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Study yields insights into Florida manatee sperm that may impact species’ reproductive health

Understanding what is “normal” in regard to sperm characteristics, such as sperm morphology, morphometry, and structure, is critical in order to assess the reproductive health of individuals within a population. This is especially important for the management and conservation of protected species, such as the Florida manatee, where information of this nature is extremely limited.

In a new study published in The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, an official publication of the American Association for Anatomy, Drs. Jonathan Cowart and Iske Larkin, both of UF’s Aquatic Animal Health Program, and their collaborators investigate the morphology, morphometry, and ultrastructure of Florida manatee sperm. To do so, they used computer-aided sperm morphology analysis, laser-scanning confocal microscopy and electron microscopy.

A total of 1,800 sperm from nine different manatees were analyzed to reveal new morphometric and structural data for Florida manatee sperm, all of which provide new insights into how evolutionary pressures affect sperm structure and function in this marine mammal species.

“The structural results of this study yielded many new observations on Florida manatee sperm that help support the potential occurrence of sperm competition in this species, which is the result of a promiscuous mating system,” said Cowart, a postdoctoral research associate who works with Larkin, a lecturer and educational coordinator for the AAH program at the UF College of Veterinary Medicine.

Among the key observations the team made were:

• Preliminary measurements of sperm midpiece volume correlated closely with other species that exhibit a multi-partner mating system
• Distinct enlargement of outer dense fibers 1, 5, 6, and 9, which were uniquely elongated and rectangular in shape, and
• Localization of cytoskeletal elements (F-actin filaments and alpha-tubulin microtubules) in structurally important locations across the spermatozoon.

“The combination of these structural characteristics may function to stabilize the sperm flagellum and enhance sperm velocity while also maintaining sperm integrity and morphology as it transits the female reproductive tract,” Cowart said. “These results provide new insights into how a promiscuous mating system may influence sperm structure and function in the Florida manatee.”

Read the full paper here.