Oviduct Morphology and Prolactin Receptor Expression in North American River Otters (Lontra canadensis) and Asian Small-Clawed Otters (Aonyx cinerea)
Otter populations worldwide have been declining due to environmental pressures and habitat loss. Gaps in knowledge of their reproductive physiology have slowed captive breeding efforts. The North American river otter (NARO), Lontra canadensis, and the Asian small-clawed otter (ASCO), Aonyx cinerea, have two distinct reproductive cycles. The NARO is monoestrous and seasonal with a marked embryonic diapause, whereas the ASCO is polyestrous and nonseasonal and lacks delayed implantation. There is little information available on the role of the oviduct in diapause or mustelid reproductive physiology. It was hypothesized that the NARO and ASCO would differ in oviduct length and in uterine and ovarian prolactin receptor expression. Oviducts from archived tracts held by the Reproductive Health Surveillance Program from both species (ASCO, n=14; NARO, n=5) were dissected, the length measured and compared. The oviducts were then trimmed into cross-sectional segments and processed for comparison of histomorphology. The uterus and ovaries from a subset were processed and labeled with antibodies for prolactin (PRL) receptor. The stain intensity was scored at four locations (uterine epithelium, uterine glandular epithelium, ovarian parenchyma, and ovarian follicular structures) and compared. Findings were: 1) NARO oviducts were significantly longer than ASCO oviducts (p=0.0085); 2) PRL receptor antibodies successfully labeled otter reproductive tissues; and 3) there was no significant difference in PRL receptor expression between NARO and ASCO reproductive tissues on preliminary analysis. Knowledge of the reproductive tract, in particular physiology of diapause, allows for improved reproductive interventions in these threatened species.
The authors appreciate the help of Amy Porter and Kathy Joseph, Michigan State University Investigative Histopathology Lab; Stephanie French, DVM; and our funders: American Association of Zoo Veterinarians, Merial Veterinary Scholars Summer Research Program, Association of Zoo and Aquariums. In addition, the authors thank the AZA Institutions that provided tissues: Atlanta Zoo, Children Zoo at Celebration Square, Columbus Zoo, Dallas Zoo, Denver Zoo, Houston Zoo, Jacksonville Zoo, Red River Zoo, Roger Williams Park Zoo, Six Flags Discovery Kingdom, and Sunset Zoo in Manhattan, KS. Authors also are grateful to the AAZV for continued financial support of the RHSP and this otter project.