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標題: 蛇蘚精子傳播的生物力學:精子噴發的運動分析與生態效應
Biomechanics of sperm dispersal in Conocephalum conicum: Dynamics and ecological consequences of violent sperm discharge
作者: 王惟聖
Wei-Sheng Wang
關鍵字: 生物力學;蛇蘚;精子噴發;精子傳播;流體力學;運動分析;噴嘴;噴霧;biomechanics;Conocephalum conicum;sperm discharge;sperm dispersal;fluid dynamics;dynamic analysis;nozzle;spray
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傳播種實是植物必須面臨的重要挑戰,對底層的植物而言,讓孢子或花粉突破邊界層是最大的問題,因此部分植物發展出不同的孢子或花粉發射系統。本研究以蛇蘚 (Conocephalum conicum) 的精子噴發為研究對象,探討生物力學因子對地錢精子噴發運動的影響與生態效應。我成功拍攝到世界第一部蛇蘚精子噴發的高速影片,從中擷取精子雲運動軌跡,並用流體力學模型擬合,再將其運動相關資訊配合天氣資料來估計傳播範圍。典型的精子噴發會將精液從直徑約5 μm的孔洞以8.77±3.31 m/s的初速射出,並霧化成液滴直徑約20 μm的精子雲。精子雲的最大噴發高度高於具相同直徑的單一顆粒之預測彈道高度;雖其運動軌跡可以用阻力係數為定值的流體阻力模型擬合,但識別半徑值小於實驗估算值約一到二個數量級,顯示蛇蘚精子噴發時受到空氣動力的助益。在蛇蘚雄器成熟的季節,在邊界層生成的2公尺內,蛇蘚精子雲的平均噴發高度3.1公分超過由軟風及輕風的環境風級所估計的邊界層厚度。在輕風環境下,精子可受風力傳播超過6公尺遠。精子雲傳播範圍大小受噴發高度、液滴顆粒大小及環境風速的變異所影響,其中環境風速的影響最為顯著。與經典的噴發植物泥炭苔進行阻力係數及其他運動參數比較後,發現蛇蘚採用不同的噴發策略:透過微小的噴發孔才能使精液霧化,然此設計拉長噴發時間;前端液滴加速周圍空氣,可使後繼精子受到更小的空氣阻力,在增長的噴發時間作用下,因而能移動得更遠。前人關於植物傳播的研究未曾探討過液體精子顆粒的噴發力學機制,此研究為植物噴發傳播開啟研究新頁,並可成為仿生噴發裝置的靈感來源。

How to disperse seeds and spores is a big question for the plants. For the dwelling species, one of the major challenges is to make pollens or spores break through the boundary layer, for which some groups have developed discharging systems as solution. This study took the first ever high speed video recording of sperm discharge in liverwort Conocephalum conicum, and examined its biomechanical factors and the ecological consequences. I fitted the tracked penetration trajectory of the sperm cloud from videos with fluid dynamic models, and took kinematic and climate data to estimate the dispersal range. A simple discharge makes sperms have initial velocity at 8.77±3.31 m/s from the opening of 5 μm in width, and atomizes them to droplets of 20 μm in diameter. The sperm clouds could reach a height greater than what the ballistics model would predict for a single particle. Constant drag fluid dynamic model provided good fitting for the penetration trajectory, but underestimated the particle size one to two orders of magnitude, suggesting that C. conicum might have aerodynamics advantage in sperm discharge. During the mature season of antheridial disk of C. conicum, the ambient wind of light air or light breeze would generate boundary layer with thickness less than 3.1 cm, the average discharging height, at 2 m downstream from the start of the boundary layer; therefore, the discharged sperm would break through the boundary layer. Light breeze could transport the sperm for over 6 m horizontally. The dispersal range could be affected by the variance of particle radius, discharging height, and especially the wind speed. Comparison of the drag coefficient and discharging kinematic parameters with the classic discharging plants Sphagnum (peat moss) reveals that C. conicum has a different discharging strategy. In C. conicum, to atomize the sperm fluids through a small opening, long discharging duration would promote the frontal sperm droplets to accelerate the surrounding air, which further makes the succeeding sperm droplets reach a greater height. This first study on discharge of fluid particles in plants provides new insights into the dispersal mechanics in plants, as well as bio-inspired spray design for various needs.
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