The genome of the green anole lizard and a comparative analysis with birds and mammals

Abstract

The first non-avian reptile genome has been sequenced, that of the North American green anole lizard (Anolis carolinensis). The anole is an emerging model for the study of adaptive radiation and convergent evolution. The genome includes a previously unknown X chromosome, with no homology to known amniote sex chromosomes, and microchromosomes that share a common ancestry with those in birds, but without their unusual characteristics. The evolution of the amniotic egg was one of the great evolutionary innovations in the history of life, freeing vertebrates from an obligatory connection to water and thus permitting the conquest of terrestrial environments1. Among amniotes, genome sequences are available for mammals and birds2,3,4, but not for non-avian reptiles. Here we report the genome sequence of the North American green anole lizard, Anolis carolinensis. We find that A. carolinensis microchromosomes are highly syntenic with chicken microchromosomes, yet do not exhibit the high GC and low repeat content that are characteristic of avian microchromosomes2. Also, A. carolinensis mobile elements are very young and diverse—more so than in any other sequenced amniote genome. The GC content of this lizard genome is also unusual in its homogeneity, unlike the regionally variable GC content found in mammals and birds5. We describe and assign sequence to the previously unknown A. carolinensis X chromosome. Comparative gene analysis shows that amniote egg proteins have evolved significantly more rapidly than other proteins. An anole phylogeny resolves basal branches to illuminate the history of their repeated adaptive radiations.