Department of Biology, Gettysburg College, Gettysburg, Pennsylvania 17325 USA.
Am J Bot. 2009 May;96(5):968-78. doi: 10.3732/ajb.0800039. Epub 2009 Apr 13.
Multiple field populations of two pairs of diploid sister taxa with contrasting mating systems in the genus Clarkia (Onagraceae) were surveyed to test predictions concerning the effects of resource status, estimated as plant size, on pollen and ovule production and on the pollen:ovule (P:O) ratio of flowers. Most theoretical models of size-dependent sex allocation predict that, in outcrossing populations, larger plants should allocate more resources to female function. Lower P:O ratios in larger plants compared to smaller plants have been interpreted as supporting this prediction. In contrast, we predicted that P:O ratio should not vary with plant size in predominantly selfing plants, in which each flower contributes to reproductive success equally through male and female function. We found that, in all four taxa, both ovule and pollen production per flower usually increased significantly with plant size and that the shape of this relationship was decelerating. However, ovule production either decelerated more rapidly than or at the same rate as pollen production with plant size. Consequently,the P:O ratio increased or had no relationship with plant size. This relationship was population-specific (not taxon-specific) and independent of the mating system. Possible explanations for the increasing maleness with plant size are discussed.
对两个二倍体姐妹种的两对多群体进行了调查，这些种在育性系统上存在差异，属于柳叶菜科（Onagraceae）。这些调查旨在检验关于资源状态（估计为植物大小）对花粉和胚珠产量以及花的花粉：胚珠（P:O）比的影响的预测。大多数关于大小依赖的性别分配的理论模型预测，在异交种群中，较大的植物应该将更多的资源分配给雌性功能。与较小的植物相比，较大的植物中较低的 P:O 比一直被解释为支持这一预测。相比之下，我们预测，在主要自交的植物中，P:O 比不应随植物大小而变化，因为每朵花都通过雄性和雌性功能平等地为繁殖成功做出贡献。我们发现，在所有四个种中，每朵花的胚珠和花粉产量通常都随植物大小显著增加，而且这种关系的形状呈减速趋势。然而，胚珠的产量要么比花粉的产量更快地减速，要么与花粉的产量以相同的速度减速。因此，P:O 比随植物大小增加或没有关系。这种关系是种群特异性的（不是种特异性的），与交配系统无关。对植物大小与雄性增加之间关系的可能解释进行了讨论。
