Abstract
The Florida manatee, Trichechus manatus latirostris, is an endangered, fully aquatic, herbivorous mammal. It has long been hypothesized that the manatee uses chemical signaling for communication and broadcasts reproductive signals.1 Expressing reproductive state through excretions of the anal gland has been demonstrated in a variety of aquatic fish species2 and terrestrial mammals3-5 but not fully aquatic mammals.6 The manatee has been discovered to have diffuse, large, apocrine glands at the rectoanal junction and will be the first fully aquatic mammal to have these glands characterized. The goal of this study is to determine the morphology of the glands and infer function through comparison to other species. In addition, potential health risks associated with the glands are hypothesized.
Samples were collected from eleven naturally deceased manatees of varying ages, 6 female and 5 male. The anus and surrounding tissue were removed from the sphincter to several centimeters below the recto-anal junction with three centimeter margins. The glands and ducts were examined grossly, embedded in paraffin, sectioned at 5 µm, and stained with H&E, PAS, or Trichrome.
These glands are present in fetal, juvenile and adult male and female manatees. They are diffuse and found in clusters over a large area on either side of the anal canal within the muscle. The glands are apocrine, branched tubules that empty into large bilayered collecting ducts. The secretion is mucus, protein and lipid rich.
The large size and productive nature suggests that these glands are in use and important tissues for the manatee. Our findings indicate that the glands are primarily for signal transduction. The potential health concerns associated with anal glands include anal fistulas and cancerous tumors as observed in cats7 and dogs.8 Therefore, attention should be paid to anal gland health during post-mortem evaluation of manatees to determine prevalence of these conditions.
Acknowledgments
Thank you to Patricia Lewis for her histological expertise; the marine mammal pathobiology laboratory staff especially Dr. Martine Dewit and Chris Torno for sample collection. Thank you to Dr. Lisa Farina who observed these glands for the first time during a manatee necropsy. Funding is provided through the Florida Fish and Wildlife Conservation Commission, Whitney Marine Laboratory for Marine Bioscience and the University of Florida Aquatic Animal Health Program, the University of Florida College of Veterinary Medicine and Sigma Xi-Grant in Aid of Research. Research completed under US Fish and Wildlife permit #: MA067116-1 and MA066878-0, UF IACUC Study #: 200902684.
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