The ontogeny of nasalheat exchange structures in Arctic artiodactyles

Abstract

Reindeer (Rangifer tarandus) live in the Arctic and have evolved special adaptations to cope with hard environmental conditions. Nasal heat exchange (NHE), which is an efficient heat and water exchange mechanism to combat loss of energy, is well documented in adult reindeer (e.g. Blix and Johnsen (1983), Johnsen 1988). However, it is not known if this mechanism is fully developed from birth and if it has the same function in newborns as in adults. Dissections, CT-scans and histology preparations have been performed in this study in order to investigate if the structure responsible for the NHE is fully developed from birth. The study shows that the double scroll turbinate structure is present from birth. The mucosal surface area exposed to the air stream of the nasal cavity was calculated with a value of 772cm2 in juvenile reindeer (male of 52.5kg). The discovery of a closed inner “bulb” (central lumen of the turbinate scroll is not open to air flux) has been important for the calculation of the surface area in relation to an efficient NHE. The most complex part of the nasal cavity, where the surface area is largest, is in the proximal slices, and it is probably the most important part of the nasal cavity for the nasal heat exchange. As a comparison, the relative mucosal surface area exposed to the air stream was much larger in muskoxen than in reindeer, although the turbinate is less complex in muskoxen than in reindeer. The ontogeny of turbinate geometry and histology was also analysed. In reindeer calf the size of vessels (arteries and veins) was smaller than in juvenile, but the density of vessels was higher. It can be speculated that a higher density is required to ensure the proper functioning of the nasal glands and because the calves have higher metabolic rates; or could be just a size fact, the juvenile is much higher so in 1cm there are less vessels than in the calf. Finally, it was concluded that the anatomy required for efficient NHE mechanism is developed from birth.