Department of Biology, University of Washington, Seattle, Washington, 98195, USA.
Burke Museum of Natural History and Culture, Seattle, Washington, 98195, USA.
Am J Bot. 2024 Oct;111(10):e16406. doi: 10.1002/ajb2.16406. Epub 2024 Sep 18.
Seed dispersal is a critical process impacting individual plants and their communities. Plants have evolved numerous strategies and structures to disperse their seeds, but the evolutionary drivers of this diversity remain poorly understood in most lineages. We tested the hypothesis that the evolution of wind dispersal traits within the melicgrasses (Poaceae: Meliceae Link ex Endl.) was correlated with occupation of open and disturbed habitats.
To evaluate wind dispersal potential, we collected seed dispersal structures (diaspores) from 24 melicgrass species and measured falling velocity and estimated dispersal distances. Species' affinity for open and disturbed habitats were recorded using georeferenced occurrence records and land cover maps. To test whether habitat preference and dispersal traits were correlated, we used phylogenetically informed multilevel models.
Melicgrasses display several distinct morphologies associated with wind dispersal, suggesting likely convergence. Open habitat taxa had slower-falling diaspores, consistent with increased wind dispersal potential. However, their shorter stature meant that dispersal distances, at a given wind speed, were not higher than those of their forest-occupying relatives. Species with affinities for disturbed sites had slower-falling diaspores and greater wind dispersal distances, largely explained by lighter diaspores.
Our results are consistent with the hypothesized evolutionary relationship between habitat preference and dispersal strategy. However, phylogenetic inertia and other plant functions (e.g., water conservation) likely shaped dispersal trait evolution in melicgrasses. It remains unclear if dispersal trait changes were precipitated by or predated changing habitat preferences. Nevertheless, our study provides promising results and a framework for disentangling dispersal strategy evolution.
种子传播是影响个体植物及其群落的关键过程。植物已经进化出许多策略和结构来传播它们的种子，但在大多数谱系中，这种多样性的进化驱动因素仍知之甚少。我们检验了这样一个假设，即在麦草科（禾本科：Meliceae Link ex Endl.）内风传播特征的进化与开阔和干扰生境的占据有关。
为了评估风传播潜力，我们从 24 种麦草中收集了种子传播结构（胚珠），并测量了下落速度并估计了传播距离。使用地理参考的出现记录和土地覆盖图记录了物种对开阔和干扰生境的亲和力。为了测试栖息地偏好和传播特征是否相关，我们使用了基于系统发育的多层次模型。
麦草显示出几种与风传播相关的不同形态，这表明可能存在趋同进化。开阔生境类群的胚珠下落速度较慢，这与增加的风传播潜力一致。然而，它们的矮小身材意味着在给定风速下的传播距离并不高于其森林生境的亲缘关系。偏好干扰生境的物种具有下落速度较慢的胚珠和更大的风传播距离，这主要是由于胚珠较轻。
我们的结果与栖息地偏好与传播策略之间假设的进化关系一致。然而，系统发育惯性和其他植物功能（例如，水分保持）可能塑造了麦草中传播特征的进化。尚不清楚传播特征的变化是由栖息地偏好的变化引发的还是先于其发生的。尽管如此，我们的研究提供了有希望的结果，并为厘清传播策略进化提供了框架。
