18 optimality models can differentiate among fitness

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18 Optimality models can differentiate among fitness criteria Gross energetic gain (G) Total energetic expenditure or loss (L) Total time (T) per foraging cycle optimization criterion: - net energy gain per unit time = (G - L) T - net energy gain per unit energy expended = (G - L) L A worker's condition deteriorates as a function of the amount of flight performed Prediction (6) Schmid-Hempel, Kacelnik & Houston Behav. Ecol. Sociobiol. (1985)
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19 What can we gain from an optimality model? Testing understanding of constraints and tradeoffs Testing understanding of fitness function Suggestions for new experiments and quantitative questions
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20 Interpreting an optimality model “The final step in the optimality approach is to test the predictions against the observations. If they fit, then the model may really reflect the forces that have molded the adaptation. If they do not, we may have misidentified the strategy set , or the optimization criterion , or the payoffs ; or the phenomenon we have chosen may not any longer be adaptive …“ Parker & Maynard-Smith, Nature (1990)
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21 “…by reworking our assumptions, we modify our model and revise and retest the predictions. This has been criticized as being an iterative procedure leading inevitably to a fit. But this is how science works; theories can only be discarded when they are disproven or found to be unrealistic.” Parker & Maynard-Smith, Nature (1990) Interpreting an optimality model
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22 Why are optimality models at the molecular level maturing now? After answering the who and how questions Requires quantitative tools and information recently becoming available in biology We begin to design and build biological systems
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23 The number you need, with reference in one minute BioNumbers – Useful biological numbers database Wiki-like, users edit and comment Over 3500 properties & 5000 users/month
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24 Warm-up: trying to beat nature at design How to transform 5 carbon sugars into 6 carbon sugars? (e.g from cell wall or nucleic acids glycolysis) 6 x x 5
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The pentose phosphate pathway defined as a game Goal: Turn 6 Pentoses into 5 Hexoses Rules: Transfer 2-3 carbons between two molecules Never leave a molecule with 1-2 carbons Optimization function: ° Minimize the number of steps (simplicity) 5 5 5 5 5 5 6 6 6 6 6 ? E. Meléndez-Hevia et al. (Journal of theoretical Biology 1994) Among equally long solutions prefer the one using the least number of carbons in molecules
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26 Serious, take 5 minutes and six 5 carbons and try it out
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Solution to Pentose Phosphate game in 7 steps
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Solution to Pentose Phosphate game in 7 steps Corresponds to natural pathway Doesn't explain why the rules exist Supports the idea of simplicity
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29 Are there simplifying principles to the structure of the central carbohydrate metabolism network?
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