Meeting Abstract
Respiratory turbinates – maxillo- and nasoturbinal bones in the nasal cavity of mammals – have been proposed as anatomic correlates of endothermy in mammals. By substantially augmenting the epithelial surface area of the nasal cavity, respiratory turbinates help and reduce heat and water loss in expired air. Respiratory turbinate surface area (RTSA) has been shown to be a strong predictor of field metabolic rate (FMR) in mammals, seemingly in support of the endothermy hypothesis. An alternative hypothesis, however, proposes that respiratory turbinates evolved in mammalian ancestors in response to falling atmospheric oxygen level in the Late Triassic. If the latter is true, we would predict that RTSA is higher in contemporary mammals adapted to high-altitude hypoxia. Deer mice (Peromyscus maniculatus) from lowland and highland populations were maintained in laboratory conditions under normobaric normoxia and hypobaric hypoxia, respectively. Following ventilatory and respiratory measurements in the whole animal, the nasal cavities (n=5) were analysed histologically. RTSA correlated with body mass (17-26g), but did not differ between treatment groups. RTSA did not show a significant correlation with breathing rate, tidal volume, or minute ventilation. Further, RTSA was not a good predictor of metabolic or water loss rates. This suggests that RTSA does not match intraspecific variation in respiratory parameters in a rodent species with the widest altitudinal distribution among North American mammals. As such, our results do not lend support to the hypothesis that respiratory turbinates evolved in response to a bout of global hypoxia over 200 million years ago. Whether other factors may have played a role in sculpting the intranasal morphology of mammals is yet to be determined.
