Rate of sequence divergence under constant selection
|Title||Rate of sequence divergence under constant selection|
|Publication Type||Journal Article|
|Year of Publication||2010|
|Authors||Kondrashov AS, Povolotskaya IS, Ivankov DN, Kondrashov FA|
Background: Divergence of two independently evolving sequences that originated from a common ancestor can be described by two parameters, the asymptotic level of divergence E and the rate r at which this level of divergence is approached. Constant negative selection impedes allele replacements and, therefore, it is routinely assumed that it must decelerate sequence divergence. However, its impact on E and on r has not been formally investigated. Results: Strong selection that favors only one allele can make E arbitrarily small and r arbitrarily large. In contrast, in the case of 4 possible alleles and equal mutation rates, the lowest value of r, attained when two alleles confer equal fitnesses and the other two are strongly deleterious, is only two times lower than its value under selective neutrality. Conclusions: Constant selection can strongly constrain the level of sequence divergence, but cannot reduce substantially the rate at which this level is approached. In particular, under any constant selection the divergence of sequences that accumulated one substitution per neutral site since their origin from the common ancestor must already constitute at least one half of the asymptotic divergence at sites under such selection.