Dzyuba Viktoriya, Sampels Sabine, Ninhaus-Silveira Alexandre, Kahanec Martin, Veríssimo-Silveira Rosicleire, Rodina Marek, Cosson Jacky, Boryshpolets Sergii, Selinger Martin, Sterba Jan, Dzyuba Borys
University of South Bohemia in České Budějovice, Faculty of Fisheries and Protection of Waters, Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses, Zátiší 728/II, 389 25, Vodňany, Czech Republic.
University of South Bohemia in České Budějovice, Faculty of Fisheries and Protection of Waters, Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses, Zátiší 728/II, 389 25, Vodňany, Czech Republic; Swedish University of Agricultural Sciences, Department of Molecular Sciences, PO Box 7015, 75007, Uppsala, Sweden.
Theriogenology. 2019 May;130:26-35. doi: 10.1016/j.theriogenology.2019.02.029. Epub 2019 Mar 2.
All extant groups of Elasmobranches have internal fertilization and the structure of the male reproductive organs is very specific: sperm passes from the internal organs via the cloaca, but the male copulating organ (clasper) is distant from the cloaca. This suggests that sperm can contact the surrounding medium before fertilization. Because of this involvement with the environment, external signaling in sperm motility activation could occur in these species even though their fertilization mode is internal. In this case, spermatozoa of Elasmobranches should hypothetically possess a specific structure and membrane lipid composition which supports physiological functions of the sperm associated with environmental tonicity changes occurring at fertilization. Additionally, sperm motility properties in these taxa are poorly understood. The current study examined sperm lipid composition and motility under different environmental conditions for the ocellate river stingray, Potamotrygon motoro, an endemic South America freshwater species. Sperm samples were collected from six mature males during the natural spawning period. Sperm motility was examined in seminal fluid and fresh water by light video microscopy. Helical flagellar motion was observed in seminal fluid and resulted in spermatozoon progression; however, when diluted in fresh water, spermatozoa were immotile and had compromised structure. Lipid class and fatty acid (FA) composition of spermatozoa was analyzed by thin layer and gas chromatography. Spermatozoa FAs consisted of 33 ± 1% saturated FAs, 28 ± 1% monounsaturated FAs (MUFAs), and 41 ± 1% polyunsaturated FAs (PUFAs), and a high content of n-6 FAs (32 ± 2%) was measured. These results allowed us to conclude that sperm transfer from P. motoro male into female should occur without coming into contact with the hypotonic environment so as to preserve potent motility. In addition, this unusual reproductive strategy is associated with specific spermatozoa structure and lipid composition. Low level of docosahexaenoic acid and relatively low PUFA/MUFA ratio probably account for the relatively low fluidity of freshwater stingray membrane and can be the main reason for its low tolerance to hypotonicity.
所有现存的板鳃亚纲动物群体都进行体内受精，雄性生殖器官的结构非常特殊：精子从内部器官经泄殖腔排出，但雄性交配器官（交合突）与泄殖腔相距较远。这表明精子在受精前可能会接触周围介质。由于与环境有这种关联，即使这些物种的受精方式是体内受精，精子运动激活中的外部信号传导也可能发生。在这种情况下，板鳃亚纲动物的精子理论上应具有特定的结构和膜脂组成，以支持与受精时发生的环境渗透压变化相关的精子生理功能。此外，这些分类群中精子的运动特性了解甚少。本研究针对南美特有的淡水物种——眼斑河魟（Potamotrygon motoro），检测了不同环境条件下精子的脂质组成和运动情况。在自然产卵期从六只成年雄性个体采集精子样本。通过光学视频显微镜检查精液和淡水中的精子运动。在精液中观察到螺旋状鞭毛运动，并导致精子前进；然而，当稀释于淡水中时，精子无法运动且结构受损。通过薄层色谱法和气相色谱法分析精子的脂质类别和脂肪酸（FA）组成。精子脂肪酸由33±1%的饱和脂肪酸、28±1%的单不饱和脂肪酸（MUFA）和41±1%的多不饱和脂肪酸（PUFA）组成，且测得n-6脂肪酸含量较高（32±2%）。这些结果使我们得出结论，眼斑河魟雄性向雌性的精子传递应在不接触低渗环境的情况下发生，以保持有效的运动能力。此外，这种不寻常的生殖策略与特定的精子结构和脂质组成有关。二十二碳六烯酸水平较低以及相对较低的PUFA/MUFA比值可能是淡水魟鱼膜流动性相对较低的原因，并且可能是其对低渗耐受性低的主要原因。
