Evolutionary DNA variation in Papaver

In 23 species of Papaver L., 2C nuclear DNA amounts range from 4.64 pg in Papaver persicum (2n = 14) to 22.43 pg in Papaver orientale (2n = 42), revealing a fivefold variation within the genus. However, such variation is limited to only twofold among the species that have the same chromosome number (2n = 14). The distribution of DNA is discontinuously spread over six groups in the genus. A strong positive correlation exists between nuclear DNA content and metaphase chromosome length. Viewed in the context of evolutionary divergence, it is revealed that DNA reduction has taken place in conjunction with speciation. This is achieved by equal reduction to each chromosome independent of chromosome size, as apparent from the estimated DNA values for individual chromosomes within the complements. The diminution in DNA amount with evolutionary specialisation appears to be a genomic strategy to dispense with the less important DNA associated with heterochromatic segments. The uniform distribution of such dispensible DNA throughout the complement is probably nucleotypically conducive to allow the genomic loss to be adaptationally operative, lest it affects the very survival of the evolving species.Key words: Papaver, evolution, DNA content, DNA systematics.