The vanishing clone: karyotypic evidence for extensive intraclonal genetic variation in the peach potato aphid, Myzus persicae (Hemiptera:Aphididae)

Analysis of holocentric mitotic metaphase chromosomes of the peach-potato aphid Myzus persicae (Sulzer) clone 33H revealed different chromosome numbers, ranging from 12 to 17 within each embryo, in contrast to the standard karyotype of this species (2n=12). Chromosome length measurements revealed that the observed chromosomal mosaicism is due to recurrent fragmentations of chromosomes X, 1 and 3 due to fragile sites or to hot spots of recombination. Fluorescent in situ hybridization experiments showed that X chromosomes were frequently involved in recurrent fragmentations, in particular their telomeric end opposite to the nucleolar organizer region (NORs). Experiments to induce males showed that M. persicae clone 33H is obligately parthenogenetic. The reproduction by apomictic parthenogenesis, together with a high telomerase expression that stabilized the chromosomes involved in the fragmentations observed in the M. persicae clone 33H, appears to favour the stabilization of the observed chromosome instability.