Functional morphology of venous structures associated with the male and female reproductive systems in Florida manatees (Trichechus manatus latirostris)

The reproductive organs of Florida manatees (Trichechus manatus latirostris ) are surrounded by thermogenic locomotory muscles and insulating fat. Mana tees are reported to maintain core body temperatures of 35.6 degrees -36.4 degrees C, temperatures known to interfere with production and maturation o f viable sperm in terrestrial mammals. We describe two novel venous plexuse s associated with the manatee epididymis. Each epididymis is located in a h ypogastric fossa at the caudolateral extremity of the abdominal cavity. Eac h hypogastric fossa is lined by an inguinal venous plexus that receives coo led blood from a superficial thoracocaudal plexus. We conclude that male ma natees may prevent hyperthermic insult to their reproductive tissues by fee ding cooled superficial blood to venous plexuses deep within their bodies. Female manatees also possess hypogastric fossae and venous structures simil ar to those found in male manatees. The ovaries, uterine tubes, and distal tips of the uterine horns are located in the hypogastric fossae. We suggest that the thermovascular structures we describe also prevent hypothermic in sult to female manatee reproductive tissues. The venous structures in manat ees are functionally similar to structures associated with reproductive the rmoregulation in cetaceans and phocid seals. Thus, these thermovascular str uctures appear to be convergent morphological adaptations that occur in thr ee clades of diving mammals with independent evolutionary histories. Anat R ec 264:339-347, 2001. Published 2001 Wiley-Liss, Inc.dagger.