the major transitions in evolution: a physiological perspective
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The Major Transitions in Evolution: A Physiological Perspective. Andrew H. Knoll Harvard University. 1. Replicating molecules Populations of molecules in compartments 2. Independent replicators chromosomes 3. RNA DNA and proteins 4. Prokaryotes Eukaryotes - PowerPoint PPT PresentationTRANSCRIPT
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The Major Transitions in Evolution: A Physiological
Perspective
Andrew H. Knoll
Harvard University
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1. Replicating molecules Populations of molecules in
compartments2. Independent replicators chromosomes3. RNA DNA and proteins4. Prokaryotes Eukaryotes5. Asexual clones Sexual
reproduction6. Single cells Multicellular
organisms7. Solitary individuals
Colonies with non-reproductive castes
8. Primate societies Human societies (language)
To
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Physiological/Metabolic Major Transitions
Autotrophy1. From reliance on abiotic synthesis to chemosynthesis2. From chemosynthesis to photosynthesis3. From anoxygenic to oxygenic photosynthesis4. From reliance on environmental N to nitrogen fixation
Heterotrophy5. From fermentation to respiration6. From anaerobic respiration to aerobic respiration7. From absorption of organic molecules to phagocytosis8. From diffusion to bulk transport 9. Technology
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Photosynthesis
Van Niel Equation: CO2 + 2H2A CH2O + H2O + 2A
Electron donor can be water, but also Fe2+, As3+, H2S, H2, organic molecules
http://en.wikipedia.org/wiki/File:Z-scheme.png
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Primary production, limited by electron supply before oxygenic
photosynthesis?
Canfield et al. (2006)
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Nealson (1997)
What about earlyheterotrophy?
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Nealson (1997)
1. Importance of Fe in Archean carbon cycle
2. Limitations on chemoautotrophy imposed by oxidant pool
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Conceptual model of Archean and iron formation deposition,
derived from the biological oceanic iron cycle.
Fischer and Knoll (2009)
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Several lines of evidence indicate
oxygenation 2.4 Ga
• Banded iron formation • Detrital uraninite, siderite,
and pyrite• Paleosols• Sulfur isotopes
Our hero
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Falcon et al. (2010)
1332/1232
2211/2057
3028/2519
Plastids
Heterocysts
N-fixers
What drove oxygenation?
Assumption of cyanobacterial origins: 3500/2700 Ma
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How much O2 accumulated?Lyons and Reinhard (2009)
Maliva et al. (2005)
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Nealson (1997)
Accumulating oxygen alters carbon cycle and its constituent metabolisms
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After Anbar and Knoll (2002)
Scott et al. 2008Shen et al. (2003)
Brocks et al. (2005)
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De Duve (2007)
The Eukaryotic Cell
1. Qualifies as a major transition in the scheme of MS & S.2. What are its metabolic or physiological consequences?3. Briefly consider phagocytosis and the acquisition of energy metabolisms.
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Phagocytosis
1. Enables particle capture, including bacterial and protistan cells (and small animals)
2. Introduces predation as a key ecological process
3. Changes physical nature of organic C acquisition, but not metabolic means of generating energy
Image shows amoeba eating a yeast cell; Pierre Casson (http://www.forschung3r.ch)
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In eukaryotes, energy metabolism is largely the product of endosymbiosis, incorporating bacterial cells. -- Aerobic respiration mitochondria proteobacteria-- Oxygenic photosynthesis chloroplast cyanobacteria
Innovation vs. limitation.
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Consequences of redox structure for eukaryotic organisms?
• Mitochondria must have arisen in a global setting where marine oxygen levels were extremely low and sulfide levels were high. Furthermore, the first ~1 billion years (at least) of eukaryote diversification occurred in a marine environment marked by low oxygen, widespread anoxia and high sulfide.
• Hypoxia/anoxia• Sulfide toxicity (interfere with cytochrome c oxidase in mitochondria)• Fixed nitrogen availability
Martin et al. (2003)
Johnston et al. (2009)
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Photosynthetic eukaryotes in mid-Proterozoic oceans
• 0.5 million or more species today• In mid-Proterozoic oceans,
problematic• Capacity to fix carbon was not
accompanied by the ability to fix nitrogen
• In mid-Proterozoic oceans, limited fixed nitrogen in photic zone.
• Ecological advantage to photoautotrophs able to fix N2.
Butterfield (2000)
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Mitochondriate eukaryotes in mid-Proterozoic oceans
• Systemic inhibition by sulfide – interferes with cytochrome c oxidase function in mitochondria
• Widespread sulfide in mid-Proterozoic oceans may have challenged eukaryotes in many marine environments.
• Mitochondrial adaptation to anoxic metabolism occurs (hydrogenosome, mitosome), but is a one way street
• When did environmental challenges of sulfide and fixed nitrogen fade?
Porter and Knoll (2000)
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Subsurface sulfide decline
• Johnston et al. (2010) – Ferruginous subsurface waters begin at least 800 Ma, concomitant with widespread rifting of supercontinent Rodinia
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Courtesy of N. Butterfield
Courtesy of Phoebe Cohen
Porter et al. (2003)
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More scales…P. Cohen, PhD thesis
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Multicellularity
• A major transition in MS & S scheme
• But a common transition – fully 1/3 of the 119 major eukaryotic clades recognized by Adl et al. (2005) have evolved simple multicellularity; most have limited diversity
• Six (possibly 7) clades have evolved complex multi-cellularity; 95% of all described eukaryotic species
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1. In complex multicellular organisms, only a subset of cells are in direct contact with the environment.
2. In organisms with 3-D multicelluarity, diffusion will strongly affect both metabolism and development.
The Problem of Diffusion
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Diffusion and metabolism
• Diffusion limits size attainable at any given pO2
• Circumventing diffusion:– Mechanisms to
enhance directional cell-cell transfer (plasmodesmata, gap junctions, incomplete septation)
– Specialized cell and tissue types for bulk transfer (phloem, trumpet hyphae, circulatory systems)
Knoll and Hewitt (2011); left after Runnegar (1991)
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Diffusion and development
• Only surface cells directly encounter environment
• Gradient in concentration of signaling molecules develops
• Gradient develops in diffusible environmental factors that induce cell differentiation in unicellular eukaryotes modification (e.g., nutrients, oxygen)
Schlichting (2003)
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Size
Nutrient/Signal Gradient
Differentiation
Development feeds back on physiology
With time, cross a functional threshold that promotes the diversity (evolvability?) of complex multicellular clades.
MAKES ECOLOGICAL FEEDBACKS POSSIBLE.
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Size
Nutrient/Signal Gradient
Differentiation
Development feeds back on physiology
With time, cross a functional threshold that promotes the diversity (evolvability?) of complex multicellular clades.
MAKES ECOLOGICAL FEEDBACKS POSSIBLE.
PO2
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When did atmosphere/ocean begin its transition to a more modern state?
Derry et al. (1992)
Canfield and Teske (1995)
Scott et al. (2008) Dahl et al. (2010)
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24-isopropylcholestane; Love et al. (2009)
(??)
Ediacaran-Cambrian Animal Radiation
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The Evolutionary
Present
Peter Brewer (MBARI)
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• Major transitions in physiology both track and drive environmental changes in Earth history
• Might characterize evolutionary trajectories wherever life emerges
The Punch Line
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Thanks to …
• Members of the Knoll lab (especially Tais Dahl, Ben Gill and Phoebe Cohen)
• Colleagues further afield, especially Dave Johnston and Don Canfield
• Funding from NSF, NASA Exobiology, and the Agouron Institute