Dudash M R, Fenster C B
Department of Biology, H. J. Patterson Hall, University of Maryland, College Park, Maryland 20742 USA;
Am J Bot. 2001 Nov;88(11):1953-9.
The goal of this study was to understand the interaction among breeding system, mating system, and expression of inbreeding depression in the hermaphroditic, primarily hummingbird-pollinated, iteroparous, short-lived perennial Silene virginica. We performed hand-selfed and hand-outcrossed pollinations in the field, conducted detailed floral observations within individual flowers and plants, and assayed adult tissue from flowering plants for a genetic estimate of population outcrossing rate. We quantified the opportunity for geitonogamy as the proportion of days each plant exhibited simultaneous male and female function, i.e., asynchronous expression of male- and female-phased flowers. Expression of cumulative inbreeding depression based on germination rate and total flower production in the glasshouse was ∼40% and was congruent with the estimated high outcrossing rate of 0.89. Floral observations demonstrated strong temporal protandry within each flower (dichogamy) as well as complete spatial separation between male and female function within each flower (herkogamy). On average, 29% of the time there were both male- and female-phased flowers present on an individual plant. We conclude that our estimate of inbreeding depression is compatible with a largely outcrossing mating system and the amount of selfing observed, likely results from geitonogamy. This study illustrates the utility of examining both the causes and the consequences of inbreeding via selfing to provide additional insights into the evolution of plant mating systems.
本研究的目的是了解雌雄同体、主要由蜂鸟传粉、多年生、寿命较短且可多次结果的弗吉尼亚麦瓶草的繁殖系统、交配系统和近交衰退表达之间的相互作用。我们在田间进行了人工自花授粉和人工异花授粉，对单个花朵和植株进行了详细的花部观察，并对开花植株的成年组织进行了检测，以对种群杂交率进行遗传估计。我们将同株异花授粉的机会量化为每株植物同时展现雄花和雌花功能的天数比例，即雄花和雌花阶段异步表达。基于温室中发芽率和总花产量的累积近交衰退表达约为40%，与估计的0.89的高杂交率一致。花部观察表明，每朵花内存在强烈的时间上的雄性先熟（雌雄异熟）以及每朵花内雄花和雌花功能在空间上的完全分离（雌雄异位）。平均而言，单个植株上同时存在雄花和雌花阶段花朵的时间占29%。我们得出结论，我们对近交衰退的估计与主要异交的交配系统以及观察到的自交量相符，自交量可能源于同株异花授粉。这项研究说明了通过自交研究近交的原因和后果以深入了解植物交配系统进化的实用性。
