Delesalle V A, Mazer S J, Paz H
Department of Biology, Gettysburg College, Gettysburg, PA, USADepartment of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, USACentro de Investigaciones en Ecosistemas, Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico.
J Evol Biol. 2008 Jan;21(1):310-323. doi: 10.1111/j.1420-9101.2007.01444.x. Epub 2007 Nov 12.
Among plants, pairs of selfing vs. outcrossing sister taxa provide interesting systems in which to test predictions concerning the magnitude and direction of temporal changes in sex allocation. Although resource availability typically declines towards the end of the growing season for annual taxa, temporal changes in mating opportunities depend on mating system and should change less in selfing taxa. Consequently, given that the pollen:ovule (P:O) ratio of flowers reflects the investment in (and potential fitness pay-off due to) male vs. female function, we predicted that the P:O ratio should also be less variable among and within selfers than in closely related outcrossers. To test these predictions, we measured temporal changes in sex allocation in multiple field populations of two pairs of sister taxa in the annual flowering plant genus Clarkia (Onagraceae). In the outcrossing Clarkia unguiculata and the selfing Clarkia exilis, ovule production declined similarly from early to late buds, whereas pollen production remained constant or increased in the outcrosser but remained constant or decreased in the selfer. Consequently, the P:O ratio increased within unguiculata populations but marginally increased or stayed constant in exilis populations. In all populations of the selfing Clarkia xantiana spp. parviflora and the outcrossing C. x. spp. xantiana, both ovule and pollen production per flower declined over time. The effects of these declines on the P:O ratio, however, differed between subspecies. In each xantiana population, the mean P:O ratio did not differ between early and late flowers, although individuals varied greatly in the direction and magnitude of phenotypic change. By contrast, parviflora populations differed in the mean direction of temporal change in the P:O ratio. We found little evidence to support our initial predictions that the P:O ratio of the selfing taxa will consistently vary less than in outcrossing taxa.
在植物中，自交与异交的姊妹分类群对为测试有关性别分配时间变化的幅度和方向的预测提供了有趣的系统。尽管对于一年生分类群而言，生长季末期资源可用性通常会下降，但交配机会的时间变化取决于交配系统，并且在自交分类群中变化应该较小。因此，鉴于花的花粉：胚珠（P：O）比率反映了对雄性与雌性功能的投入（以及潜在的适合度回报），我们预测，与亲缘关系相近的异交植物相比，自交植物种内和种间的P：O比率变化也应较小。为了验证这些预测，我们测量了一年生开花植物克拉花属（柳叶菜科）两对姊妹分类群多个田间种群中性别分配的时间变化。在异交的细叶克拉花和自交的艾氏克拉花中，从早期花蕾到晚期花蕾，胚珠产量下降情况相似，而异交种的花粉产量保持不变或增加，自交种的花粉产量保持不变或减少。因此，细叶克拉花种群内的P：O比率增加，而艾氏克拉花种群内的P：O比率略有增加或保持不变。在自交的小花克拉花和异交的黄花克拉花的所有种群中，每朵花的胚珠和花粉产量均随时间下降。然而，这些下降对P：O比率的影响在不同亚种之间存在差异。在每个黄花克拉花种群中，早期花和晚期花的平均P：O比率没有差异，尽管个体在表型变化的方向和幅度上差异很大。相比之下，小花克拉花种群在P：O比率时间变化的平均方向上存在差异。我们几乎没有找到证据支持我们最初的预测，即自交分类群的P：O比率变化始终小于异交分类群。
