Department of Ecology and Evolutionary Biology and the Peabody Museum of Natural History, Yale University, P.O. Box 208105, New Haven, Connecticut 06511, USA
Am Nat. 2006 Jun;167(6):777-93. doi: 10.1086/504605. Epub 2006 Apr 28.
The cactus life-form is cited as an example of a tight relationship between organism form and function: a succulent, long-lived, photosynthetic stem allows cacti to survive long periods of drought while maintaining a positive tissue water status. Pereskia (Cactaceae) comprises 17 species of leafy shrubs and trees that are thought to represent the original cactus condition. Recent phylogenetic work has shown that there are two separate clades of Pereskia species, which are basal and paraphyletic with respect to the rest of the cacti. We selected seven Pereskia species, representing both clades, and characterized their water relations by measuring a suite of physiological traits in wild populations. Additionally, we estimated basic climate parameters from collection localities for all 17 Pereskia species. Extant Pereskia species exhibit ecological water use patterns that are very similar to those of the leafless, stem-succulent cacti. Ancestral trait reconstruction for the physiological and environmental data provides a preliminary assessment of the ecology and water relations of the earliest cacti and suggests that several key elements of the cactus ecological niche were established before the evolution of the cactus life-form. We interpret these ecological traits as potentially important drivers of evolutionary innovation in the cacti.
肉质、长寿、光合作用的茎使仙人掌能够在长时间干旱的情况下生存，同时保持组织水分的积极状态。Pereskia（仙人掌科）由 17 种多叶灌木和乔木组成，被认为代表了原始仙人掌的形态。最近的系统发育研究表明，Pereskia 物种有两个独立的分支，相对于其他仙人掌来说是基础的和并系的。我们选择了 7 种代表两个分支的 Pereskia 物种，通过测量野生种群的一系列生理特征来描述它们的水分关系。此外，我们还根据所有 17 种 Pereskia 物种的采集地点估计了基本的气候参数。现存的 Pereskia 物种表现出的生态用水模式与无叶、茎肉质的仙人掌非常相似。生理和环境数据的祖先特征重建为最早的仙人掌的生态和水分关系提供了初步评估，并表明在仙人掌生活形态进化之前，仙人掌生态位的几个关键要素已经建立。我们将这些生态特征解释为仙人掌进化创新的潜在重要驱动因素。
