Whole-genome sequencing and phylogenetic analysis of Anolis adenovirus 2 reveals conserved genome organization and gene-specific evolutionary patterns

Adenoviruses, which infect vertebrates, have a rich history of evolution that includes both host switching and coevolution, particularly within Barthadenovirus, a genus that infects squamate reptiles, birds, and mammals. Potential host-switching events can be identified by comparing the evolutionary histories between viruses and their hosts; however, many Barthadenovirus phylogenies have been inferred based on a limited number of easily-amplifiable gene segments. Whole-genome sequencing of novel strains of Barthadenovirus can provide greater phylogenetic confidence, and therefore more accurately identify host-switching when it occurs. Here, we present the coding-complete whole-genome sequence, annotation, reconciled species tree, and molecular evolution analyses of two isolates of Anolis adenovirus 2, a member of Barthadenovirus. Our two isolates of Anolis adenovirus 2 are sister lineages with very high sequence identity. Our results support existing hypotheses regarding the ancestral hosts of Barthadenovirus (squamate reptiles), and proposed host switching events within and between squamate reptiles and other vertebrate classes. We leverage our novel genome annotations to perform comparative synteny analyses, identifying a set of shared genes across Barthadenovirus whose gene order is largely conserved within the genus. Finally, our molecular evolution analyses highlight trends in evolutionary pressures on individual genes: Genes associated with viral replication and structure have experienced slower rates of evolution than those encoding proteins involved in host interaction. Our two sequenced isolates of Anolis adenovirus 2 add to an expanding number of adenovirus genomic resources and facilitate future investigations into the patterns and processes shaping adenovirus diversification.