Yeh Shu-Dan, Chan Carolus, Ranz José M
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, USA.
J Vis Exp. 2013 Aug 22(78):e50547. doi: 10.3791/50547.
Competition among conspecific males for fertilizing the ova is one of the mechanisms of sexual selection, i.e. selection that operates on maximizing the number of successful mating events rather than on maximizing survival and viability. Sperm competition represents the competition between males after copulating with the same female, in which their sperm are coincidental in time and space. This phenomenon has been reported in multiple species of plants and animals. For example, wild-caught D. melanogaster females usually contain sperm from 2-3 males. The sperm are stored in specialized organs with limited storage capacity, which might lead to the direct competition of the sperm from different males. Comparing sperm competitive ability of different males of interest (experimental male types) has been performed through controlled double-mating experiments in the laboratory. Briefly, a single female is exposed to two different males consecutively, one experimental male and one cross-mating reference male. The same mating scheme is then followed using other experimental male types thus facilitating the indirect comparison of the competitive ability of their sperm through a common reference. The fraction of individuals fathered by the experimental and reference males is identified using markers, which allows one to estimate sperm competitive ability using simple mathematical expressions. In addition, sperm competitive ability can be estimated in two different scenarios depending on whether the experimental male is second or first to mate (offense and defense assay, respectively), which is assumed to be reflective of different competence attributes. Here, we describe an approach that helps to interrogate the role of different genetic factors that putatively underlie the phenomenon of sperm competitive ability in D. melanogaster.
同种雄性之间为使卵子受精而展开的竞争是性选择的机制之一，即这种选择作用于使成功交配事件的数量最大化，而非使生存和活力最大化。精子竞争指的是雄性在与同一雌性交配后彼此之间的竞争，在此过程中它们的精子在时间和空间上同时存在。这种现象在多种动植物物种中都有报道。例如，野外捕获的黑腹果蝇雌性通常含有来自2至3只雄性的精子。精子储存在储存能力有限的特殊器官中，这可能导致不同雄性的精子直接竞争。通过实验室中的控制性双重交配实验，对不同感兴趣雄性（实验雄性类型）的精子竞争能力进行了比较。简而言之，将一只雌性依次暴露于两只不同的雄性，一只实验雄性和一只杂交参考雄性。然后对其他实验雄性类型采用相同的交配方案，从而通过共同参考间接比较它们精子的竞争能力。使用标记物确定由实验雄性和参考雄性所生后代的比例，这使得人们能够用简单的数学表达式来估计精子竞争能力。此外，根据实验雄性是第二个还是第一个交配（分别为进攻和防御测定），可以在两种不同情况下估计精子竞争能力，这被认为反映了不同的能力属性。在此，我们描述一种方法，该方法有助于探究不同遗传因素在黑腹果蝇精子竞争能力现象中可能发挥的作用。
