From: Science Alert
By David Nield
January 30, 2023 -- The genetic make-up of the iconic Australian black
swan (Cygnus atratus) leaves it extremely vulnerable to viruses such
as avian flu, research from the University of Queensland reports.
The threat is thought
to be so severe that it could wipe out the species entirely.
The discovery comes
after the distinctive bird's genome was sequenced for the first time in 2021.
Ordinarily, this
achievement would be something to celebrate from a scientific perspective – but
a comparison with closely-related northern hemisphere white swans has revealed
that certain key immune genes are missing from its DNA.
That's likely to be, at
least partly, down to the way that the black swan is isolated geographically.
These animals haven't had the same exposure to pathogens that are found outside
of southeast and southwest Australia, the areas where it primarily lives and
breeds.
"[B]lack swans are
extremely sensitive to highly pathogenic avian influenza – HPAI which is often
referred to as bird flu - and can die from it within three days," says
microbiologist Kirsty Short from the University of Queensland in
Australia.
"Our data suggests
that the immune system of the black swan is such that, should any avian viral
infection become established in its native habitat, their survival would be in
peril."
The team used powerful
computer software to compare the genes of the black swan with the
closely-related mute swan (Cygnus olor), found in the Northern
hemisphere. Tens of thousands of genes were compared in total in the search for
differences.
It was discovered that
a class of proteins in the toll-like receptor 7 (TLR7) family were not being
activated as they should. These parts of the genome have been associated
with protecting against bird flu and other pathogens.
In other words, the
gene for guarding against the bird flu virus is there, it's just not
being switched on when needed – and that puts the black swan under threat.
The team also
identified an unregulated inflammatory response to infection that could be
dangerous.
"We currently
don't have HPAI in Australia, but it has spread from Asia to North America,
Europe, North Africa, and South America. When it was introduced to new
locations, such as Chile and Peru, thousands of wild seabirds
perished," says Short.
During the course of
their research, the study authors also identified another gene – SLC45A2 – that
may be responsible for black swans being black rather than white.
In fact, as mutations
of this gene leads to loss of pigment – the same gene has previously been
linked to albinism in humans – it suggests the white swan is the newer variant,
and that the ancestral swans of both species were black.
The good news is that
knowing more about the vulnerability of these birds is going to help in efforts
to protect them. Either through selective breeding, or through immunotherapy
treatments, this TLR7 gap in the immune defenses could be filled.
Right now, the black
swan is one of the species that conservationists are least worried about,
with a population worldwide of up to a million. Those numbers could drastically
change in a short period of time, however.
"The risk to one
of Australia's most unique and beautiful birds is very real, and we need to be
prepared if we hope to protect it," says Short.
The research has been
published in Genome Biology.
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