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Bird phylogenies and genomic fossils clarify the evolution of hepatitis B viruses

A new paper in Nature Communications that may be of interest:

Suh A, Brosius J, Schmitz J, Kriegs JO 2013 The genome of a Mesozoic
paleovirus reveals the evolution of hepatitis B viruses. Nature Comms
4(4): 1791

Paleovirology involves the identification of ancient endogenous viral
elements within eukaryotic genomes. The evolutionary origins of the
reverse-transcribing hepatitis B viruses, however, remain elusive, due
to the small number of endogenized sequences present in host genomes.
Here we report a comprehensively dated genomic record of hepatitis B
virus endogenizations that spans bird evolution from >82 to <12.1
million years ago. The oldest virus relic extends over a 99% complete
hepatitis B virus genome sequence and constitutes the first discovery
of a Mesozoic paleovirus genome. We show that Hepadnaviridae are >63
million years older than previously known and provide direct evidence
for coexistence of hepatitis B viruses and birds during the Mesozoic
and Cenozoic Eras. Finally, phylogenetic analyses and distribution of
hepatitis B virus relics suggest that birds potentially are the
ancestral hosts of Hepadnaviridae and mammalian hepatitis B viruses
probably emerged after a bird-mammal host switch. Our study reveals
previously undiscovered and multi-faceted insights into prehistoric
hepatitis B virus evolution and provides valuable resources for future
studies, such as _in-vitro_ resurrection of Mesozoic hepadnaviruses.

The viruses apparently first infiltrated their hosts' genomes shortly
after the galloanserine/neoavian split -- the corresponding "fossil"
is common to all sampled members of _Neoaves_. Interestingly, the
authors use Brown and van Tuinen's (2011) divergence time estimates,
which means that most of the dates they provide are pretty young in
comparison with other molecular analyses (e.g., the origin of
_Neoaves_ is dated at 82 Mya).


Brown JW, van Tuinen M 2011 Evolving perceptions on the antiquity of
the modern avian tree. 306-24 _in_ Dyke GJ, Kaiser G, eds. _Living
Dinosaurs: The Evolutionary History of Modern Birds_. London: John
Wiley and Sons

David Černý