Ultrastructure of the parotid gland in two species of naked-backed bats

Abstract

Naked-backed bats of the genus Pteronotus (family Mormoopidae) occur in the Neotropics from Mexico through northern South America. These are relatively small-sized insectivorous species that frequently roost in caves. Eight specimens of naked-backed bats (Pteronotus parnellii) were live-trapped in Suriname and one in Cuba (P. quadridens). Their parotid glands were fixed in an aldehyde mixture designed for field work and postfixed in the laboratory with osmium tetroxide. Tissues were further prepared for electron microscopy by conventional means. The parotid glands of the two species of Pteronotus closely resemble each other except for the substructure of their serous secretory granules. Serous granules in P. parnellii are bizonal, with a moderately dense inner matrix and an outer, denser corona or crescent. The matrix is occupied by laminae, flakes, and filaments in random array. In contrast, serous granules in P. quadridens consist of a uniform matrix that contains dense, usually stacked toroids or tubules either in random array or packed in bundles. A parotid gland from one specimen of P. parnellii contained an endpiece that consisted of cells that contained giant (up to 9 pm in diameter) serous granules. Serous cells in both species contain aggregates of small, uniformly dense, rod-like, membrane-delimited organelles as well as occasional bundles of cytofilaments. The endpieces are separated from intercalated ducts by a ring of granulated cells that contain secretory granules that often have a bull's-eye configuration. Intercalated and striated ducts are typical in appearance, except that many of the cells in the latter contain small, dense secretory granules in their apical cytoplasm. The parotid glands in the two species of naked-baked bats differ slightly in terms of acinar secretory granule ultrastructure, but otherwise are fairly conservative. It is thought that the glands in these particular bats might represent the "basal" condition of the salivary glands of insectivorous bats and thus can serve as a reference point for making comparisons to the highly diversified (in terms of diet) phyllostomid bats.