Dorken Marcel E, Barrett Spencer C H
Department of Botany, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2.
Evolution. 2003 Sep;57(9):1973-88. doi: 10.1111/j.0014-3820.2003.tb00378.x.
The existence of monoecious and dioecious populations within plant species is rare. This limits opportunities to investigate the ecological mechanisms responsible for the evolution and maintenance of these contrasting sexual systems. In Sagittaria latifolia, an aquatic flowering plant, monoecious and dioecious populations exist in close geographic proximity but occupy distinct wetland habitats differing in the relative importance of disturbance and competition, respectively. Life-history theory predicts contrasting evolutionary responses to these environmental conditions. We propose that the maintenance of monoecy and dioecy in S. latifolia is governed by ecological selection of divergent life-history strategies in contrasting habitats. Here we evaluate this hypothesis by comparing components of growth and reproduction between monoecious and dioecious populations under four conditions: natural populations, a uniform glasshouse environment, a common garden in which monoecious and dioecious populations and their F1 progeny were compared, and a transplant experiment using shaded and unshaded plots in a freshwater marsh. Plants from dioecious populations were larger in size and produced heavier corms in comparison with monoecious populations. Monoecious populations flowered earlier and produced more flowers, clonal ramets, and corms than dioecious populations. The life-history differences between the sexual systems were shown to have a quantitative genetic basis, with F1 progeny generally exhibiting intermediate trait values. Survival was highest for each sexual system in field plots that most closely resembled the habitats in which monoecious (unshaded) and dioecious (shaded) populations grow. These results demonstrate that monoecious and dioecious populations exhibit contrasting patterns of investment in traits involved with growth and reproduction. Selection for divergent life histories between monoecious and dioecious populations of S. latifolia appears to be the principal mechanism maintaining the integrity of the two sexual systems in areas of geographic overlap.
在植物物种中，雌雄同株和雌雄异株种群的存在较为罕见。这限制了研究导致这些不同性系统进化和维持的生态机制的机会。在水生开花植物宽叶慈姑中，雌雄同株和雌雄异株种群在地理上紧密相邻，但分别占据不同的湿地生境，这些生境在干扰和竞争的相对重要性方面存在差异。生活史理论预测了对这些环境条件的不同进化反应。我们提出，宽叶慈姑中雌雄同株和雌雄异株的维持是由在不同生境中对不同生活史策略的生态选择所支配的。在这里，我们通过比较雌雄同株和雌雄异株种群在四种条件下的生长和繁殖组成部分来评估这一假设：自然种群、统一的温室环境、一个比较雌雄同株和雌雄异株种群及其F1后代的共同花园，以及在淡水沼泽中使用有阴影和无阴影地块的移植实验。与雌雄同株种群相比，雌雄异株种群的植株更大，球茎更重。雌雄同株种群比雌雄异株种群开花更早，产生更多的花、克隆分株和球茎。性系统之间的生活史差异显示具有数量遗传基础，F1后代通常表现出中间性状值。在与雌雄同株（无阴影）和雌雄异株（有阴影）种群生长的生境最相似的田间地块中，每个性系统的存活率最高。这些结果表明，雌雄同株和雌雄异株种群在与生长和繁殖相关的性状投资上表现出不同的模式。宽叶慈姑雌雄同株和雌雄异株种群之间对不同生活史的选择似乎是在地理重叠区域维持这两种性系统完整性的主要机制。
