CONSERVATIVE GENOME SIZE AND RAPID CHROMOSOMAL EVOLUTION IN THE SOUTH-AMERICAN TUCO-TUCOS (RODENTIA, CTENOMYIDAE)

Genome size (the amount of DNA per cell) was measured by flow-cytometr ic analysis in seven species of a chromosomally variable rodent genus: Ctenomys boliviensis, C conoveri, C. frater, C leucodon, C. lewisi, C . opimus, and C. steinbachi. The mean genome size of these species was 7.19 pg DNA and little inter- and intra-specific variation was observ ed. Genome size was not correlated with diploid number, suggesting tha t chromosomal evolution at this level is independent of total DNA cont ent. A hypothetical taxonomic unit optimization procedure was carried out using genome size change on a Wagner tree derived from allozyme da ta. Allozyme evolution and genome size change are linked by a weak, bu t significant, negative correlation suggestive of preferential genic e volution in the absence of genome size evolution.