Evans Jonathan P
Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Nedlands, Perth, 6009, WA, Australia.
Naturwissenschaften. 2009 Jul;96(7):771-9. doi: 10.1007/s00114-009-0529-6. Epub 2009 Mar 24.
Sperm competition theory predicts that males should tailor their investment in ejaculates according to the number of rival males competing to fertilize a female's eggs. Research spanning several taxa supports this prediction by showing that males are often sensitive to the level of sperm competition and adjust their investment in sperm numbers accordingly. More recent work has revealed that males may also tailor the quality of sperm according to the number of males competing for fertilization. Here I test for both effects in guppies (Poecilia reticulata) in an experiment that simultaneously evaluates the risk and intensity models of sperm competition. The experiment determined whether male guppies adjust the number (stripped ejaculate size) and quality (sperm velocity and viability) of sperm that are primed over a 3-day period according to experimental changes in the perceived level of sperm competition. A total of 136 focal males were initially stripped of all retrievable sperm and assayed for these sperm traits before being allocated at random to one of four treatments simulating different levels of sperm competition risk and intensity. During the 3-day treatment phase, focal males had visual and olfactory access to a sexually receptive (initially virgin) female maintained with different numbers of stimulus males to simulate variation in the risk and intensity of sperm competition. Following this, males were assayed again for the sperm traits. Contrary to predictions, there was no significant change in any of the measured variables among treatments, although qualitatively the patterns for sperm velocity and viability did conform to expectation. The lack of any trend for the number of sperm primed was unequivocal and future work examining the effects of sperm competition on sperm production should focus on whether males differentially allocate sperm numbers among matings that differ in the level of sperm competition.
精子竞争理论预测，雄性应根据竞争使雌性交配受孕的雄性对手数量来调整其在射精方面的投入。跨越多个分类群的研究支持了这一预测，研究表明雄性通常对精子竞争水平敏感，并据此调整其在精子数量上的投入。最近的研究还表明，雄性可能还会根据竞争受精的雄性数量来调整精子质量。在此，我在一项同时评估精子竞争风险和强度模型的实验中，对孔雀鱼（孔雀花鳉）的这两种效应进行了测试。该实验确定了雄性孔雀鱼是否会根据所感知到的精子竞争水平的实验变化，来调整在3天时间内准备好的精子数量（去除精清后的射精量）和质量（精子速度和活力）。总共136只作为研究对象的雄性孔雀鱼最初被去除了所有可采集到的精子，并对这些精子特征进行了测定，然后被随机分配到四种处理方式之一，以模拟不同水平的精子竞争风险和强度。在为期3天的处理阶段，作为研究对象的雄性孔雀鱼可以通过视觉和嗅觉接触到一只性成熟（最初为处女）的雌性孔雀鱼，该雌性与不同数量的刺激雄性孔雀鱼放在一起，以模拟精子竞争风险和强度的变化。在此之后，再次对雄性孔雀鱼的精子特征进行测定。与预测相反，各处理组之间在任何测量变量上均无显著变化，尽管在精子速度和活力的定性模式上确实符合预期。准备好的精子数量缺乏任何变化趋势是明确无疑的，未来研究精子竞争对精子产生影响的工作应关注雄性是否在精子竞争水平不同的交配中差异分配精子数量。
