near neutrality & compensatory evolution
Ohta T 1992 The nearly neutral theory of molecular evolution. Annu Rev Ecol Syst 23:263-286.
- in view of the importance of negative selection caused by constraints, it is likely that many nearly neutral mutants are very slightly deleterious
- I propose that a substantial fraction of mutant substitutions at the molecular level are caused by random fixation of very slightly deleterious mutations
- it is likely that a slightly deleterious base substitution is followed by a slightly advantageous (compensatory) substitution
- this model is different from the landscape model of Gillespie (27)
- we are concerned with the interaction effect of random drift and natural selection
- Gillespie treated the situation of strong selection and weak mutation
- in the fixed model, the effect of each substitution remains and affects subsequent substitutions by changing the mean fitness
- in terms of the higher order structure of a protein, substitutions that occur at many amino acid sites do not behave independently
- the fixed model I believe is a better description of nature
- the nearly neutral model now incorporates very slightly advantageous mutations
- the concept of near neutrality approaches that of selectionists
