Assessing Ecogeographical Variation in the Nasal Passages Utilizing 3D Semilandmarks

Prior research has shown strong statistical relationships between geographically-patterned variation in nasal skeletal morphology and global climatic conditions. Specifically, the nasal skeletons of individuals indigenous to cold-dry environments tend to be longer, taller, and especially narrower, than those from hot-humid environments. As the nasal passages heat and humidify inspired air for entry into the lungs, this morphological patterning is believed to reflect the specific air-conditioning demands of different climates. However, while it is widely assumed the morphology of the nasal skeleton accurately reflects that of the functional (soft-tissue) nasal passages, the existence of ecogeographic variation in the three-dimensional (3D) nasal soft tissues has yet to be empirically demonstrated. This study investigates 3D shape variation in decongested soft-tissue nasal passages of individuals ancestrally derived from cold-dry (CD) and hot-humid (HH) environments (n=20). Using 3D Slicer and Avizo, a total of 260 semilandmarks were collected from the decongested nasal passages of Each individual. General Procrustes Analysis (GPA) was then used to align the semilandmark configurations of all 20 individuals and a Principal Component Analysis (PCA) was subsequently performed using the Geomorph package in R. Our results indicate PC1 (19.13%) largely contrasts CD individuals with positive PC1 scores (relatively narrower nasal passages) from HH individuals with negative PC1 scores (relatively wider nasal passages). These results generally conform to morphological expectations, suggesting a general concordance between skeletal and decongested soft-tissue nasal anatomy. This study thus provides the impetus for future research investigating the relationship between ecogeographic variation in nasal soft-tissue anatomy and air-conditioning physiology.