Dynamics of genome size evolution in birds and mammals

Deciphering the forces and mechanisms modulating genome size is central to our understanding of molecular evolution, but the subject has been understudied in mammals and birds. We took advantage of the recent availability of genome sequences for a wide range of species to investigate the mechanism underlying genome size equilibrium over the past 100 million years. Our data provide evidence for an "accordion" model of genome size evolution in birds and mammals, whereby the amount of DNA gained by transposable element expansion, which greatly varies across lineages, was counteracted by DNA loss through large segmental deletions. Paradoxically, birds and bats have more compact genomes relative to their flightless relatives but exhibit more dynamic gain and loss of DNA.