Lymbery Rowan A, Kennington W Jason, Evans Jonathan P
Am Nat. 2018 Jul;192(1):94-104. doi: 10.1086/697447. Epub 2018 Apr 6.
The widespread prevalence of sperm competition means that ejaculates face intense sexual selection. However, prior investigations of sexual selection on gametes have been hampered by two difficulties: (1) deriving estimates of relative fitness from sperm competition trials that are comparable across rival male and female genotypes and (2) obtaining measures of competitive fertilization success that are not confounded by postzygotic effects. Here, we exploit the experimental tractability of a broadcast spawning marine invertebrate to overcome these challenges and characterize multivariate sexual selection on sperm traits when multiple ejaculates compete. In multimale spawning events, we tracked real-time success of sperm using fluorescent tags that are visible inside fertilized eggs. We then used multivariate selection analyses to identify patterns of linear and nonlinear sexual selection on multiple sperm morphology and motility traits. Specifically, we found nonlinear selection against divergent combinations of sperm length, velocity, and swimming path linearity. These patterns likely reflect the way different swimming strategies allow sperm to locate and track eggs. Our results demonstrate that there are overall patterns of selection on ejaculates across a biologically realistic range of ejaculate-ejaculate and ejaculate-female interactions; therefore, there is the potential for adaptive evolution of ejaculate traits under sperm competition.
精子竞争的广泛存在意味着射精面临着激烈的性选择。然而，先前对配子性选择的研究受到两个困难的阻碍：（1）从精子竞争试验中得出相对适合度的估计值，这些估计值要在不同的雄性和雌性基因型之间具有可比性；（2）获得不受合子后效应混淆的竞争性受精成功率的测量值。在这里，我们利用一种体外受精的海洋无脊椎动物的实验易处理性来克服这些挑战，并描述当多个射精相互竞争时精子性状的多变量性选择。在多雄性产卵事件中，我们使用在受精卵内可见的荧光标签跟踪精子的实时成功情况。然后，我们使用多变量选择分析来识别对多种精子形态和运动特征的线性和非线性性选择模式。具体来说，我们发现对精子长度、速度和游动路径线性度的不同组合存在非线性选择。这些模式可能反映了不同游动策略使精子定位和追踪卵子的方式。我们的结果表明，在射精 - 射精和射精 - 雌性相互作用的生物学现实范围内，射精存在总体选择模式；因此，在精子竞争下射精性状具有适应性进化的潜力。
