Natural selection on floral traits: variation in agents and targets

花决定了动物授粉植物的交配机会，因为传粉者在花和植物之间运输雄配子（花粉）。传粉媒介通过确保水果和种子的生产，形成自然和农业生态系统中必不可少的“生态系统服务”。 因此，传粉者的自然选择促成了野花和花序的巨大多样性。我们对花卉进化的理解在几个领域仍然有限。其中包括：（1）通过繁衍成功进行选择，尽管父本为每一代贡献了一半的基因； （2）当花卉访客多样化时，选择如何影响花卉性状； (3) 繁殖受到花粉接收与水、养分或其他资源可用性的限制的频率。我提出的研究解决了这些差距。 Polemium Brandegeei 是一种多年生草本植物，由蜂鸟和天蛾授粉，并受到花粉苍蝇（花粉窃贼）的拜访。迄今为止，我们的工作表明，两种传粉媒介在性器官位置和花宽度上发挥了对比的自然选择，这表明花形状可能是每种传粉媒介的最佳表型之间的折衷。我的实验室将首先进行对照实验，测量花朵数量的差异如何改变每种传粉媒介的选择，而花朵数量的差异在自然群体中差异很大。其次，我们将确定花粉消费者如何影响不同花朵形状的发芽潜力，以及它们是否限制了可用于结籽的花粉。第三，我们将启动长期研究来量化自然种群的选择。我们将包括基于遗传指纹的繁殖成功（亲子鉴定）的估计。补充天然花粉接收将区分传粉媒介的选择与其他因素（例如营养限制或干旱）引起的选择。 拖鞋兰（Cypripedium）将昆虫访客困在花朵中，而不是产生花朵奖励来留住传粉者。我推测，濒临灭绝的C. candidum 的小花和狭窄的授粉路线导致了北方种群的坐果率低，因为很少有昆虫既小又强，足以通过性器官逃脱。广泛分布的 C. parviflorum 和杂交种的较高坐果率可能反映了较大的花朵和较宽的授粉途径。坐果的这些差异可能会影响物种之间的基因转移。首先，我建议将我们对花的大小、坐果和栖息地质量的调查扩展到整个白花梨的范围，比较选定种群中的传粉昆虫群落，并使用遗传指纹来评估物种之间基因流动的方向。其次，我的实验室将研究授粉路线大小对花粉运动的直接影响；我们将使用来自 C. parviflorum 种群的植物，其中花朵的大小与 C. candidum（小）或 C. parviflorum（较大）花的典型花朵相当，但在其他性状（例如花颜色或气味）方面没有差异。 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，以及当花朵不奖励传粉者时花卉表型如何影响繁殖和交配模式。他们还将有助于解决一般进化问题，例如选择变异对于维持遗传变异的重要性、特殊表型与通用表型的进化以及选择中的性别冲突。研究结果将增加我们对进化和生态遗传学的理解，并将告知保护生物学家有关保护濒危物种的策略，以及对进化和自然历史感兴趣的公众。

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.