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Abstract Detail


Lujan, Manuel [1], McDade, Lucinda [2].

Evolution of CAM photosynthesis in Neotropical Clusia (Clusiaceae): insights from leaf anatomy, biochemistry and climate.

Crassulacean acid metabolism (CAM) is considered an adaptation to reduce water loss in plants inhabiting water-limited environments. CAM has evolved multiple times independently in a number of lineages, particularly in plants occurring in dry habitats or of epiphytic habit. The Neotropical genus Clusia includes about 300 species of trees, shrubs and hemiepiphytes with remarkable morphological diversity and physiological plasticity. The genus is considered the only group known to include trees with CAM; it has been subject of numerous physiological studies, although little is known about the evolution of CAM. With the aim of describing the evolutionary history of CAM photosynthesis in Clusia, we reconstruct a phylogenetic tree using data from restriction site associated DNA sequencing and undertake phylogenetic comparative analyses to evaluate seven leaf anatomical traits, carbon isotope ratios and bioclimatic variables calculated for 109 samples of 56 species of Clusia and two related genera. Species distributed throughout the elevation range of the genus (i.e., near the sea level to > 3.000 m elevation), as well as across the latitudinal range of the group (i.e., central Mexico to southern Bolivia), were included in this study. Phylogenetic least squares regression analyses indicate that leaf thickness, palisade mesophyll thickness and cell size are positively correlated with carbon isotope ratios. Likewise, these traits are strongly correlated with bioclimatic variables related to the severity of the dry season, estimated as precipitation during the driest periods. Intercellular air space and length of mesophyll exposed to air displayed their maximum values in both extant species and reconstructed nodes among species of Clusia sect. Anandrogyne, a lineage not known to have CAM. This suggests that well-aerated mesophyll may impeded the evolution of CAM. Ancestral state reconstructions indicate that the most recent common ancestor of Clusia and of all the main lineages in the genus possessed leaf anatomical traits correlated with C3 photosynthesis, and that the evolution of CAM-related leaf anatomy evolved before the appearance of CAM. Analysis of evolutionary shifts of leaf anatomical traits indicates convergent evolution of CAM-related traits across a number of independent lineages within the genus. Our results show that leaf anatomical features associated with in CAM activity can be quantified and analyzed separately to investigate their role in CAM evolution.

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1 - Rancho Santa Ana Botanic Garden, 1500 N College Ave, Claremont, CA, 91711, United States
2 - 1500 N. College Avenue, Rancho Santa Ana Botanic Garden, Claremont, CA, 91711, United States

Leaf anatomy

Presentation Type: Oral Paper
Session: 26, ASPT Cooley Awards II
Location: 110/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 2:30 PM
Number: 26005
Abstract ID:962
Candidate for Awards:George R. Cooley Award

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