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14 Is UV-B responsible for the amphibian decline?




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This article is from the Ozone Depletion: UV Radiation and its Effects FAQ, by Robert Parson rparson@spot.colorado.edu with numerous contributions by others.

14 Is UV-B responsible for the amphibian decline?

UV-B may be part of the story, although it is unlikely to be the
principal cause of this mysterious event.

During the past decade, there has been a widespread decline in
amphibian populations [Livermore] [Wake]. The decline appears to be
global in scope, although some regions and many species appear to be
unaffected. While habitat destruction is undoubtedly an important
factor, many of the affected species are native to regions where
habitat is relatively undisturbed. This has led to speculation that
global perturbations, such as pesticide pollution, acid deposition,
and climate change, could be involved.

Recently, [Blaustein et al.] have investigated the effects of UV-B
radiation on the reproduction of amphibians living in the Cascade
Mountains of Oregon. In their first experiment, the eggs of several
amphibian species were analyzed for an enzyme that is known to
*repair* UV-induced DNA damage. The eggs of the Cascades frog,
R. cascadae, and of the Western toad, Bufo Boreas, showed low levels
of this enzyme; both species are known to be in serious decline
(R. Cascadae populations have fallen by ~80% since the 1970's [Wake].)
In contrast, much higher levels of the enzyme are found in the eggs of
the Pacific Tree Frog, _Hyla Regilla_, whose populations do not appear
to be in decline.

Blaustein et al. then studied the effects of UV-B upon the
reproductive success of these species in the field, by screening the
eggs with a filter that blocks the ambient UV. Two control groups were
used for comparison; in one no filter was present and in the other a
filter that *transmitted* UV-B was put in place. They found that for
the two species that are known to be in decline, and that showed low
levels of the repair enzyme, filtering the UV dramatically increased
the proportion of eggs surviving until hatch, whereas for the species
that is not in decline and that produces high levels of the enzyme,
filtering the UV made little difference. Thus, both the laboratory and
the field experiments suggest a correlation between amphibian declines
and UV sensitivity, albeit a correlation that at present is based on a
very small number of species and a limited time period.

Contrary to the impression given by some media reports, Blaustein and
coworkers did *not* claim that ozone depletion is "the cause" of the
amphibian decline. The decline appears to be world-wide, whereas ozone
depletion is restricted to middle and high latitudes. Also, many
amphibian species lay their eggs under dense canopies or underground
where there is little solar radiation. So, UV should be regarded
as one of many stresses that may be acting on amphibian populations.

 

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