Kobayashi Shiro, Inoue Ken, Kato Masahiro
Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Biological Institute and Herbarium, Faculty of Science, Shinshu University, Matsumoto, 390-8621, Japan.
Evolution. 1999 Jun;53(3):752-757. doi: 10.1111/j.1558-5646.1999.tb05369.x.
A previous study of Campanula punctata pollinated by Bombus diversus showed greater male reproductive success in plants with wider corollas when male reproductive success was measured by paternity analysis. Pollen removal alone was not a good measure of male reproductive success. The aim of the current study is to elucidate the mechanism underlying the selection on corolla width in C. punctata. Multiple regression analysis of male reproductive success in experimental populations revealed that the advantage of a wide corolla to the male is independent of the corolla width of pollen recipients, indicating that the position of pollen deposited on Bombus may not be an important factor for selection. However, the number of pollen grains that fell on the petal or off the flower and were lost at the first visit of Bombus (pollen fall) decreased with increasing corolla width, so that most pollen grains removed from a wide flower were deposited onto the pollinator. In a narrow flower, a greater proportion of the pollen removed was wasted through pollen fall. Pollen removal does not reflect male reproductive success, at least in part because of the loss of pollen in some flowers through pollen fall. The positive relationship between wider corollas and reduced loss of pollen through pollen fall is likely to lead to greater male reproductive success of wider flowers under repeated visits of pollinators. Decreased pollen fall, probably due to more gentle contact between pollen and bees in flowers with wider corollas, may be one of the mechanisms underlying the selection on corolla width of C. punctata.
之前一项关于被黑尾熊蜂授粉的斑叶风铃草的研究表明，当通过父本分析来衡量雄性繁殖成功率时，花冠较宽的植株具有更高的雄性繁殖成功率。仅花粉去除情况并不能很好地衡量雄性繁殖成功率。本研究的目的是阐明斑叶风铃草花冠宽度选择背后的机制。对实验种群中雄性繁殖成功率的多元回归分析表明，宽花冠对雄性的优势与花粉接受者的花冠宽度无关，这表明花粉在熊蜂身上的沉积位置可能不是选择的重要因素。然而，在熊蜂首次访花时落在花瓣上或掉落在花外而损失的花粉粒数量（花粉掉落）随着花冠宽度的增加而减少，因此从宽花上移除的大多数花粉粒都沉积在了传粉者身上。在窄花中，移除的花粉中有更大比例因花粉掉落而被浪费。花粉去除情况并不能反映雄性繁殖成功率，至少部分原因是一些花朵中的花粉因花粉掉落而损失。在传粉者多次访花的情况下，较宽的花冠与减少因花粉掉落而导致的花粉损失之间的正相关关系可能会使宽花具有更高的雄性繁殖成功率。花粉掉落减少，可能是由于花冠较宽的花朵中花粉与蜜蜂之间的接触更轻柔，这可能是斑叶风铃草花冠宽度选择背后的机制之一。
