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鸭跖草异型雄蕊的适应意义研究

A Study on the Adaptive Significance of Heteranthery in Commelina Communis (Commelinaceae)

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【作者】 宋云澎

【导师】 唐璐璐

【作者基本信息】 中南大学, 生物学, 2014, 硕士

【摘要】 摘要:对于无花蜜虫媒传粉植物而言,花粉是访花者唯一的报酬。因此无花蜜花的花粉面临两难选择:作为报酬还是用于传粉?解决花粉这一难题的有效途径之一是异型雄蕊的出现,即花中出现两种以上的雄蕊形态。根据“雄蕊功能分化”假说,异型雄蕊可分为觅食型雄蕊和传粉型雄蕊两种类型,这在二型雄蕊物种中已经得到验证,但是在三型雄蕊物种中尚未给出直接证据。我们以拥有典型三型雄蕊的无花蜜植物鸭跖草为材料,在其自然居群中,对鸭跖草花部特征、开花情况、性配置以及自然访花等展开广泛调查,通过移除不同类型雄蕊进行访花者选择实验,以花粉移出和落置来度量雄性和雌性生殖成功并利用自主开发的微卫星分子标记(SSR)对居群的交配系统进行定量分析。鸭跖草花部雌蕊存在多态性,根据花柱长短和有无分为三种类型:长花柱型,短花柱型和无花柱型。长花柱型花开花幅度大,占居群开花总数的80%以上,其花柱长度的变异系数显著小于短花柱型花的,受到稳定的进化选择压力。P/O比是1031.0±194.1,暗示着混合交配系统的存在。自然访花观察结果显示淡脉隧蜂为鸭跖草自然居群的主要访花者,访问的花数分别占两个自然居群的77.5%和92.2%,但传粉效率的评价结果表明淡脉隧蜂并不是一个合理的访花者,存在花粉盗食现象。鸭跖草花部雄蕊也存在多态性,根据花丝长度不同,分为长(L)、中(M)、短(S)三种类型。体内花粉萌发实验表明来自M和L型雄蕊的花粉活力没有区别,然而访花者选择实验发现:S和M型雄蕊的移除都显著地降低了访花者的访花次数,但对柱头花粉落置量没有影响;L型雄蕊的移除导致了柱头上花粉落置量的减少,但对访花者的访花次数没有影响。结果表明不同类型雄蕊在传粉过程中的功能不同:S型雄蕊起欺骗性吸引访花者的作用;M型雄蕊拥有吸引访花者和提供报酬的双重功能,为觅食型雄蕊;L型雄蕊促进柱头花粉落置,为传粉型雄蕊,支持了“雄蕊功能分化”假说。然而L型雄蕊花药花粉的移出量并不受S和M型雄蕊移除的影响,表明花粉盗食现象干扰了传粉过程中的花粉散布。对两个鸭跖草自然居群交配系统分析显示多位点异交率分别为0.32±0.11和0.23±0.07,表明居群内以自交为主。因此,虽然鸭跖草的三型雄蕊存在功能分化,但是淡脉隧蜂的花粉盗食行为弱化了异型雄蕊的功能分工。图12幅,表8

【Abstract】 Abstract:In nectarless flower, pollen is the only reward for pollinators. Thus, it is an evolutionary dilemma for these plants that they need to protect their precious pollen from pollen feeder while maintaining enough attractiveness to pollinators. Heteranthery, the occurrence of two or more distinct types of stamens in the same flower, has been thought to reconcile the evolutionary conflict by allowing different stamens to specialize in ’pollinating’ and ’feeding’ functions, respectively.Here, floral traits, flower types, sexual allocation and natural pollination have been investigated in natural populations of Commelina communis, a trimorphic stamen species. we investigated the functions of three different types of stamens and analyzed the mating systems by SSR in natural populations.In flowers of C. communis, the pistil is polymorphic. According to the length of style, three types of style exist:long styled, short styled and none styled. Long styled flowers are bigger than short styled flowers, occurring most common among natural populations (more than80%). However, the coefficient of variation of style length for long styled flowers was less than short one, suggested long styled flowers were under a stablizing selection pressure. Our data also showed that the serious pollen theft rather than legitimate pollination occurred in the two populations, accounting for77.5%and92.2%of total flower visits, respectively.According to the length of filament, stamens in flower of C. com munis are also divided into three types:Long (L), Middle (M) and Short (S) typed stamen. No significant difference in pollen vigor between M-and L-typed anther in C. communis was found. To further examine the pollination roles of the three stamen types we manipulated flowers in the natural populations. We constructed experimental arrays including intact flower as control, L-anther removed flower, M-anther removed flower and S-anther removed flower to investigate pollinator preference and assess pollen deposition and pollen removal of each flower. S-and M-anther removed flowers received much fewer visitations but had no effect on pollen receipt. L-anther removed flowers received as many visits as intact flowers but received significantly fewer pollen grains. The two types of brightly yellow stamens separately functioned as ’deceptive food’ and ’feeding’ for the pollinators. However, the potential role of brown inconspicuous stamens in offering pollen for cross-pollination was disrupted by pollen thieves, significantly impairing pollen dispersal and deposition from the pollinating anthers in C. communis and decreasing the levels of outcrossing (tm=0.23~0.32) in wild populations. These findings indicated that contemporary pollen theft severely weakened the function of heteranthery in C. Communis. In this thesis, a total of12

  • 【网络出版投稿人】 中南大学
  • 【网络出版年期】2015年 03期
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