Data from: Mating consequences of contrasting hermaphroditic plant sexual systems

For hermaphroditic angiosperms with multiple flowers the sex roles can be exclusively combined in bisexual flowers (monocliny), strictly separated among different flowers (monoecy), or arrayed in mixtures of bisexual flowers with female flowers (gynomonoecy) or male flowers (andromonoecy). The hypothesized benefits favoring the evolution of these contrasting hermaphroditic sexual systems are typically examined individually, usually by assessing success through only one sex role. We tested predictions of most hypotheses experimentally with an andromonoecious species, Anticlea occidentalis (Melanthiaceae), based on the performance of intact plants (andromonoecy) and those with emasculated bisexual flowers (functionally monoecious) or emasculated male flowers (functionally monoclinous with sterile peripheral flowers). Andromonoecy in this species enables efficient, size-dependent resource allocation, emphasizing female function in large plants. Emasculation revealed that anthers in male flowers promote female mating quality (outcrossing rate and mate diversity), whereas anthers in bisexual flowers promote male mating quantity (pollen dispersal distance and probability of any siring success). Thus, different hermaphroditic sexual systems likely evolve to capitalize on suites of benefits, rather than just one, and provide compromises between quantitative and qualitative reproductive components. These compromises apparently maximize an individual’s combined genetic contributions through female and male functions, rather than separate contributions through each sex role.

对于具有多花的两性花被子植物而言，其性角色可分为三类：仅在两性花中同时兼具雌雄功能（雌雄同花（monocliny））、在不同花间严格分离雌雄功能（雌雄同株异花（monoecy）），或是以两性花与雌花（雌全同株（gynomonoecy））或雄花（雄全同株（andromonoecy））混合的形式存在。以往针对这些差异化的两性生殖系统演化的假说优势，通常仅单独开展检验，且往往仅通过单一性角色的繁殖成功情况进行评估。我们以雄全同株物种西方棋盘花（Anticlea occidentalis，黑药花科Melanthiaceae）为实验材料，基于完整植株（保持雄全同株状态）、去雄两性花植株（功能上为雌雄同株异花）以及去雄雄花植株（功能上为雌雄同花，仅外围花不育）的繁殖表现，对多数假说的预测进行了实验验证。该物种的雄全同株特性可实现基于植株大小的高效资源分配，在大型植株中更侧重雌性繁殖功能。去雄实验结果显示，雄花中的花药可提升雌性交配质量（异交率与配偶多样性），而两性花中的花药则可提升雄性交配数量（花粉传播距离与任意一次父本成功的概率）。由此可见，不同的两性生殖系统的演化，更可能是为了利用多重优势而非单一优势，并在繁殖数量与繁殖质量两类生殖组分之间达成权衡。这类权衡显然是为了通过雌雄双重功能最大化个体的综合遗传贡献，而非通过单一性角色分别实现独立的遗传贡献。