phenofirst

Prev: Multi-level modelling Next: Opportunity vs optimality


 * TODO LIST**
 * CLARIFICATION: Better integration into story: why interesting
 * CLARIFICATION: higher order catalysis, then focus on **nice** nets (?)
 * REF Baldwin
 * REF Waddington

=Phenotype-first evolution=

Here we take a look at Kaneko & Yomo's (1997) work on **isologous differentiation**.

Model

 * organisms are metabolic networks
 * they take up nutrient A, make B, using catalyst C
 * nutrients diffuse through membrane
 * cell division when volume doubles

Results
Given that all organisms have the same network and environment how can they differentiate?
 * random networks: higher order catalysis, then focus on **nice** nets (?)
 * certain % of networks have **chaotic** dynamics (which is interesting!)
 * cells divide: not in space but into the identical environment (just a little noise to get out of phase)
 * but they do **differentiate**
 * little bit of noise in the environment
 * effect depends on where in chaotic attractor: noise can push networks apart
 * cell differentiation: some attractors allow for further types
 * you can get cell type lineage differences, i.e. to get kidney cell one needs a kidney precursor!
 * if cells are taken away: system goes back to same ratios of different cell types which is quite robust (i.e. compete for nutrient and use different concentrations? or just certain probabilities to get into certain attractors?)
 * dynamical systems are able to differentiate with nicely robust (adaptive) properties: will evolutionary system lead to such processes?

Here we look at Kaneko and Yomo's (2000) study on sympatric speciation


 * starting in a certain attractor and starting with phenotypic plasticity
 * evolve from phenotypic plasticity: developmental canalization
 * by bringing in different phenotypic states: subject you to different selection pressures
 * partly heritable: evolutionary process will go on and can lead to genetic differences where each in only one cell type
 * epigenetic inheritance: e.g. methylation, instead cell attractor in which it remains after cell division (cf making a flagellum over several generations!).

In the critters we saw that fitness criteria don't change. In Kaneko's work there is partial inheritance, finally inheritance takes over through genetic assimilation. It is less fixed.
 * can or cannot inherit
 * and can change it

(see also Waddington: drosophila wings) (Baldwin effect?)

Next: Opportunity vs optimality