School of Marine Sciences, University of Maine, Orono, Maine 04469, USA.
Evolution. 2009 Dec;63(12):3114-23. doi: 10.1111/j.1558-5646.2009.00784.x. Epub 2009 Jul 28.
Male gain curves describe the relationship between allocation to sperm production and male reproductive success and are central to models of sex allocation in hermaphrodites. Sperm competition is expected to result in more linear gains and select for increased allocation. We hypothesized that high sperm production in passively mating systems may also be the result of selection to enhance the ability to fertilize distant ova. Consequently, we explored the effect of distance on male gain curves in a free-spawning colonial ascidian. The performance of focal males that varied in sperm production was assayed at three distances via microsatellite markers. An advection-diffusion model was used to estimate sperm concentration gradients, to predict male reproductive gain integrated across multiple downstream females, and explore effects of hydrodynamic conditions. As distance increased, male reproductive success decreased and empirical gain curves became increasingly linear. Our model predicted that the expected net gain curve is relatively insensitive to variation in flow regime and will saturate much more slowly than if only a single, nearby distance is considered. Thus, high levels of sperm production may enhance fitness both in competitive situations and with increasing fertilization distance, highlighting the need to consider distance effects when evaluating gain curves.
雄性收益曲线描述了精子生产分配与雄性生殖成功之间的关系，是雌雄同体动物性别分配模型的核心。精子竞争预计会导致更线性的收益，并选择增加分配。我们假设在被动交配系统中高精子产量也可能是选择增强远距离卵子受精能力的结果。因此，我们在一个自由产卵的群体海鞘中探索了距离对雄性收益曲线的影响。通过微卫星标记，在三个距离处检测了精子产量不同的焦点雄性的表现。使用平流扩散模型来估计精子浓度梯度，预测雄性生殖的整体收益，以及探索水动力条件的影响。随着距离的增加，雄性生殖成功率降低，经验收益曲线变得越来越线性。我们的模型预测，预期的净收益曲线对流动状态的变化相对不敏感，并且比只考虑单一的、附近的距离时饱和得慢得多。因此，高水平的精子生产可能会在竞争情况下和随着受精距离的增加而提高适应性，这突出了在评估收益曲线时需要考虑距离效应。
