Abstract

Geographical variation in pollinator assemblages can result in divergent selective pressures and consequently drive the evolution of phenotypically distinct pollination ecotypes. Intraspecific divergence in pollination systems is well known among angiosperms, but is poorly studied among gymnosperms, often considered a relictual group not undergoing recent radiations. We investigated whether geographical divergence in the chemistry of volatiles emitted by cones of the cycad Encephalartos ghellinckii can be linked with functions for attracting different pollinators. We tested the pollination effectiveness of different insects in terms of deposition of fluorescent dye on micropyles and investigated whether daily fluctuations in cone temperature are correlated with insect pollinator activity. We also performed field bioassays to test the responses of insects to key volatiles and laboratory y-maze experiments to determine whether insects discriminate among cones of the two forms. Experiments confirmed that the beetles Metacucujus goodei and Erotylidae sp. nov. are the most effective pollinators of the mountain and lowland forms, respectively. A peak in cone temperatures in the afternoon was associated with extensive movement of insects among cones of mountain plants, but only limited movement of insects among cones of lowland plants. In field bioassays, Metacucujus goodei beetles were attracted mainly to (3E)-1,3-octadiene, a dominant component of the scent of mountain plants, whereas Erotylidae sp. nov. responded to camphene, a dominant component of the scent of lowland plants. When offered a choice, beetles preferred cones from the local population over those from a different population. The results suggest that E. ghellinckii consists of two pollination ecotypes with modifications in scent chemistry being correlated with an apparent shift between different pollinators. The relationship between thermogenesis and pollinator activities varies between ecotypes, with mountain plants showing a push–pull type of system and the lowland plants a system in which insects depart from cones with declining quality. This study highlights the role of insect pollinators in driving the evolution of cycads and the importance of thermogenesis and volatile emissions for mediating some beetle pollination systems.

中文翻译：

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非洲苏铁Encephalartos ghellinckii（Zamiaceae）授粉生态型的证据

摘要

传粉媒介组合的地理差异可能导致不同的选择压力，因此驱使表型上不同的授粉生态型进化。授粉系统中的种内差异在被子植物中是众所周知的，但是在裸子植物（通常被认为是未接受近期辐射的遗留群体）中的研究很少。我们调查了苏铁树脑锥的视锥细胞释放的挥发物的化学分布是否存在地理差异可以与吸引不同传粉媒介的功能联系起来。我们根据荧光染料在微粒上的沉积情况，测试了不同昆虫的授粉效果，并研究了锥孔温度的每日波动是否与昆虫授粉活动相关。我们还进行了现场生物测定，以测试昆虫对关键挥发物的反应，并进行实验室y迷宫实验，以确定昆虫是否区分这两种形式的圆锥体。实验证实甲虫Metacucujus goodei和Erotylidae sp。十一月 分别是山区和低地形式最有效的传粉媒介。下午锥体温度的峰值与昆虫在高山植物的锥体之间的广泛运动有关，但与昆虫在低地植物的锥体之间的有限运动有关。在野外生物测定中，古葫芦甲虫主要被（3 E）-1,3-辛二烯吸引，这是山地植物气味的主要成分，而Erotylidae sp。十一月 樟脑是低地植物气味的主要组成部分。当提供选择时，甲虫会优先选择本地种群的圆锥体，而不是其他种群的圆锥体。结果表明，E。ghellinckii由两种授粉生态型组成，它们的气味化学性质与不同授粉媒介之间的明显转变有关。生热与传粉媒介活动之间的关系在不同的生态类型之间有所不同，山地植物表现出推拉型系统，而低地植物表现出昆虫从质量下降的视锥中脱离的系统。这项研究突出了昆虫授粉媒介在推动苏铁进化过程中的作用，以及生热和挥发性排放物对介导某些甲虫授粉系统的重要性。