Natural selection on floral traits: variation in agents and targets

花性状的自然选择：媒介和目标的变化

• 批准号: RGPIN-2014-05399
• 负责人: Worley, Anne
• 金额: $ 1.97万
• 依托单位: University of Manitoba
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611618
• 关键词: Natural; selection; floral; traits; variation

Flowers determine mating opportunities in animal-pollinated plants because pollinators transport male gametes (pollen) between flowers and plants. Pollinators form an essential “ecosystem service” in natural and agricultural ecosystems by ensuring fruit and seed production. As a result, natural selection by pollinators contributes to the tremendous diversity in wild flowers and inflorescences. Our understanding of floral evolution is still limited in several areas. These include: (1) selection through siring success, even though male parents contribute half the genes to each generation; (2) how selection affects floral traits when floral visitors are diverse; and (3) how often reproduction is limited by pollen receipt versus the availability of water, nutrients or other resources. My proposed research addresses these gaps. Polemonium brandegeei is a perennial herb pollinated by hummingbirds and hawkmoths, and visited by pollen consuming flies (pollen thieves). Our work to date indicates that the two pollinators exert contrasting natural selection on sex-organ position and flower width, suggesting that flower shape may be a compromise between the phenotype that is best under each pollinator. My lab will first conduct controlled experiments measuring how selection by each pollinator is modified by differences in flower number, a trait that varies widely in natural populations. Second, we will determine how pollen consumers affect siring potential of different flower shapes, and whether they limit the pollen available for seed set. Third, we will initiate long-term studies to quantify selection in natural populations. We will include estimates of siring success (paternity) based on genetic fingerprints. Supplementation of natural pollen receipt will distinguish selection by pollinators from selection caused by other factors such as nutrient limitation or drought. Lady’s slipper orchids (Cypripedium) trap insect visitors in their flowers rather than producing floral rewards to retain pollinators. I hypothesize that the small flowers and narrow pollination routes of endangered C. candidum contribute to low fruit set in northern populations because few insects are both small and strong enough to escape past the sex organs. Higher fruit set in widespread C. parviflorum and hybrids may reflect larger flowers and wider pollination routes. These differences in fruit set may affect gene transfer between species. First, I propose to extend our surveys of flower size, fruit set, and habitat quality across C. candidum’s range, compare pollinator communities in selected populations, and use genetic fingerprints to assess the direction of gene flow between species. Second, my lab will examine the direct effect of pollination route size on pollen movement; we will use plants from a C. parviflorum population, where flowers are comparable in size to either typical flowers of C. candidum (small) or C. parviflorum (larger) flowers, but do not differ in other traits such as flower colour or scent. These studies will advance my long-term goals of understanding how diverse floral visitors affect selection on floral design and display, and how floral phenotypes affect reproduction and mating patterns when flowers do not reward pollinators. They will also contribute to general evolutionary questions regarding the importance of variation in selection for the maintenance of genetic variation, evolution of specialized vs. generalized phenotypes, and gender conflict in selection. Findings will increase our understanding of evolution and ecological genetics, and will inform conservation biologists about strategies for preserving endangered species, and members of the public interested in evolution and natural history.

在动物授粉的植物中，花决定了交配的机会，因为传粉者在花和植物之间运输雄配子(花粉)。传粉者通过确保水果和种子的生产，在自然和农业生态系统中形成了一项基本的“生态系统服务”。因此，传粉者的自然选择促成了野生花卉和花序的巨大多样性。我们对花卉进化的了解在几个方面仍然有限。这些问题包括：(1)通过父本的成功选择，尽管父本为每一代贡献了一半的基因；(2)当访花的花卉多样化时，选择如何影响花的特征；以及(3)繁殖受到花粉接收与水、养分或其他资源的可用性的限制的频率。我提出的研究解决了这些差距。 Pleemonum brandgeei是一种多年生草本植物，由蜂鸟和天蛾授粉，并有捕食花粉的苍蝇(花粉窃贼)访问。到目前为止，我们的工作表明，这两种传粉者在性器官位置和花宽上进行了截然不同的自然选择，这表明花形可能是两种传粉者最好的表型之间的折衷。我的实验室将首先进行对照实验，测量每个传粉者的选择如何因花数的差异而改变，这一特征在自然种群中差异很大。其次，我们将确定花粉消费者如何影响不同花型的杂交潜力，以及它们是否限制了可用于结实的花粉。第三，我们将启动长期研究，量化自然种群中的选择。我们将包括基于遗传指纹的父系成功(父子关系)估计。补充天然花粉收获物将把授粉者的选择与营养限制或干旱等其他因素造成的选择区分开来。 淑女拖鞋兰花(塞浦路斯)在花中诱捕昆虫访客，而不是产生花卉奖励来留住传粉者。我推测，濒危的白花锦鸡儿的小花和狭窄的授粉路线是北方种群结实率低的原因之一，因为很少有昆虫既小又强壮，能够逃过性器官。在广布的小花锦鸡儿和杂交种中，较高的座果率可能反映了更大的花和更宽的授粉路线。这些坐果率的差异可能会影响物种间的基因转移。首先，我建议扩大我们对白花仙人掌的花朵大小、座果和栖息地质量的调查，比较选定种群中的传粉者群落，并使用遗传指纹来评估物种之间的基因流动方向。其次，我的实验室将研究授粉路线大小对花粉移动的直接影响；我们将使用来自小花锦鸡儿种群的植物，其中花的大小与白花锦鸡儿(小花)或小花锦鸡儿(大花)的典型花相似，但在花色或气味等其他特征上没有区别。 这些研究将推进我的长期目标，即了解不同的花卉访客如何影响花卉设计和展示的选择，以及当花不奖励传粉者时，花卉表型如何影响繁殖和交配模式。它们还将有助于解决一般的进化问题，如选择中变异对保持遗传变异的重要性，特殊表型与一般表型的进化，以及选择中的性别冲突。这些发现将增加我们对进化论和生态遗传学的理解，并将使保护生物学家了解保护濒危物种的策略，以及对进化论和自然历史感兴趣的公众成员。