Genealogical evidence for epidemics of selfish genes.

Some genetic elements spread infectiously in populations by increasing their rate of genetic transmission at the expense of other genes in the genome. These so-called selfish genetic elements comprise a substantial portion of eukaryotic genomes and have long been viewed as a potent evolutionary force. Despite this view, little is known about the evolutionary history of selfish genetic elements in natural populations, or their genetic effects on other portions of the genome. Here we use nuclear and chloroplast gene genealogies in two species of Silene to show the historical pattern of selection on a well known selfish genetic element, cytoplasmic male sterility. We provide evidence that evolution of cytoplasmic male sterility has been characterized by frequent turnovers of mutations in natural populations, thus supporting an epidemic model for the evolution of selfish genes, where new mutations repeatedly arise and rapidly sweep through populations.