Stoltz J A, Neff B D
Department of Biology, University of Western Ontario, London, Ontario, Canada.
J Evol Biol. 2006 Nov;19(6):1873-81. doi: 10.1111/j.1420-9101.2006.01165.x.
The role of sperm number and quality in male competitiveness was investigated using in vitro fertilization experiments with bluegill (Lepomis macrochirus). Bluegill males use one of three mating tactics: 'sneakers', which streak spawn; 'satellites', which mimic females; and 'parentals', which are territorial. The in vitro experiments mimicked natural spawning by incorporating these males' mean proximity to eggs and timing of sperm release. Using a maximum-likelihood algorithm, raffle equations were fit to paternity data, which revealed a strong effect of sperm number on male competitiveness. There was no difference in sperm flagellum length, curvilinear swim speed or path linearity among the three male mating types, and these traits did not explain any additional variation in male competitiveness. It was estimated that, given closer proximity to eggs, satellites need release only 0.34 times as many sperm as parentals to obtain equal paternity. Despite being farther from the eggs and releasing sperm about half a second after parentals, sneakers need only release 0.58 times as many sperm as parentals to obtain equal paternity. Thus, the increased competitiveness of sneakers' sperm must come from a component of sperm quality other than speed or length.
利用蓝鳃太阳鱼（Lepomis macrochirus）的体外受精实验，研究了精子数量和质量在雄性竞争中的作用。蓝鳃太阳鱼雄性采用三种交配策略之一：“偷情者”，即在雌鱼产卵时偷偷排精；“卫星鱼”，即模仿雌鱼；以及“亲代鱼”，即占据领地。体外实验通过纳入这些雄鱼与卵子的平均接近程度和精子释放时间，模拟了自然产卵过程。使用最大似然算法，将抽奖方程拟合到亲子鉴定数据上，结果显示精子数量对雄性竞争力有很强的影响。三种雄性交配类型的精子鞭毛长度、曲线游动速度或路径线性度没有差异，这些特征也无法解释雄性竞争力的任何额外变化。据估计，如果更接近卵子，“卫星鱼”只需释放亲代鱼0.34倍数量的精子就能获得相同的父权。尽管“偷情者”离卵子更远，且在亲代鱼之后约半秒释放精子，但它们只需释放亲代鱼0.58倍数量的精子就能获得相同的父权。因此，“偷情者”精子竞争力的提高必定来自于速度或长度之外的精子质量成分。
