Data from: Beyond climate: convergence in fast evolving sclerophylls in Cape and Australian Rhamnaceae predates the mediterranean climate

Morphological convergence in mediterranean-type ecosystems (MTEs) has long been interpreted as adaptation to climatic similarities among the five MTEs of the world. Here, we challenge this model using the globally distributed Rhamnaceae. We collected functional trait data (specific leaf area, leaf area, spinescence, leaf phenology, growth form and leaf margin type) and biome data to test for trait convergence in MTEs, for models of trait evolution and ancestral state reconstruction and for the effect of traits on speciation and extinction rates, using a phylogenetic framework. We show that leaf functional traits evolve to three optima, which correspond to (a) the edaphically specialized Australian and Cape MTEs (AC), (b) the mediterranean-type climates, but edaphically normal Chile, California and Mediterranean Basin (CCM), and (c) the non-mediterranean habitats. We find that Rhamnaceae in CCM are predominantly characterized by non-sclerophylly, the ancestral state in Rhamnaceae, and Rhamnaceae in AC by sclerophylly. These leaf character syndromes have evolved prior to mediterranean climates in MTEs, thereby failing to be adaptive to this selective regime. However, sclerophylly evolved contemporaneously with the transitions to AC, and may therefore be an adaptation to nutrient-poor soils. The evolution of sclerophylly has contributed to increased diversification rates of Pomaderreae in Australia and Phyliceae in the Cape, by reducing extinction rates and thereby facilitating evolutionary persistence. The historical relatively stable conditions in AC are consistent with this persistence hypothesis. Synthesis. In this study we integrate the fields of macroevolution and ecology and show that low extinction rates may not only account for the ecological, but also for the floristic dominance of sclerophylly in the hyperdiverse Australian and Cape mediterranean-type ecosystems.

长期以来，全球范围内的五大地中海型生态系统（Mediterranean-type Ecosystems, MTEs）间的形态趋同现象，被学界解读为对各系统间气候相似性的适应。本研究以全球分布的鼠李科（Rhamnaceae）类群为研究对象，对这一经典模型提出挑战。我们通过系统发育框架（phylogenetic framework），收集了功能性状数据（包括比叶面积（specific leaf area）、叶面积（leaf area）、具刺性（spinescence）、叶片物候（leaf phenology）、生长型（growth form）及叶缘类型（leaf margin type））与生物群区（biome）数据，用以检验地中海型生态系统内的性状趋同现象、性状进化模型与祖先状态重建（ancestral state reconstruction）结果，以及性状对物种形成和灭绝速率的影响。研究结果显示，叶片功能性状的进化存在三个最优值，分别对应：(a) 土壤特化的澳大利亚与好望角地中海型生态系统（Australian and Cape MTEs, AC）；(b) 具备地中海型气候但土壤正常的智利、加利福尼亚与地中海盆地（Chile, California and Mediterranean Basin, CCM）；(c) 非地中海型生境。我们发现，CCM类群中的鼠李科植物以非硬叶性（non-sclerophylly）为主要特征，这也是鼠李科的祖先性状；而AC类群中的鼠李科植物则以硬叶性（sclerophylly）为典型特征。这些叶片性状综合征（leaf character syndromes）在地中海型生态系统出现地中海气候之前就已经进化完成，因此并非对该选择压力环境（selective regime）的适应。但硬叶性状的进化与类群向AC生态系统的转变同步发生，因此可能是对贫瘠土壤环境的适应。硬叶性状的进化通过降低灭绝速率、促进类群的进化存续，提升了澳大利亚潘诺马德雷族（Pomaderreae）与好望角菲莉斯族（Phyliceae）的多样化速率。AC生态系统历史上相对稳定的环境条件，也与这一存续假说相符。研究总结：本研究整合了宏观进化（macroevolution）与生态学领域的研究方法，结果表明，较低的灭绝速率不仅可以解释硬叶性状在澳大利亚与好望角高物种多样性的地中海型生态系统中的生态优势，还能解释其区系主导地位。