synergistic epistasis
Schultz ST & Lynch M 1997 Mutation and extinction: the role of variable mutational effects, synergistic epistasis, beneficial mutations, and degree of outcrossing. Evolution 51:1363-1371.
- the extent to which synergistic epistasis between mutational effects can reduce the vulnerability of a population to the accumulation of deleterious mutations
- the evidence for such epistasis is weak
- relying almost entirely on a single data point generated by Mukai (1969)
- interest in it is again well motivated on theoretical grounds
- whether epistasis will increase or decrease the vulnerability of a population to mutation accumulation again depends on the effective population size and on the form of the distribution of mutational effects
- even extremely strong epistasis appears to increase the expected lifetime of a population by less than a factor of 10
- in small partially selfing populations, synergistic epistasis actually increases the vulnerability to extinction
- with a continuous distribution of mutational effects, there are always likely to be some deleterious mutations with small enough effects to allow fixation
- once fixed, these mutations exert effects that can then become permanently magnified by synergistic epistasis as subsequent mutations accumulate
- unless the synergistic interactions among all deleterious mutations are strong enough to prevent fixation, it does not appear that epistasis can prevent an ultimate decline in fitness in a small population
- (Butcher 1995)
