Fetscher A E
Department of Biology, University of California, San Diego, La Jolla 92093, USA.
Proc Biol Sci. 2001 Mar 7;268(1466):525-9. doi: 10.1098/rspb.2000.1395.
The flowers of most angiosperm species are hermaphroditic. Spatial separation of male and female organs within a flower (hercogamy) is a common character traditionally interpreted as an adaptation to reduce intrafloral self-fertilization, one potential cost of hermaphroditism. Another possible cost that may lead to selection for hercogamy is physical interference between male and female floral functions. Here, I present evidence demonstrating the role of a floral character in reducing female interference with male function. The bi-lobed stigma of the bush monkeyflower closes after receiving pollen, causing increased spatial separation of the anthers and stigma ('movement' hercogamy). Experimental manipulations show that flowers with closed stigmas export more than twice as much pollen to other flowers as those in which the stigma is prevented from closing. However, stigma closure only minimally reduces the potential for intrafloral self-pollination. This study provides the first experimental evidence that selection to reduce intrafloral male female interference can be a strong selective force and can drive the evolution of floral characters usually interpreted as mechanisms to reduce self-fertilization.
大多数被子植物的花是两性花。花内雄性和雌性器官的空间分离（雌雄异位）是一个常见特征，传统上被解释为一种减少花内自花授粉的适应方式，而自花授粉是两性花的一个潜在代价。另一个可能导致对雌雄异位进行选择的代价是雄性和雌性功能之间的物理干扰。在此，我提供证据证明一种花部特征在减少雌性对雄性功能的干扰方面所起的作用。丛林猴面花的两裂柱头在接受花粉后会闭合，导致花药和柱头之间的空间分离增加（“移动”雌雄异位）。实验操作表明，柱头闭合的花向其他花输出的花粉量是阻止柱头闭合的花的两倍多。然而，柱头闭合仅略微降低了花内自花授粉的可能性。这项研究提供了首个实验证据，表明选择减少花内雄性与雌性之间的干扰可能是一种强大的选择力量，并且能够推动通常被解释为减少自花授粉机制的花部特征的进化。
