Gradual and quantum genome size shifts in the hystricognath rodents

We assessed genome size variation by flow cytometry within and among 31 species of nine families of African and South American hystricognath rodents. Interspecific variation was extensive and genome size was relatively high among the South American radiation whereas only moderate variation and smaller estimates of genome size were observed in the African counterparts. The largest genome size, indicating tetraploidy was recorded in the South American octodontid, Tympanoctomys barrerae (16.8 pg DNA). This quantum shift in DNA content represents a novel mechanism of genome evolution in mammals. As expected in polyploid organisms, varying nucleotypic effects were observed in the dimensions of the sperm cells and lymphocytes of T. barrerae. The role of control mechanisms that influence cell dimensions in polyploid organisms is discussed.