PDF(Pubmed)
Abstract：
Epiphytism has evolved repeatedly in plants and has resulted in a considerable number of species with original characteristics. Because water supply is generally erratic compared to that in soils, succulent forms in particular are widespread in epiphytic species. However, succulent organs also exist in terrestrial plants, and the question of the concomitant evolution of epiphytism and succulence has received little attention, not even in the epidendroid orchids, which account for 67.6 % of vascular epiphytes.
We built a new time-calibrated phylogenetic tree of Epidendroideae with 203 genera treated in genus Orchidacearum, from which we reconstructed the evolution of epiphytism as well as traits related to water scarcity (stem and leaf succulence and the number of velamen layers), while testing for the correlated evolution between the two. Furthermore, we estimated the ancestral geographical ranges to evaluate the palaeoclimatic context in which epiphytism evolved.
Epiphytism evolved at least three times: 39.0 million years ago (Mya) in the common ancestor of the Malaxideae and Cymbidieae that probably ranged from the Neotropics to Southeast Asia and Australia, 11.5 Mya in the Arethuseae in Southeast Asia and Australia, and 7.1 Mya in the neotropical Sobralieae, and it was notably lost in the Malaxidiinae, Collabieae, Calypsoeae, Bletiinae and Eulophiinae. Stem succulence is inferred to have evolved once, in a terrestrial ancestor at least 4.1 Mya before the emergence of epiphytic lineages. If lost, stem succulence was almost systematically replaced by leaf succulence in epiphytic lineages.
Epiphytism may have evolved in seasonally dry forests during the Eocene climatic cooling, among stem-succulent terrestrial orchids. Our results suggest that the emergence of stem succulence in early epidendroids was a key innovation in the evolution of epiphytism, facilitating the colonization of epiphytic environments that later led to the greatest diversification of epiphytic orchids.
We built a new time-calibrated phylogenetic tree of Epidendroideae with 203 genera treated in genus Orchidacearum, from which we reconstructed the evolution of epiphytism as well as traits related to water scarcity (stem and leaf succulence and the number of velamen layers), while testing for the correlated evolution between the two. Furthermore, we estimated the ancestral geographical ranges to evaluate the palaeoclimatic context in which epiphytism evolved.
Epiphytism evolved at least three times: 39.0 million years ago (Mya) in the common ancestor of the Malaxideae and Cymbidieae that probably ranged from the Neotropics to Southeast Asia and Australia, 11.5 Mya in the Arethuseae in Southeast Asia and Australia, and 7.1 Mya in the neotropical Sobralieae, and it was notably lost in the Malaxidiinae, Collabieae, Calypsoeae, Bletiinae and Eulophiinae. Stem succulence is inferred to have evolved once, in a terrestrial ancestor at least 4.1 Mya before the emergence of epiphytic lineages. If lost, stem succulence was almost systematically replaced by leaf succulence in epiphytic lineages.
Epiphytism may have evolved in seasonally dry forests during the Eocene climatic cooling, among stem-succulent terrestrial orchids. Our results suggest that the emergence of stem succulence in early epidendroids was a key innovation in the evolution of epiphytism, facilitating the colonization of epiphytic environments that later led to the greatest diversification of epiphytic orchids.
摘要：
目的：附生在植物中反复进化，并导致了相当数量的具有原始特征的物种。因为与土壤相比，供水通常不稳定，肉质形式尤其广泛存在于附生物种中。然而,肉质器官也存在于陆生植物中，附生和肉质的伴随进化问题很少受到关注，甚至在epidendroid兰花中也没有，占血管附生植物的75%。
方法：我们构建了一个新的时间校准的Epidendoideae系统发育树，其中203属处理在Orchidacearum中，从中我们重建了附生的进化以及与缺水有关的特征（茎和叶的肉质和绒毛层的数量），同时测试两者之间的相关进化。此外，我们估计了祖先的地理范围，以评估附生症演变的古气候环境。
结果：附生症至少进化了三次：39.0Myr之前，在Malaxideae和Cymbidieae的共同祖先中，可能从新热带到东南亚和澳大利亚，11.5Myrago在东南亚和澳大利亚的Arethuseae，7.1Myrago在新热带Sobralieae中，尤其是在Malaxidiinae中丢失，同事,Calypsoeae，Bletiinae,和Eulophiinae。据推测，茎肉质已经进化了一次，在附生谱系出现之前至少在4.1Myr前的陆地祖先中。如果丢失了,附生谱系中的茎肉质几乎被叶片肉质替代。
结论：在始新世气候降温期间，在季节性干燥的森林中可能发生了附生体，在茎多汁的陆生兰花中。我们的研究结果表明，在早期的附生体中出现茎肉质是附生体进化的关键创新，促进附生环境的定殖，后来导致附生兰花的最大多样化。
方法：我们构建了一个新的时间校准的Epidendoideae系统发育树，其中203属处理在Orchidacearum中，从中我们重建了附生的进化以及与缺水有关的特征（茎和叶的肉质和绒毛层的数量），同时测试两者之间的相关进化。此外，我们估计了祖先的地理范围，以评估附生症演变的古气候环境。
结果：附生症至少进化了三次：39.0Myr之前，在Malaxideae和Cymbidieae的共同祖先中，可能从新热带到东南亚和澳大利亚，11.5Myrago在东南亚和澳大利亚的Arethuseae，7.1Myrago在新热带Sobralieae中，尤其是在Malaxidiinae中丢失，同事,Calypsoeae，Bletiinae,和Eulophiinae。据推测，茎肉质已经进化了一次，在附生谱系出现之前至少在4.1Myr前的陆地祖先中。如果丢失了,附生谱系中的茎肉质几乎被叶片肉质替代。
结论：在始新世气候降温期间，在季节性干燥的森林中可能发生了附生体，在茎多汁的陆生兰花中。我们的研究结果表明，在早期的附生体中出现茎肉质是附生体进化的关键创新，促进附生环境的定殖，后来导致附生兰花的最大多样化。
