Genetic changes within an aphid clone: Homogenization of rDNA intergenic spacers after insecticide selection

Abstract

A single asexual maternal lineage (i.e. clone) of the greenbug aphid, Schizaphis graminum (Rondani) was repeatedly selected with the insecticide disulfoton (O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodioate). A parallel colony of the non-selected clone was also maintained. After approximately 200 generations (4 years) of continuous selection, both the selected and non-selected clones were assayed for changes in intergenic spacer (IGS) length variants of the rRNA cistron. No changes in sets of IGS variants were detected in the non-selected clone. However, the selected clone was found to have lost three variants present in the non-selected clone. This probably occurred by unequal cross-over between sister chromatids, whereby the cistron became homogenized by an increase of frequency of two smaller variants. This documents a large-scale genetic change occurring within the rRNA cistron in a parthenogenetically reproducing aphid. © 2003 The Linnean Society of London.