The design and the role of the nasal passages in temperature regulation in the dik-dik antelope (Rhynchotragus kirkii) with observations on the carotid rete.

Exhaled air temperatures (Tex) and rectal temperatures (Trec) were measured in five dik-dik antelopes under controlled environmental temperatures (Ta) between 15 and 40 degrees C. In addition morphometric analysis of the nasal passages, gross and histological identification of the carotid rete were carried out in an attempt to illustrate a possible brain cooling system in this small ungulate. Below Ta of 30 degrees C, Tex decreased with decreasing Ta leading to the establishment of a temperature gradient of about 20 degrees C between Ta and Trec at a Ta of around 15 degrees C. At Ta of 30 degrees C Tex was approximately half a degree lower than the Trec. Gross and histological studies revealed the presence of carotid rete and profuse vascularisation of the nasal turbinates. Morphometric analysis established a mean volume density of the nasal passages (np) in the splanchnocranium (sp) (VV(np,sp], surface density (SV(np,sp] and harmonic mean width of the nasal passages (W) of 9.5%, 2.15 cm2/cm3 and 1.23 mm, respectively. Combined physiological and anatomical measurements suggest that the dik-dik may possess an efficient brain cooling and water conserving system. The design of the upper respiratory system in these antelopes may help these animals to tolerate the extremes of temperatures and insolation encountered in their habitat.