Kay Kathleen M, Anderson Bruce
Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA 95060, USA.
Department of Botany and Zoology, Stellenbosch University, Matieland 7602, South Africa.
Ann Bot. 2025 Jul 31. doi: 10.1093/aob/mcaf096.
Floral diversity, a striking feature of angiosperm evolution, provides the impetus and rationale for linking pollinator-driven selection to speciation processes. Perhaps the most widely adopted model for pollinator-driven speciation is the Grant-Stebbins model, in which plant populations locally adapt to the most effective pollinator, leading to floral ecotype formation and, eventually, reproductive isolation and speciation. However, modelling and empirical studies suggest that populations need not adapt to the most effective pollinator, and major floral transitions remain poorly explained.
We evaluate the Grant-Stebbins model, focusing especially on the most effective pollinator principle. We use floral adaptive landscapes to articulate a more complete and accurate framework for understanding floral adaptation, starting with the premise that plants evolve to maximize fitness. We highlight ways to improve the assessment of pollinator fitness functions, both singly and in combination. We show how floral adaptive landscapes can be used to describe processes of floral adaptation within populations, evolutionary transitions between floral phenotypes, and a variety of real-world situations that do not fit neatly under the Grant-Stebbins model. Finally, we evaluate how floral adaptive landscapes can clarify the role of pollination in speciation under a variety of species concepts.
The Grant-Stebbins model, while inspiring decades of empirical studies, is a caricature of pollinator-driven speciation and explains only a limited range of adaptive outcomes. By using adaptive landscapes, we acknowledge that flowers are not adaptations to the most effective pollinator, but adaptations to maximize fitness, making evolutionary shifts between distinct floral phenotypes easier to understand in multi-pollinator environments. Finally, we argue that while pollinators often drive floral divergence, speciation most likely results from simultaneous divergence in multiple niche axes across a geographic range, which has been underemphasized in plant speciation research.
花的多样性是被子植物进化的一个显著特征，为将传粉者驱动的选择与物种形成过程联系起来提供了动力和理论依据。也许传粉者驱动物种形成最广泛采用的模型是格兰特 - 斯特宾斯模型，在该模型中，植物种群在当地适应最有效的传粉者，导致花生态型的形成，并最终导致生殖隔离和物种形成。然而，建模和实证研究表明，种群不一定需要适应最有效的传粉者，而主要的花的转变仍然难以解释。
我们评估格兰特 - 斯特宾斯模型，特别关注最有效传粉者原则。我们使用花的适应性景观来阐明一个更完整、准确的框架，以理解花的适应性，前提是植物进化以最大化适合度。我们强调了单独和组合改进传粉者适合度函数评估的方法。我们展示了花的适应性景观如何用于描述种群内花的适应过程、花表型之间的进化转变，以及各种不符合格兰特 - 斯特宾斯模型的现实世界情况。最后，我们评估花的适应性景观如何在各种物种概念下阐明传粉在物种形成中的作用。
格兰特 - 斯特宾斯模型虽然激发了数十年的实证研究，但却是传粉者驱动物种形成的一个简化描述，只解释了有限范围的适应性结果。通过使用适应性景观，我们认识到花不是对最有效传粉者的适应，而是对最大化适合度的适应，这使得在多传粉者环境中不同花表型之间的进化转变更容易理解。最后，我们认为虽然传粉者通常推动花的分化，但物种形成最有可能是由地理范围内多个生态位轴的同时分化导致的，这在植物物种形成研究中一直未得到充分重视。
