A Comparison of the Utility of Craniometric and Dental Morphological Data for Assessing Biodistance and Sex-Differential Migration in the Pacific Islands

Genetic analyses of mitochondrial DNA and Y-chromosome sequences yield contrasting pictures of the movement of peoples into the Pacific Islands, with mtDNA suggesting rapid migration and a lack of admixture with indigenous Melanesian populations, and the Y-chromosome data maintaining a higher level of admixture due to a slower rate of migration. A possible explanation for this discrepancy is the matrilocal residency pattern practiced by early Pacific settlers, in which Melanesian men were brought into settler communities to intermarry with local women. If matrilocal residency was practiced, male populations will exhibit higher within-groups variance and lower between-group variance than female populations. This occurs when males are immigrating to into their subpopulation, and are therefore less likely to be related to other males, while females remain in the group of their birth and are more likely to be related to other females in their subpopulation.

Biological distance, or biodistance, is a measure of the relatedness among human groups separated temporally or geographically in order to reconstruct population history, assess ancestry, or elucidate social organization. Studies in biodistance rely on morphological variation of heritable physical traits as a proxy for variation in the underlying genetics for these traits. Two common sources of data for biodistance studies included craniometric measurements of the cranium and scores of morphological variants in crown and root formation of dentition. These two types of data vary in several important ways. Cranial measurements are metric and continuous, while dental morphological scores are binary, non-metric, and discontinuous. Additionally, cranial size and shape are highly sexually dimorphic in humans and are influenced by environmental stressors during life, while dental traits do not exhibit sexual dimorphism and are highly canalized. Compared to cranial measurements, dental morphology should more directly reflect the underlying genotype influencing phenotypic expression, and thus lend itself more appropriately to studies of biodistance in human populations.

This research analyzes dental non-metric scores and craniometric measurements for five Pacific Island populations to assess inter- and intra-population variances in order to elucidate post-marital residence pattern and compare general sex-differential routes of gene flow. Additionally, these two types of data and separately-measured datasets are compared to evaluate their consensus as lines of evidence in studies of biodistance and social organization for these particular populations. Mean Measure of Divergence and Mahalanobis generalized distance are applied to the dental and craniometric data, respectively, to quantify biological distance among the populations in question, are modelled via principal coordinates analysis, and are compared via Mantel tests and Generalized Procrustes Analysis to quantify their concordance. The variance of the more mobile sex will be greater within-groups and less between-groups compared to the less mobile sex based on these distance measures, indicating whether these populations generally practiced a matrilocal or patrilocal post-marital residence pattern. If dental traits are a more direct indicator of underlying genetic variation than craniometric measurements, the concordance of their respective distance matrices will be not be significant.