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: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=710751
• 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。