Inbreeding Depression and Selfing Rates in Hermaphroditic Species of Schiedea (Caryophyllaceae): A Comparison to Diclinous Species

与大多数动物不同的是，植物有不同的雄性和雌性个体，植物在繁殖系统中表现出很大的范围。大多数植物是两性的，在同一朵花中具有雄花和雌花的功能，但许多其他物种，包括一些重要的农作物，在同一植物上有不同的雄花和雌花，或由不同的雄株和雌株组成的种群(雌雄异株)。为了解释植物繁殖系统的多样性和雌雄异株的进化，人们提出了许多不同的假说。一个主要的论点表明，雌雄异体的进化是为了避免近亲繁殖的衰退。近亲繁殖抑制发生在近亲交配时，由此产生的后代活力和繁殖能力下降。如果近亲交配抑制是一个因素，那么人们应该预料到，在进化雌雄异株的种群中，既会发生高水平的近交自花授粉，也会出现高水平的近交抑制。虽然已经提出了许多理论，但关于这个问题的实证数据很少。我们正在研究近亲繁殖衰退在夏威夷植物Schiedea属雌雄异株进化中的作用。这一群体显然正在进化雌雄异株，并在非常接近的物种中展示了一系列繁殖系统。这项研究特别紧迫，因为由于栖息地破坏、草食动物引入的放牧以及与引进植物的竞争，来自脆弱的夏威夷生态系统的许多重要中间物种正濒临灭绝。有关促进植物育种系统变化的因素的知识对农业和林业中的实际问题具有许多潜在的育种应用。众所周知，近亲繁殖衰退会影响许多重要经济作物的产量，例如玉米。了解导致雌雄异株的因素可能会导致更大的能力来操纵植物的性别比例，在产量取决于雌性果实或种子生产的地方具有巨大的价值，就像许多作物物种的情况一样。了解单性繁殖的基础在杂交品系的生产中也很重要，因为雌性个体很容易杂交，而不需要耗时而昂贵的两性花去雄。

Unlike most animals which have individuals with separate male and female sexes, plants exhibit a great range in breeding systems. Most plant species are hermaphroditic with male and female function in the same flower, but many other species, including a number of important crop plants, have separate male and female flowers on the same plant or consist of populations of separate male and female plants (dioecy). Many different hypotheses have been proposed to explain the diversity of breeding systems in plants and the evolution of dioecy. One major argument suggests that dioecy has evolved to avoid inbreeding depression. Inbreeding depression occurs when closely related individuals mate and the resulting offspring show reduced vigor and ability to reproduce. If inbreeding depression is a factor, then one should expect to find both high levels of inbreeding self-pollination occurring as well as high levels of inbreeding depression in populations that are evolving dioecy. Although there have been many theories proposed, very little empirical data on this question is available. We are examining the role of inbreeding depression in the evolution of dioecy in the Hawaiian plant genus Schiedea. This group is apparently evolving dioecy and exhibits a range of breeding systems in very closely related species. This research is of special urgency because many important intermediate species from the fragile Hawaiian ecosystems are near extinction because of habitat destruction, grazing introduced by herbivores and competition with introduced plants. Knowledge of factors promoting changes in plant breeding systems has many potential breeding applications to practical problems in agriculture and forestry. Inbreeding depression is well known to influence yield in many economically important crop plants, such as corn. Knowledge of factors causing dioecy may lead to greater ability to manipulate sex ratios in plants and is of tremendous value where yield depends upon the production of fruit or seed by the females as is the case of many crop species. Understanding the basis of unisexaulity will also be important in production of hybrid strains, since female individuals are easily hybridized without the necessity of time-consuming costly emasculation of hermaphroditic flowers.