Response to Comment on "Transitions to Asexuality Result in Excess Amino Acid Substitutions"

Abstract

Asexual populations experience a reduction in the efficiency of selection when compared with sexual populations. Because asexual lineages of Daphnia pulex exhibit no consistent change in mitochondrial base-composition bias, Butlin suggests that this bias is not maintained by selection. On the basis of frequencies of polymorphic directional base changes, we suggest that it predominantly reflects mutation bias.