克隆植物的无性与有性繁殖对策

 许多植物同时具有克隆生长与有性繁殖，两种繁殖方式间的平衡在不同物种间以及同一物种内不同种群间变化很大。旺盛的克隆生长可能会从多方面影响生活史进化。首先， 许多克隆植物的有性繁殖与更新程度都很低，甚至有一些植物由于克隆生长而几乎完全放弃了有性过程，从而影响到克隆植物对局域环境的适应和地理范围进化。其次，克隆生长增大花展示进而增加了对传粉者的吸引，同时也增加了同株异花授粉的风险，而同株异花授粉往往会导致植物雄性和雌性适合度的下降。因此，克隆植物的空间结构与交配方式间可能存在着协同进化关系。最后，克隆生长与有性繁殖间可能存在着权衡关系：对克隆生长的资源 投入将会减少对有性繁殖的资源投入。这种权衡关系可能是由环境条件、竞争力度、植物寿 命和遗传等因素决定的。如果不同的繁殖方式是植物在不同环境下采取的适应性对策，那么我们可以预期：在波动和竞争力度大的生境中，植物应将大部分的繁殖资源分配给有性繁殖；而在相对稳定的环境中，克隆繁殖应该占据优势地位。但是自然选择对两种繁殖方式的选择结果是什么，以及控制这两种方式间平衡的生态和遗传因子究竟有哪些，到底是克隆生长单向地影响了植物的有性繁殖，还是与有性过程相伴随的选择压力同时塑造了植物的克隆习 性？目前尚不清楚。同时从无性与有性繁殖两个方面综合考察克隆植物的繁殖对策是今后 亟待加强的工作。

ASEXUAL AND SEXUAL REPRODUCTIVE STRATEGIES IN CLONAL PLANTS

Most plants can reproduce both sexually and vegetatively, and the balance between the two reproductive modes may vary widely between and within species. Extensive clonal growth may affect the evolution of life history traits in many ways. First, in some clonal species, sexual reproduction and recruitment are very low and drop to nil in extreme cases. Variation in sexual reproduction may strongly influence the adaptation to local environments and the evolution of the geographic range. Second, clonal growth can increase floral display, and thus pollinator attraction, while it may impose serious constraints and evolutionary challenges on plants through geitonogamy that may strongly influence pollen dispersal. Geitonogamous pollination can bring a fitness cost for the female and male function in both self-compatible and self-incompatible species. Some co-evolutionary interactions, therefore, may exist between the spatial structure and the mating behavior of clonal plants. Finally, a trade-off may exist between sexual reproduction and clonal growth. Resource allocation towards the two reproductive modes may depend on environmental conditions, competitive dominance, life span and genetic factors. If different reproductive modes are the adaptive strategies for plants in different environments, we can predict that most of the resources should be allocated towards sexual reproduction in habitats with fluctuating environmental conditions and strong competition, while clonal growth should be dominant in stable habitats. Yet we know little about the consequences of natural selection on the two reproductive modes and the underlying ecological and/or genetic factors that control the balance of the two reproductive modes. It is still unclear whether clonal growth unidirectionally determines sexual reproductive processes or whether the selection pressures arising from sexual reproductive processes leads to clonality. Few studies have investigated the reproductive strategies of clonal plants simultaneously both from sexual and asexual perspectives.