Cost-Benefits Tradeoffs Associated with Dimorphism in a Dioecious Plant

9629774德尔夫一些开花植物有分开的雄株和雌株，被称为雌雄异株。除了在主要功能上的不同(雄性产生花粉，而雌性产生种子)，雄性和雌性在其他特征(例如，花瓣或叶的大小、繁殖频率和生理特征)上经常表现出性别二型性。作为结实的结果，大多数雌雄异株物种的雌性在生殖方面比雄性投入更多的生物量。女性的这种更高的生殖努力应该意味着女性在其他结构上的投资将比男性少。因此，她们的“生殖成本”应该比男性高；即，女性往往表现出相对较慢的生长速度和/或较高的死亡率。研究人员计划研究雌雄异株植物--宽叶银莲花，这种植物似乎不符合雌性繁殖成本较高的模式。在这一物种中，男性的营养生长较少，死亡年龄比女性更早，尽管这一物种的雌性确实在生殖结构上投入了相对更多的生物量。此外，在这个物种中，雄花比雌花多10到15倍，雄花相对较小。研究人员将验证这样一种假设，即生产许多小花会给雄性带来很高的生殖成本，而且这一成本不能简单地通过测量投资于生殖结构的生物量(即碳)来预测，因为性别之间也可能存在生理差异。研究人员将通过两种方式检验这一假设：1)通过在普通花园和温室种植已知亲缘关系的植物，观察形态和生理性状的变化是否基于遗传并与花数相关，并观察相对寿命；2)进行人工选择实验，以缩小两性之间存在的花大小和花数的差异，并观察某些被认为对繁殖成本负责的生理性状(如呼吸频率)是否也随着形态性状的变化而变化。这将是第一次在植物中对一些动物报告的现象进行测试：性选择(为了获得多个配偶而进行的选择)会给雄性带来生存成本。此外，拟议的研究将有助于我们理解植物中性别二型性的进化。

9629774 Delph Some flowering plant species have separate male and female individuals and are termed dioecious. In addition to differing in their primary function (males produce pollen, whereas females produce seeds), males and females often exhibit sexual dimorphism in other traits (e.g., petal or leaf size, frequency of reproduction, and physiological traits). As a consequence of producing fruit, females of most dioecious species invest more biomass in reproduction than do males. This higher reproductive effort by females should mean that females will invest less in other structures than do males. Consequently, they should have a higher "cost of reproduction" than males; i.e., females often exhibit relatively slower rates of growth and/or higher rates of mortality. The investigators plan to study the dioecious plant, Silene latifolia, which does not appear to fit the pattern of females having a higher cost of reproduction. In this species, males grow less vegetatively and die at a younger age than females, even though females of this species do invest relatively more biomass in reproductive structures. In addition, in this species males produce 10 to 15 times more flowers than females, and male flowers are relatively small. The investigators will test the hypothesis that production of many, small flowers imposes a high cost of reproduction for the males, and that this cost can not be predicted simply by measuring biomass (i.e., carbon) invested in reproductive structures, because physiological differences between the sexes may also exist. The investigators will test this hypothesis in two ways: 1) by growing plants of known parentage in a common garden and greenhouse to observe whether variation in morphological and physiological traits is genetically based and correlated with flower number, and to observe relative longevity, and 2) by conducting an artificial selection experiment to reduce the magnitude of differences in flower size and number that exist between the sexes and obse rve whether certain physiological traits thought to be responsible for the cost of reproduction (such as respiration rate) also change with the change in the morphological traits. This will be the first test in plants of a phenomenon that has been reported for some animals: that sexual selection (selection for obtaining many mates) imposes a survival cost on males. Furthermore, the proposed research will contribute to our understanding of the evolution of sexual dimorphism in plants.