Anal glands of the Florida manatee, Trichechus manatus latirostris: A potential source of chemosensory signal expression

Abstract

In all vertebrate species examined, anal glands have been observed. These glands can be found anywhere along the anal canal and are generally a combination of apocrine and sebaceous adenomeres. They are used for signal expression in both terrestrial and aquatic settings. The goal of this study was to determine the morphology of the anal glands in the Florida manatee, Trichechus manatus latirostris, and suggest functional hypotheses through comparison to other species. Samples were collected from manatees of varying ages, during all seasons, and from both sexes (six females and five males). The glands were examined grossly and microscopically. They are present in fetal, juvenile, and adult male and female manatees and are found in clusters on each side of the anal canal within the sphincter muscles. Unlike in other species, the glands are solely apocrine without a sebaceous component. Branched tubules empty into collecting ducts and enter the anal canal at the anorectal junction. The secretion is mucus, protein, and lipid-rich. The large size and productive nature of the glands suggest that, like anal glands in other species, these may be used for signal transmission. This is the first detailed description of anal glands in a fully aquatic mammal.