Comparative Histology and Histochemistry of the Parotid Gland and Mandibular Gland in the Lowland Tapir (Tapirus terrestris Perissodactyla) and Aardvark (Orycteropus afer Tubulidentata)

SIMPLE SUMMARY: The goal of this study was to perform a comparative analysis of the microstructure and secretion of the parotid and mandibular glands of adult female lowland tapir and aardvark. Histological and histochemical analyses showed that while the parotid gland of the lowland tapir consists of numerous large lobes of different shapes, those of the aardvark were smaller and more ovoid in shape. The parotid gland lobes were of different sizes (small, medium, and large) and shapes in the tapir, while all were roughly ovoid in shape in the aardvark. The obtained results showed that the mandibular gland secretion had a mucoserous character in aardvark, while in lowland tapir, the dominance of mucous secretion was determined. These differences could be related to the specific diets of these two different species. ABSTRACT: In terrestrial mammals, the parotid and mandibular glands secrete different types of saliva into the oral cavity. Both glands were obtained from two female lowland tapirs (Tapirus terrestris) and one female aardvark (Orycteropus afer) from the Wroclaw Zoological Garden (Poland) and examined by light microscopy (hematoxylin and eosin, mucicarmine, periodic acid-Schiff, Alcian blue pH 1.0, Alcian blue pH 2.5, Alcian blue pH 2.5/PAS, and Hale’s dialysed iron). Both the parotid glands observed in the lowland tapir and aardvark were compound alveolar serous secretory units, and in both species, the secretion was composed of neutral and acidic mucopolysaccharides (sialo and sulfated mucins). However, in both the lowland tapir and aardvark, a histological examination found the stroma of the mandibular gland was divided into very large lobes by poorly marked connective tissue. While many interlobar and striated ducts were found in the aardvark, very few were found in the lowland tapir. The mandibular gland was a branched tubular (mucous secretion) type in the lowland tapir, but it was a branched tubuloalveolar (mucous-serous) type in the aardvark. In all tested glands, the secretion was composed of neutral mucopolysaccharides, acid-sulfated mucosubstances, and sialomucins.