澜沧舞花姜繁殖生物学特性及其进化意义探讨

REPRODUCTIVE CHARACTERISTICS OF GLOBBA LANCANGENSIS AND THEIR EVOLUTIONARY IMPLICATIONS

舞花姜属(Globba)植物具有多样的繁殖策略。分布于西双版纳的澜沧舞花姜(Globbalancangensis)自然条件下既能结实,同时又能在花序下部产生珠芽。通过对澜沧舞花姜的花部性状、花粉活力、传粉昆虫的访花行为、结实状况、珠芽产量等多方面的观测,初步了解了澜沧舞花姜的繁殖生物学特性。结果表明,澜沧舞花姜具有雄花及两性花同株的性表达特征。雄花及两性花的花粉在中午 12∶0 0以前活力很高,之后雄花的花粉活力急剧下降,而两性花的花粉到 16∶0 0仍有萌发能力。澜沧舞花姜在花序上产生雄花及两性花,每个花序每天仅开少量的花,其中 5 0 %的时间仅开雄花或两性花,在整个种群中形成了一定程度的暂时性的雄花两性花异株现象,从而增加了异交的可能性。澜沧舞花姜雄花的存在为P/O低的两性花提供了花粉补贴,这使得它可以通过调节雄花与两性花比例来调节种群的P/O,从而保证一定的结实能力。人工自交与异交下结果率没有差异,但自交结实率显著低于异交结实率,表明澜沧舞花姜有明显的自交不亲和现象。排蜂(Megapisdorstata)和黄绿彩带蜂(Nomiastrigata)是澜沧舞花姜的主要访花昆虫,其中排蜂是它的有效传粉昆虫。

Andromonoecy, i.e. presence of both male and bisexual (hermaphroditic) flowers on the same individuals of a species, is quite common in both wind- and animal-pollinated seed plants, while its ecological and evolutionary implications are still not fairly understood. In this paper we demonstrate an andromonoecious mating system in a native perennial herb, Globba lancangensis (Zingiberaceae), found in Xishuangbanna, SW China. Firstly, we describe the floral biology of this species: pollen viabilities, fruit-set ratios, behaviors of visiting insects and so forth, and then compare the morphological differences between male and hermaphroditic flowers. Secondly, we present the results of experiments designed to determine its breeding system, and to test whether this system has a self-incompatibility mechanism. Thirdly, we show the variations of sexual expression in this species with emphasis on the change of male : hermaphrodite ratios. Finally, we discuss the ecological and evolutionary implications of the variations in reproductive characteristics. Male and hermaphroditic flowers differed in several dimensions. Hermaphroditic flowers have significantly larger ovaries, longer corolla tubes, marginally wider staminodes and longer labellums. Hermaphroditic flowers have 48.4±12.2 (n=32) ovules in each ovary while male flowers have almost no viable ovules in their much smaller ovaries. Male flowers have 1 372±312 (n=32) pollen grains per anther, which is marginally more than that in hermaphroditic flowers with 1 099±346 (n=32). Male flowers also have a significantly longer anther appendage than hermaphroditic flowers. In natural populations, both male and hermaphroditic flowers open at 2∶30-3∶00 and the anthers dehisce at 5∶30-6∶00. There is no significant difference between male and hermaphroditic flowers in flower-opening and anther-dehiscing time. However, the male flowers shed at 13∶30-14∶00 while hermaphroditic flowers may stay until 4∶00 next morning. The pollen viabilities of hermaphrodite flowers were higher until 16∶00 in contrast to male flowers whose pollen viabilities decreased abruptly after noon. A ramet may present either a single male or a single hermaphrodite flower for many days during flowering, making itself temporally androdioecious, and may thus promote outcrossing. The existence of male flowers may offer offsets of pollen for the perfect flowers, which have relatively low P/O ratios (23±7, n=32). Thus, G. lancangensis may achieve its seed set by regulating the ratios of male to hermaphroditic flowers in community. There were no significant differences in fruit-set ratios between hand-selfing (17.2% or 17.7%) and hand-crossing (16.4% or 15.3%) but significant differences in seed-set ratios (seed/ovule ratios) were seen (5.71% or 6.89% vs. 42.76% or 42.99%), which suggested that this plant might maintain the mechanism of self-incompatibility. In contrast to previous reports that butterflies were visitors for Globba, two species of bees, Megapis dorstata and Nomia strigata, are the main visitors for G. lancangensis, while the former is the effective pollinator. G. lancangensis may encourage out-crossing by means of both andromonoecy and self-incompatibility.