University of Groningen
The evolution of the bacterial chemotaxis network
Nakauma Gonzalez, Jose Alberto
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2019
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Nakauma Gonzalez, J. A. (2019). The evolution of the bacterial chemotaxis network. University of
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Stellingen behorende bij het proefschrift
Evolution of the bacterial chemotaxis network
Alberto Nakauma
1. In rugged fitness landscapes, evolution can reach an adaptive peak within a
few mutational steps, but it also quickly gets stuck at a local optimum unless
selection is fluctuating.
Chapter 2, this thesis; Marjon de Vos et al. (2015)
2. Important phenotypic characteristics of chemotactic behaviour are not
universally optimal, but fine-tuned to the ecological context.
Chapter 2, this thesis
3. The observation that simulated wildtype Escherichia coli perform better in
dynamic than in static resource gradients suggests that E. coli’s chemotactic
network has been optimized to function in dynamic environments.
Chapter 2 and 3, this thesis
4. The genotype-phenotype map spans several levels of organization. Therefore,
even if mutations have a straightforward molecular effect, their ultimate effect
on fitness tends to be non-linear and contingent on genetic background.
Chapter 3, this thesis
5. Since the house-of-cards mutation model is an adequate null-model for the
fitness of non-chemotactic genotypes, exaptation rather than ‘tinkering from
scratch’ is a likely scenario for the evolution of the chemotactic network.
Chapter 4, this thesis
6. Chemotactically deficient ∆CheZ mutants can restore chemotaxis by fixing
adaptive compensatory mutations, but the incorporation of CheZ in the genome
of E. coli increases the number of accessible high-fitness genotypes, as well as
their average chemotactic performance.
Chapter 4, this thesis
7. In very large populations, selection may favor genotypes with skewed
offspring distributions, even though such genotypes perform poorly most of the
time.
Chapter 5, this thesis
8. Nothing in systems biology makes sense except in the light of evolution.
Gutiérrez and Maere, 2014
9. There is one thing the history of evolution has taught us. That life will not be
contained. Life breaks free. Life expands to new territories. Life… finds a way.
Chaos theorist Dr. Ian Malcolm, Jurassic Park.
