Abstract
Limited information is available regarding male reproductive physiology in West Indian manatees (Trichechus manatus). Currently, only basic ultrastructural and morphometric descriptions of the spermatozoon exist; however, there are no reports evaluating any seminal characteristics in this species. Therefore, the aim of the study was to fill current gaps in knowledge regarding semen parameters in West Indian manatees by collecting and characterizing multiple ejaculate samples from a single, adult West Indian manatee. Samples were analyzed for the following semen parameters: volume, agglutination, pH, osmolality, viscosity, concentration, total sperm number, motility and kinematic parameters, morphology, plasma membrane integrity, acrosome integrity, chromatin maturation, and chromatin condensation. All macroscopic semen parameters varied to some extent between samples. Total and progressive motility was high for ejaculates 2 to 5, exceeding 97 and 89%, respectively; however, these parameters decreased dramatically throughout ejaculates 6 and 7. Across all samples, curvilinear velocity, straight-line velocity, and average pathway velocity represented the largest significant differences (p < 0.001) between each of the progression velocity subgroups (rapid, medium, slow). Sperm characteristics, including acrosome integrity (79.8%), chromatin condensation (93.1%), and chromatin maturation (99.5%) were very high; however, high numbers of morphologically abnormal sperm were present (52.9%) and plasma membrane integrity was low (45.1%). These results are the first of their kind for this species and suggest high semen quality, based on multiple ejaculates, in this male West Indian manatee.
Highlights
The West Indian manatee (Trichechus manatus) is one of the most well-studied sirenian species
Unlike other marine mammals managed in zoological institutions and aquaria, such as the bottlenose dolphin (Tursiops truncatus), orca (Orcinus orca), and beluga (Delphinapterus leucas), no captive breeding program exists for manatees in the United States (U.S.), further limiting opportunities to better understand the reproductive physiology of this species
While some parameters were considered very good, other parameters were moderate to poor
Summary
The West Indian manatee (Trichechus manatus) is one of the most well-studied sirenian species. The geographic range of this species includes the coastal southeastern United States, Florida, Mexico through Central America, the Greater Antilles of the Caribbean, and the northern coasts of Colombia and Venezuela to eastern Brazil [1, 2]. Throughout its range, this species faces a myriad of anthropogenic and natural threats including watercraft collisions [3,4,5], entanglement. High investment in reproduction and slow reproductive rates are limiting factors for the continued growth of manatee populations and without a complete understanding of reproduction in this species, long-term management and conservation of this species is potentially at risk
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