Department of Biology, Amherst College, Amherst, Massachusetts 01002 USA;
Am J Bot. 2002 Dec;89(12):1907-15. doi: 10.3732/ajb.89.12.1907.
Populations of three North American species of Lycium (Solanaceae) are morphologically gynodioecious and consist of male-sterile (i.e., female) and hermaphroditic plants. Marked individuals were consistent in sexual expression across years and male sterility was present throughout much of the species' ranges. Controlled pollinations reveal that L. californicum, L. exsertum, and L. fremontii are functionally dioecious. Fruit production in females ranged from 36 to 63%, whereas hermaphrodites functioned essentially as males. Though hermaphrodites were mostly male, investigation of pollen tube growth reveals that hermaphrodites of all dimorphic species were self-compatible. Self-fertilization and consequent inbreeding depression are commonly invoked as important selective forces promoting the invasion of male-sterile mutants into cosexual populations. A corollary prediction of these models is that gender dimorphism evolves from self-compatible ancestors. However, fruit production, seed production, and pollen tube number following outcross pollination were significantly higher than following self-pollination for three diploid, cosexual species that are closely related to the dimorphic species. The data presented here on incompatibility systems are consistent with the hypothesis that polyploidy disrupted the self-incompatibility system in the gynodioecious species leading to the evolution of gender dimorphism.
三种北美枸杞属（茄科）植物的种群在形态上为雌雄异株，由雄性不育（即雌性）和两性植株组成。具有明显特征的个体在多年间的性表现上保持一致，雄性不育现象在这些物种的大部分分布范围内存在。控制性授粉揭示，加利福尼亚枸杞、外生枸杞和弗雷斯诺枸杞在功能上是雌雄异株的。雌性的果实产量范围为 36%至 63%，而两性植株基本上起到雄性的作用。尽管两性植株大多为雄性，但对花粉管生长的研究表明，所有二态性物种的两性植株都是自交亲和的。自交和随之而来的近交衰退通常被认为是促进雄性不育突变体侵入雌雄同体种群的重要选择力量。这些模型的一个推论是，性别二态性是从自交亲和的祖先进化而来的。然而，对于三个与二态性物种密切相关的二倍体、雌雄同体物种，异交授粉后的果实产量、种子产量和花粉管数量明显高于自交授粉后的产量。这里提出的关于不亲和系统的数据与多倍体破坏了雌雄异株物种中的自交不亲和系统，从而导致性别二态性进化的假说一致。
