Effect of multilevel selection on the evolution of gynodioecy

多级选择对雌雄异株进化的影响

• 批准号: RGPIN-2018-04698
• 负责人: Caruso, Christina
• 金额: $ 2.4万
• 依托单位: University of Guelph
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=757619
• 关键词: Effect; multilevel; selection; evolution; gynodioecy

Most traits are thought to evolve because they increase an individual's survival and reproduction. However, there are some traits that appear to decrease an individual's fitness, yet still evolve repeatedly. One such trait is gynodioecy, a type of sexual polymorphism in which hermaphroditic and female plants coexist within a population. Females have an inherent fitness disadvantage because they can reproduce only via seeds, whereas hermaphrodites can reproduce via both seeds and pollen. Despite this disadvantage, females, and thus gynodioecy, have evolved repeatedly in the flowering plants. Females could evolve in response to individual-level selection that acts only under a restricted set of conditions, or in response to selection at levels above and/or below the individual, including the group and the gamete. Measuring selection at multiple levels is important because traits evolve differently based on the level at which selection acts: even when the strength and direction of selection are similar across levels, both the causes of and responses to selection can differ.Our long-term goal is to determine how the evolution of gynodioecy has been affected by selection at multiple levels. Our recent work suggests that gynodioecy can evolve in response to frequency-dependent selection (where an individual's fitness depends in part on the mean phenotype of its group) and gametic selection (where the viability of a gamete depends on which allele it carries). However, we also found that the frequency of females varies widely among gynodioecious populations, suggesting that the strength of selection varies. To determine the why the strength of selection varies among gynodioecious populations, we will focus on two short-term goals. First, we will identify the mechanisms that cause frequency-dependent selection on female plants by testing why females have frequency-dependent fitness and whether the strength of frequency-dependent selection depends on conspecific density. Second, we will identify the mechanisms that cause gametic selection on sex-determining genes by testing whether variation in the strength of gametic selection is caused by ecological or genetic factors and whether these genetic factors are in the cytoplasmic or nuclear genome. All of this work will be done in the gynodioecious species Lobelia siphilitica. Although gynodioecy was first studied by Darwin, there is still uncertainty as to why it evolves in some populations but not in others. The proposed research, by focusing on the mechanisms that cause frequency-dependent selection and gametic selection, will allow us to predict the ecological and genetic contexts in which gynodioecy is more and less likely to evolve. More generally, the proposed research will demonstrate how measuring selection at multiple levels can lead to new explanations for the repeated evolution of traits that appear to decrease an individual's fitness.

大多数特征被认为是进化的，因为它们增加了个体的生存和繁殖。然而，有一些特征似乎会降低个体的适应性，但仍然会反复进化。其中一种特征是雌性异构体，这是一种两性多态，即雌雄同体植物和雌性植物在一个种群中共存。雌性具有固有的适应性劣势，因为它们只能通过种子繁殖，而雌雄同体可以通过种子和花粉繁殖。尽管有这样的缺点，雌性和雌蕊异构体在开花植物中反复进化。雌性的进化可能是为了应对只在有限条件下发生的个体层面的选择，也可能是为了应对高于或低于个体层面的选择，包括群体和配子。在多个层次上测量选择是很重要的，因为特征的进化是基于选择发生作用的层次而不同的：即使选择的强度和方向在各个层次上是相似的，选择的原因和对选择的反应也可能不同。我们的长期目标是确定在多个层面上的选择是如何影响雌单核细胞的进化的。我们最近的研究表明，雌同体可以在频率依赖选择（个体的适应性部分取决于其群体的平均表型）和配子选择（配子的生存能力取决于它携带的等位基因）的反应中进化。然而，我们也发现雌性的频率在雌雄异株种群中差异很大，这表明选择的强度是不同的。为了确定为什么雌蕊异株种群的选择强度不同，我们将关注两个短期目标。首先，我们将通过测试为什么雌性具有频率依赖适应度以及频率依赖选择的强度是否取决于同种密度来确定导致雌性植物频率依赖选择的机制。其次，我们将通过测试配子选择强度的变化是由生态因素还是遗传因素引起的，以及这些遗传因素是在细胞质基因组还是核基因组中引起的，来确定导致性别决定基因配子选择的机制。所有这些工作将在雌蕊异株的半边莲（Lobelia siphilitica）中进行。虽然雌蕊异体最早是由达尔文研究的，但仍然不确定为什么它在一些人群中进化而在另一些人群中没有。通过关注频率依赖选择和配子选择的机制，我们可以预测雌蕊异体进化的生态和遗传背景。更一般地说，拟议的研究将证明如何在多个层面上衡量选择，可以为似乎降低个体适应性的特征的重复进化提供新的解释。