Abstract
Information about genital anatomy of the male Florida manatee (Trichechus manatus latirostris) is scarce. Studies have been conducted on the gross and histological anatomy of the testis and epididymis; however, the accessory sex glands have not been analyzed in detail.3,6 The objectives of this study were to conduct an anatomical gross and histological description of the entire reproductive tract of male Florida manatee, including the testes, present accessory glands and penis.
Three reproductive tracts of adult males were collected for histological analysis, and three additional tracts (two adults and one juvenile) were for gross anatomical analysis, from the Marine Mammal Pathobiology Laboratory, in St. Petersburg, Tampa. Four archived tracts (two adults, a juvenile and an infant) were included for histological analysis. Gross anatomical descriptions of the tracts were determined by dissection. Histological analysis was made using the following stains: hematoxylin and eosin, PAS, Gomori's trichrome, and immunohistochemistry specific for smooth muscle actin.2,8 The male Florida manatee reproductive tract presented some anatomical similarities with different species. The accessory sex glands present are the seminal vesicles and prostate. The seminal vesicles are bilateral, well-developed, large lobulated vesicular glands, like the dugong (Dugong dugon).4 The prostate in the manatee male is similar to the stallion7 (Equus ferus), with small glands, paired laterally, located ventral to the urinary bladder and dorsal to the urethralis muscle. This gland was histologically defined as a mixed gland, like the ram (Ovis aries).1 Manatee appear to lack the ampullary gland like cats (Felis catus), boar (Sus sp.) and humans, and bulbourethral glands as in dogs (Canis l. familiaris).4,5,7 Accessory sex glands vary in size, shape and presence among the species. In the manatee, the seminal vesicles and prostate serve as the producer of seminal fluid, even in the absence of other accessory sex glands. This could be that the fructose and fluid components produced by these glands are enough to give energy and transport to the sperm. The adult penis of the manatee was approximately 15 inches long and 1.5 inches in width, and the os penis is absent in this species. The manatee penis has a major corpus cavernosum (dorsally located) and scarce corpus spongiosum near the penile urethra (ventromedially located), all surrounded by a thick tunica albuginea layer. This suggests that erection occurs by vascularization enlargement. Further investigation would be recommended with a larger number of specimens, to analyze the content of the accessory sex glands' fluids and evaluate possible features that could confirm the possibility of sperm competition in manatees.
Acknowledgements
The authors would like to thank the following people for their support of this project: Patricia Lewis, Dr. Malgorzata Prozor, Dr. Jeremy Delcambre, Dr. Claus Buergelt. Dr. Meghan Bills of the University of Florida - College of Veterinary Medicine, and Martine De Wit of FWC. The authors thank the College of Veterinary Medicine for financial support of this project and the CONACYT. Tissues were collected under IACUC Protocol #201307998 and the Aquatic Animal Health US Fish and Wildlife permit MA067116.
* Presenting author
+ Student presenter
Literature Cited
1. Bacha WJ, Wood LM. Color Atlas of Veterinary Histology. Lea & Febiger; 1990:269.
2. Carson F, Hladik C. Histotechnology: A Self-Instructional Text. 3rd ed. Chicago, IL: ASCP Press; 2009:304.
3. Hernandez P, Reynolds III JE, Marsh H, Marmontel M. Age and seasonality in spermatogenesis of Florida manatees. In: Federal Government Series: Information and Technology Report - Population Biology of the Florida Manatee (Trichechus manatus latirostris). U.S. Fish and Wildlife Service Population Biology of the Florida Manatee. 1995;1:84–95.
4. Marsh H, Heinsohn GE, Glover TD. Changes in the male reproductive organs of the dugong, Dugong dugon (Sirenia: Dugongidae) with age and reproductive activity. Aust J Zool. 1984;32:721–742.
5. Pineda MH, Faulkner LC. Male reproduction. In: Mc Donald LE. Veterinary Endocrinology and Reproduction. 3rd ed. Philadelphia, PA: Lea & Febiger; 1980:235–273.
6. Reynolds J, Rommel SA, Pitchford ME. The likelihood of sperm competition in manatees - explaining an apparent paradox. Mar Mamm Sci. 2004;20(3):464–476.
7. Senger PL. Pathways to Pregnancy and Parturition. Current Conceptions, Inc.; 1997:272.
8. Sheehan D, Hrapchak B. Theory and Practice of Histotechnology. 2nd ed. Columbus, OH: Battelle Press; 1987:481.