Randerson J P, Hurst L D
Department of Biology and Biochemistry, Bath University, Claverton Down, UK.
Proc Biol Sci. 2001 Apr 22;268(1469):879-84. doi: 10.1098/rspb.2000.1581.
Why are sperm small and eggs large? The dominant explanation for the evolution of gamete size dimorphism envisages two opposing selection pressures acting on gamete size: small gametes are favoured because many can be produced, whereas large gametes contribute to a large zygote with consequently increased survival chances. This model predicts disruptive selection on gamete size (i.e. selection for anisogamy) if increases in zygote size confer disproportional increases in fitness (at least over part of its size range). It therefore predicts that increases in adult size should be accompanied by stronger selection for anisogamy. Using data from the green algal order Volvocales, we provide the first phylogenetically controlled test of the model's predictions using a published phylogeny and a new phylogeny derived by a different method. The predictions that larger organisms should (i) have a greater degree of gamete dimorphism and (ii) have larger eggs are broadly upheld. However, the results are highly sensitive to the phylogeny and the mode of analysis used.
为什么精子小而卵子大？对于配子大小二态性进化的主流解释设想了两种作用于配子大小的相反选择压力：小配子受青睐是因为可以产生很多，而大配子有助于形成大的合子，从而增加生存机会。该模型预测，如果合子大小的增加带来不成比例的适合度增加（至少在其部分大小范围内），则对配子大小会进行分裂选择（即对异配生殖的选择）。因此，它预测成年个体大小的增加应伴随着对异配生殖更强的选择。利用来自绿藻目团藻目的数据，我们使用已发表的系统发育树和通过不同方法得出的新系统发育树，首次对该模型的预测进行了系统发育控制检验。较大生物体应该（i）具有更大程度的配子二态性和（ii）具有更大卵子的预测在很大程度上得到了支持。然而，结果对系统发育树和所使用的分析模式高度敏感。
