By Matt Walker
Editor, Earth News
Birds living around the site of the Chernobyl
nuclear accident have 5% smaller brains, an effect directly linked to lingering
background radiation.
The finding comes from a study of 550 birds
belonging to 48 different species living in the region, published in the
journal PLoS One.
Brain size was significantly smaller in yearlings
compared to older birds.
Smaller brain sizes are thought to be linked
to reduced cognitive ability.
The discovery was made by a team of researchers
from Norway, France and the US led by Professor Timothy Mousseau from the
University of South Carolina, US, and Dr Anders Moller from the University
of Paris-Sud, France.
Harmful legacy
In April 1986, reactor number four at the
Chernobyl Nuclear Power Plant exploded.
After the accident, traces of radioactive
deposits were found in nearly every country in the northern hemisphere.
An exclusion has since been set up around
the site of the accident.
However, scientists have been allowed inside
to gauge the impact the radiation has had on the ecology of the region.
Last year Prof
Mousseau and Dr Moller published the results of the largest wildlife
census of its kind conducted in Chernobyl - which revealed that mammals
are declining in the exclusion zone surrounding the nuclear power plant.
Scientist collecting bacteria samples in Chernobyl
The scientists have studied the exclusion zone for more than a decade
Insect diversity has also fallen, and previously,
the same researchers found a way to predict which species there are likely
to be most severely damaged by radioactive contamination, by evaluating
how often they renew parts of their DNA.
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In their latest study, the scientists used
mist nets to collect birds from eight woodland sites around Chernobyl,
which have seen a decline in the numbers of larger animals and small invertebrates
living within.
After controlling for the differences between
species, they found that the birds had brains 5% smaller on average compared
to birds not exposed to background radiation.
The effect was most pronounced in younger
birds, particularly those less than a year old.
That suggests that many bird embryos did not
survive at all, due the negative effects of their developing brain.
Mechanism unclear
Stressed birds are able to change the size
of some of their organs in order to tough out difficult environmental conditions.
For example, migrating birds that have travelled
long distances often shrink certain organs as they use up energy.
But the brain is the last organ to be sacrificed
in this way, say the researchers.
That suggests the background radiation could
be having an even more pronounced effect on other organs within the birds.
It is unclear exactly what mechanism is shrinking
the birds' brains.
High levels of background radiation cause
animals oxidative stress, where they have to use antioxidants in their
bodies to fight its ill effects.
That leaves animals exposed to radiation severely
depleted of antioxidants, and the reduced brain size may be a result of
this depletion.
Alternatively, radiation could cause developmental
errors in the way the brain grows.
However, if that were the case, the scientists
say they would expect to see pronounced changes to the size and shape of
other parts of the birds' bodies.
Another possibility is that the birds are
developing less well as there is less invertebrate prey for them to eat.
But the scientists know of no example of the
brains of a wild animal shrinking due to a lack of food. |
NUCLEAIRES !
