目的:已知叶性状是植物性能的有力预测因子,并且可以预期(co)随环境梯度变化。我们调查了变异,一体化,环境关系,和咖啡属叶片功能性状的进化史,通常是雨林林下的灌木,横跨非洲。更好地了解叶片性状进化中涉及的适应过程可以为在气候变化中使用和保护咖啡遗传资源提供信息。
方法:我们使用系统发育比较方法研究了从58种非洲咖啡物种的植物标本室标本中测量的六个叶片性状的进化。我们添加了环境数据和每个物种的最大植物高度数据,以测试各种(子)进化枝的性状-环境相关性,我们比较了连续性状进化模型,以识别驱动性状多样化的变量。
结果:在非洲的咖啡属中发现了大量的叶片性状变异,主要是种间的。在这些特征中,气孔大小和气孔密度表现出明显的权衡。我们在早期分支谱系中观察到低密度的大气孔,在最近的分类单元中观察到较高密度的小气孔。我们假设这与自从上世纪中期以来二氧化碳水平的下降有关。所有特征的布朗运动进化都被拒绝支持白噪声或Ornstein-Uhlenbeck模型,暗示这些特征具有适应性意义,而不是由纯粹的漂移驱动。叶面积的演变可能是由降水驱动的,在整个属的干燥气候中,叶子较小。
结论:一般来说,咖啡叶性状似乎在进化上不稳定,并受稳定选择的支配,尽管进化模式和相关性因考虑的特征和进化枝而异。我们的研究强调了在研究相关分类群的特征关系时,系统发育观点的重要性,以及各种分类范围的考虑。
OBJECTIVE: Leaf traits are known to be strong predictors of plant performance and can be expected to (co)vary along environmental gradients. We investigated the variation, integration, environmental relationships, and evolutionary history of leaf functional traits in the genus Coffea L., typically a rainforest understory shrub, across Africa. A better understanding of the adaptive processes involved in leaf trait evolution can inform the use and conservation of coffee genetic resources in a changing climate.
METHODS: We used phylogenetic comparative methods to investigate the evolution of six leaf traits measured from herbarium specimens of 58 African Coffea species. We added environmental data and data on maximum plant height for each species to test trait-environment correlations in various (sub)clades, and we compared continuous trait evolution models to identify variables driving trait diversification.
RESULTS: A substantial leaf trait variation was detected across the genus Coffea in Africa, which was mostly interspecific. Of these traits, stomatal size and stomatal density exhibited a clear trade-off. We observed low densities of large
stomata in early branching lineages and higher densities of smaller
stomata in more recent taxa, which we hypothesise to be related to declining CO2 levels since the mid-Miocene. Brownian Motion evolution was rejected in favour of White Noise or Ornstein-Uhlenbeck models for all traits, implying these traits are adaptively significant rather than driven by pure drift. The evolution of leaf area was likely driven by precipitation, with smaller leaves in dryer climates across the genus.
CONCLUSIONS: Generally, Coffea leaf traits appear to be evolutionarily labile and governed by stabilising selection, though evolutionary patterns and correlations differ depending on the traits and clades considered. Our study highlights the importance of a phylogenetic perspective when studying trait relationships across related taxa, as well as the consideration of various taxonomic ranges.