Palatal segment contributions to midfacial growth in three inbred mouse strains.

Following facial prominence fusion, anterior-posterior (A-P) elongation of the palate is a critical aspect of palatogenesis and integrated midfacial elongation. Reciprocal epithelial-mesenchymal interactions drive secondary palate elongation and periodic signaling center formation within the rugae growth zone (RGZ). However, the relationship between RGZ dynamics and the morphogenetic behavior of underlying palatal bone mesenchymal precursors has remained enigmatic. Our results indicate that cellular activity at the RGZ simultaneously drives rugae formation and elongation of the maxillary bone primordium within the anterior secondary palate, which more than doubles in length prior to palatal shelf fusion. The first formed palatal ruga, found just posterior to the RGZ, represents a consistent morphological boundary between anterior and posterior secondary palate bone precursors, being found at the future maxillary-palatine suture. These results suggest a model where changes in RGZ-driven A-P growth of the anterior secondary palate may produce interspecies and intraspecies differences in facial prognathism and differences in the proportional contribution of palatal segment-associated bones to total palate length. An ontogenetic comparison of three inbred mouse strains indicated that while RGZ-driven growth of the anterior secondary palate is critical for early midfacial outgrowth, subtle strain-specific bony contributions to adult palate length are not present until after this initial palatal growth period. This multifaceted illustration of normal midfacial growth dynamics confirms a one-to-one relationship between palatal segments and upper jaw bones during the earliest stages of palatal growth, which may serve as the basis for evolutionary change in upper jaw morphology. Additionally, identified mouse strain-specific differences in palatal segment elongation provide a useful foundation for understanding the impact of background genetic effects on facial morphogenesis.

Influence of climatic stress on nonmetric sexually dimorphic features of the skull and pelvis.

OBJECTIVES: Human sexual dimorphism is frequently assessed through skull and pelvic size and shape. Researchers suggest that climatic variation and the associated stress may be significant factors in sexual dimorphism's etiology. However, little research has specifically investigated climatic effects on nonmetric skeletal indicators of sex. To further appreciate the plasticity of human biology, a comparative study of standard skull and pelvic nonmetric sex indicators is presented. METHODS: A Native Alaskan archeological sample (n = 104) and a component of the Terry collection (n = 99) represent populations originating from different climatic environments in recent history. These sex-balanced groups are compared through Tukey-Kramer's method and Greene's t-test to determine any variation in degree of sexual dimorphism within and between samples. RESULTS: The results reinforce the complex and multifaceted relationship between climate and sexual dimorphism. The Terry sample demonstrated a greater degree of sexual dimorphism with statistically significant differences in robusticity of the mastoid process and nuchal crest compared with the Native Alaskans. A more "male" morphotype and reduced dimorphism are appreciated in the pelves of Native Alaskans than the Terry sample. CONCLUSIONS: This research highlights a reduction in sexual dimorphism in populations under greater climatic stress and contributes to the production of more accurate skeletal assessments in future investigations. Discussion of confounding factors suggest more research is necessary to untangle climate and human morphology's complex relationship. This study contributes to a greater appreciation of human biological plasticity, ecogeographic variation, and the evolution of modern human diversity.