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298 | Corredor and Nagy

Figure 10.7 Phylogenetic tree (republished with permission of the Microbiology Society from Marek, A., Kajan, G.L., Kosiol, C., Benko, M.,
Schachner, A., Hess, M. Genetic diversity of species Fowl aviadenovirus D and Fowl aviadenovirus E. J. Gen. Virol. 2016; 97:2323–2332).

among FAdV-D strains and 92.7 and 97.1% among FAdV-E plus ORF24 seem to contribute to the increased size of the left
strains (Marek et al., 2016). end region in members of the FAdV-C species (Corredor et al.,
Adenoviruses are thought to have co-evolved with their hosts. 2006; Marek et al., 2014b). The genome size seems to be also
Their divergence in the nucleotide sequence of the viral genome, determined by the presence of tandem repetitions at the right
multiple host switches and recombinational events between end of the genomes. For example, FAdV-2 and FAdV-9, both
serotypes seems to have driven the evolution of adenoviruses within species FAdV-D, markedly differ in the number of rep-
(Harrach et al., 2011; Wold and Ison, 2013). The presence of etition units and consequently the size of the right end region
viral genes with predicted or established functions of other viral (Corredor et al., 2008).
genes (e.g. parvovirus NS-1) or cellular genes of vertebrate hosts Studies on gene function between mastadenoviruses and
(e.g. dUTPase) suggests gene capture events during evolution aviadenoviruses suggest viral gene swapping positions within the
(Davison et al., 2003). Furthermore, the presence of paralogous viral genomes or separate gene capture events from host genes
ORF clusters is thought to have been originated by duplication during evolution (Ojkic and Nagy, 2000; Davison et al., 2003;
(Washietl and Eisenhaber, 2003). Such clusters in the aviadeno- Harrach et al., 2011). For example, the putative dUTPase (E4
virus genome include E4ORF6-like genes (ORFs 24 and 14), ORF1) and E4ORF6 are located within the E4 region at the
parvovirus NS-1 homologues (ORFs 2, 13 and 12), the putative right end of the mastadenovirus genome (Weiss et al., 1997),
type-1 transmembrane glycoproteins (ORFs 9, 10, 11) with an whereas their homologues in aviadenovirus (ORF1 and ORFs
immunoglobulin-like domain and ORF19 (Washietl and Eisen- 24 and 14, respectively) map at the left end region (Chiocca et
haber, 2003; Corredor et al., 2006, 2008; Gilson et al., 2016), or al., 1996; Ojkic and Nagy, 2000). FAdV-9 ORF1 has functional
E4 34 K and HR homologues in atadenoviruses (Harrach et al., dUTPase activity (Deng et al., 2016), whilst this function is
2011). The ORF content within the paralogous clusters seems lacking in adenovirus E4ORF1 (Weiss et al., 1997). Similarly,
to influence the genome size and gene content, as is the case Gam-1 (ORF-8) and ORF22, located at the right end of the avia-
for FAdVs. The extent of duplication and gene content seem denoviral genome, are functionally equivalent to the E1 genes of
to contribute to the genome size of some aviadenoviruses. For mastadenoviruses, which are located at the left end (Lehrmann
example, the size of the left end region of FAdV-1 is smaller and Cotten, 1999).
than that of most aviadenoviruses. While one E4ORF6-like The origin of siadenoviruses is still not known, but they seem
gene (ORF14) is present in FAdV-1, five ORF14 homologues to have adapted to avian species later. Atadenoviruses are believed