were of known age, sex, and genealogy. Narrow‐sense heritability estimates were obtained for LEH presence and count data from all unworn, fully erupted teeth (excluding third molars) using SOLAR (v.8.1.1). Age, sex, and age–sex interaction were included as covariates. Models were re‐run with a household effect variable.

   LEH persists across generations in this study population with moderate, significant heritability estimates for presence in four teeth, and count in four teeth (three teeth were significant for both). When a household effect variable was added, no residual heritability remained for LEH count on any tooth. There was no significant household effect for three of the four teeth that had significant heritability estimates for LEH presence. Age was a significant covariate. Further analyses with birth year data revealed a secular trend toward less LEH.

   This study provides evidence for familial risk of LEH (genetic and environmental) that has consequences for the broad use of this skeletal marker of stress. These results have repercussions for archaeological assemblages, or population health studies, where genetic relatives and household groups might be heavily represented.

    

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3. Sex and ancestry patterning of residual correlations in human dental development: Cooperative genetic interaction and phenotypic plasticity

   https://doi.org/10.1002/ajpa.24908  

   Sgheiza, Valerie ( February 2024 , American Journal of Biological Anthropology)

   Most research in human dental age estimation has focused on point estimates of age, and most research on dental development theories has focused on morphology or eruption. Correlations between developing teeth using ordinal staging have received less attention. The effect of demographic variables on these correlations is unknown. I tested the effect of reference sample demographic variables on the residual correlation matrix using the lens of cooperative genetic interaction (CGI).

   The sample consisted of Moorrees et al.,Journal of Dental Research, 1963, 42, 1490–1502, scores of left mandibular permanent teeth from panoramic radiographs of 880 London children 3–22.99 years of age stratified by year of age, sex, and Bangladeshi or European ancestry. A multivariate cumulative probit model was fit to each sex/ancestry group (n = 220), each sex or ancestry (n = 440), and all individuals (n = 880). Residual correlation matrices from nine reference sample configurations were compared using Bartlett's tests of between‐sample difference matrices against the identity matrix, hierarchical cluster analysis, and dendrogram cophenetic correlations.

   Bartlett's test results were inconclusive. Cluster analysis showed clustering by tooth class, position within class, and developmental timing. Clustering patterns and dendrogram correlations showed similarity by sex but not ancestry.

   Expectations of CGI were supported for developmental staging. This supports using CGI as a model for explaining patterns of variation within the dentition. Sex was found to produce consistent patterns of dental correlations, whereas ancestry did not. Clustering by timing of development supports phenotypic plasticity in the dentition and suggests shared environment over genetic ancestry to explain population differences.

    

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4. Genetic correlations in the dental dimensions of Saguinus fuscicollis

   https://doi.org/10.1002/ajpa.23861  

   Hardin, Anna_M ( May 2019 , American Journal of Physical Anthropology)

   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.

   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.

   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.

   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.

    

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5. Genetic contributions to dental dimensions in brown‐mantled tamarins ( Saguinus fuscicollis ) and rhesus macaques ( Macaca mulatta )

   https://doi.org/10.1002/ajpa.23744  

   Hardin, Anna_M ( December 2018 , American Journal of Physical Anthropology)

   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).

   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.

   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.

   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.

    

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