The factors Governing the Maintenance of Gynodioecy in Sidalcea oregana ssp. spicata (Malvaceae)

DOCTORATE DISSERTATION:Gynodioecious populations contain both hermaphrodite and female plants. This dimorphism results in an inequality in the potential genetic contributions of the sex morphs. Females can contribute genes only through ovules, whereas hermaphrodites can contribute through both pollen and ovules. Thus, females must experience a compensatory advantage to be maintained. This advantage could be realized through higher seed production or production of higher quality seeds. The focus of this dissertation research was to evaluate the factors that could be operating to maintain females in gynodioecious Sidalcea oregano ssp. spicata (Malvaceae) at Sagehen Creek Field Station, in the Sierra Nevadas. I investigated the importance of both pollination and resource allocation in determining patterns of seed production by the sex morphs. The sex morphs receive equivalent and sufficient levels of pollination but females produced 10 percent more seeds than hermaphrodites. The sex morphs allocated similar total amounts of resources to reproduction on a whole-plant basis but females allocated a greater proportion to seeds while hermaphrodites allocated proportionately more to flowers. To study the factors that influence seed and seeding quality in the greenhouse and in the field I used a breeding design which allowed me to separate the effects of maternal sex and inbreeding. After the first year of growth in the greenhouse a selfed hermaphrodites’ offspring had an expected cumulative fitness of only 74 percent that of an outcrossed offspring. When levels of out-crossing were equivalent, offspring of females were 91 percent more fit than progeny of hermaphrodites. It is unlikely that resource provisioning differences created this substantial fitness differential; seeds produced by the sex morphs did not differ significantly in biomass, nitrogen or phosphorus content. It is possible that this fitness differential was due to genetic (cytoplasmic) maternal effects. Under different conditions of resource availability, however, sex-specific resource allocation could result in provisioning differences that do affect fitness. I manipulated resource availability by adding NPK fertilizer to plants in the field. The sex morphs responded differently to these conditions in terms of flowering time, seed production, and per seed allocation. Hermaphrodites prioritized pollen allocation over seed allocation. Sex-specific allocation patterns can be interpreted as fitness optimizing strategies, and may play an important role in the maintenance of gynodioecy in Sidalcea, especially if resources vary.

博士学位论文：雌全异株（gynodioecy）种群同时包含两性株与雌株。该性别二态性会导致不同性别表型的潜在遗传贡献不均等：雌株仅能通过胚珠传递基因，而两性株可同时通过花粉与胚珠传递基因。因此，雌株必须获得补偿优势才能在种群中得以维持。此类补偿优势可通过更高的种子产量或更优质的种子生产得以实现。
本博士论文的研究核心为评估在内华达山脉赛亨溪野外站的穗状香葵（Sidalcea oregano ssp. spicata，锦葵科）雌全异株种群中，维持雌株存在的潜在作用因素。本研究探究了传粉与资源分配对两种性别表型种子产量格局的调控作用。结果显示，两种性别表型接收到的传粉水平相当且充足，但雌株的种子产量较两性株高出10%。整株水平上，两种性别表型的总繁殖资源投入相似，但雌株将更大比例的资源分配至种子生产，而两性株则将更多比例的资源分配至花朵发育。
为探究温室与野外环境中影响种子及实生苗质量的因素，本研究采用了可分离母本性别与近交效应的育种设计。温室种植第一年后，自交两性株的子代累积适合度仅为异交子代的74%。当异交水平一致时，雌株的子代适合度较两性株子代高出91%。资源供给差异不太可能造成这一显著的适合度差异：两种性别表型产生的种子在生物量、氮含量与磷含量上均无显著差异。该适合度差异可能源于遗传（细胞质）母本效应。然而，在不同的资源可获得性条件下，性别特异性的资源分配模式可能会产生影响适合度的资源供给差异。
本研究通过向野外植株施加氮磷钾（NPK）复合肥来调控资源可获得性，结果发现两种性别表型在开花时间、种子产量及单粒种子资源分配上对该处理的响应存在差异。两性株优先将资源分配至花粉生产而非种子生产。性别特异性的资源分配模式可被解读为适合度优化策略，且可能在雌全异株种群的维持中发挥重要作用，尤其当资源条件存在波动时。