GENOME SIZE VARIATION IN APHIDS

Genome sizes of invertebrates vary at least 1000-fold, with small genomes most common in species with rapid development. Although few groups have been studied, there is growing evidence that closely related taxa often show quantum shifts in genome size without a co-ordinate shift in chromosome numbers. The present study provides the first detailed information on genome sizes in aphids, a group of insects recognized for their rapid developmental rates. The results of scanning microdensitometry of 34 aphid species show that diploid genome sizes show a 5-fold range (0.36-1.77 pg) which is unassociated with chromosome number. Genome sizes appear to vary in a discontinuous fashion, with quanta corresponding to the basal genome size detected in this study. As genome size is positively associated with body size, quantum shifts in genome size may have led to rapid change in this important life-history character. The small genomes found in some aphid species are among the lowest yet reported for insects, reinforcing the linkage between developmental rate and genome size.