Waser Nickolas M, Fugate Michael L
Department of Biology, University of California, 92521, Riverside, CA, USA.
Rocky Mountain Biological Laboratory, 81224, Crested Butte, CO, USA.
Oecologia. 1986 Nov;70(4):573-577. doi: 10.1007/BF00379906.
Previous experiments showed that the sympatric herbs Delphinium nelsonii and Ipomopsis aggregata compete for hummingbird pollination and that deleterious effects of the former species on seed set of the latter involve interspecific pollen transfer. However, seed set was not reduced when pollen of both species was applied simultaneously to I. aggregata stigmas. Hence a competitive effect may require arrival of foreign pollen before conspecific pollen. To explore this possibility we subjected I. aggregata flowers to a "competition" treatment in which they received D. nelsonii pollen 6 h before I. aggregata pollen, or to a "control" in which they received only the conspecific pollen. Foreign pollen precedence decreased mean seed set by almost 50%, which is consistent with effects observed in previous experiments. Reduced seed set can be explained by the fact that foreign pollen often caused stigma lobes to close together within 1.5-6 h, reducing subsequent receptivity. Stigma closure was also elicited by conspecific pollen, but not by mechanical stimulation, and was influenced by size of the pollen load and identity of the plant being pollinated.
先前的实验表明，同域分布的草本植物纳尔逊翠雀花和聚花翠距花会竞争蜂鸟传粉，且前者对后者结实的有害影响涉及种间花粉转移。然而，当将两种植物的花粉同时施加到聚花翠距花的柱头上时，结实并未减少。因此，竞争效应可能需要外来花粉先于同种花粉到达。为探究这种可能性，我们对聚花翠距花进行了“竞争”处理，即先让其接受纳尔逊翠雀花的花粉6小时，之后再接受聚花翠距花自身的花粉，同时设置了“对照”处理，即只让其接受同种花粉。外来花粉先于同种花粉到达使平均结实率降低了近50%，这与先前实验中观察到的结果一致。结实率降低可归因于外来花粉常常在1.5至6小时内导致柱头裂片闭合，从而降低了后续的可受性。同种花粉也会引发柱头闭合，但机械刺激不会，而且柱头闭合受花粉量大小以及被授粉植物的身份影响。
