title: A macro-ecological perspective on crassulacean acid metabolism (CAM) photosynthesis evolution in Afro-Madagascan drylands: Eulophiinae orchids as a case study.
abstract: Crassulacean acid metabolism (CAM) photosynthesis is an adaptation to water and atmospheric CO2 deficits that has been linked to diversification in dry-adapted plants. We investigated whether CAM evolution can be associated with the availability of new or alternative niches, using Eulophiinae orchids as a case study. Carbon isotope ratios, geographical and climate data, fossil records and DNA sequences were used to: assess the prevalence of CAM in Eulophiinae orchids; characterize the ecological niche of extant taxa; infer divergence times; and estimate whether CAM is associated with niche shifts. CAM evolved in four terrestrial lineages during the late Miocene/Pliocene, which have uneven diversification patterns. These lineages originated in humid habitats and colonized dry/seasonally dry environments in Africa and Madagascar. Additional key features (variegation, heterophylly) evolved in the most species-rich CAM lineages. Dry habitats were also colonized by a lineage that includes putative mycoheterotrophic taxa. These findings indicate that the switch to CAM is associated with environmental change. With its suite of adaptive traits, this group of orchids represents a unique opportunity to study the adaptations to dry environments, especially in the face of projected global aridification.
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, UK.
authors.forename: Ruth E
authors.identifier: http://orcid.org/0000-0002-1304-6185
authors.initials: RE
authors.lastname: Bone
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
authors.forename: J Andrew C
authors.initials: JA
authors.lastname: Smith
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, CH-1015, Switzerland.
authors.forename: Nils
authors.initials: N
authors.lastname: Arrigo
authors.affiliation: Department of Life Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK.
authors.forename: Sven
authors.initials: S
authors.lastname: Buerki
mesh_terms: D044822:Biodiversity; D005075:Biological Evolution; D002247:Carbon Isotopes; D002264:Carboxylic Acids / Q000378:metabolism*; D017753:Ecosystem; D008270:Madagascar; D029595:Orchidaceae / Q000502:physiology*; D010788:Photosynthesis; D010802:Phylogeny; D025341:Principal Component Analysis; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D002264:Carboxylic Acids
keywords: Africa; Eulophiinae; Madagascar; Orchidaceae; climate change; crassulacean acid metabolism (CAM) photosynthesis; shift of niche