Description
- Abstract:
- Most important organismal adaptations are not actually single traits, but complex trait syndromes that are evolutionarily integrated into a single emergent phenotype. In plants, crassulacean acid metabolism (CAM) is a complex trait that improves water use and photosynthetic efficiency under drought and temperature stress. Though CAM is an important and ubiquitous ecological adaptation, having evolved hundreds of times from the more common C3 photosynthetic pathway, we still know very little about its evolutionary assembly. In addition to fully expressed constitutive CAM, there are other well-known phenotypes that perform small amounts of CAM in an otherwise C3 background (i.e. C3-CAM intermediates). Untangling the evolution of CAM requires piecing together the genetic, biochemical, anatomical, physiological, and ecological aspects of this trait and reconstructing the evolutionary order of its assembly. In this study we characterize most of these properties associated with CAM evolution across Australian Calandrinia and species representatives from the Montiaceae and wider sub-order, Portulacineae. We use a targeted gene capture approach to sequence hundreds of loci across Australian Calandrinia (~70 species) and Montiaceae, resulting in the first and complete phylogeny for the lineage. We estimate the divergence of Australian Calandrinia from its sister lineage to ~ 30 Ma, concurrent with separation of Australia from Antarctica, and show that although the lineage radiated across inland Australia during the mid-Miocene, coincident with the initial onset of aridity, diversification slowed dramatically with the establishment of severe aridity. Through robust phylogenetic and phenotypic analyses we demonstrate that C3-CAM phenotypes are anatomically intermediates between C3 and full CAM, and that the evolution of CAM biochemistry precedes the evolution of full CAM morphological and anatomical traits. Given the number of C3-CAM reversals detected within Australia Calandrinia and the Montiaceae, we propose a model of CAM evolution that allows for lability and reversibility among C3-CAM phenotypes and C3 photosynthesis, and where C3-CAM evolves prior to the realization of full CAM. Finally, we hypothesize that once a species evolves full CAM, with the associated anatomical changes such as extreme succulence, large cells, and little intercellular airspace, reversibility back to C3 or C3-CAM photosynthesis may no longer be evolutionarily accessible.
- Notes:
- Thesis (Ph. D.)--Brown University, 2018
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Citation
Hancock, Lillian Pine,
"Untangling the evolution of CAM photosynthesis within Australian Calandrinia (Montiaceae)"
(2018).
Ecological and Evolutionary Biology Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/58sc-qr20
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Ecological and Evolutionary Biology Theses and Dissertations
Theses and Dissertations for the Ecological and Evolutionary Biology department....