what may represent a breathrough in the scientific exploration of
frog deformities, Sower et
al. report that deformed individuals of two species of wild
frogs in New Hampshire have abnormal concentrations of sex hormones
compared to normal individuals from the same region. These results
are consistent with the hypothesis that endocrine disruption is
involved in the genesis of frog deformities. The hormonal disruptions
reported by Sower et al. would not be expected to be associated
with deformities caused by parasites or predation.
on frog deformities to date has largely emphasized two approaches:
basic surveys to establish rates of deformities in different sites
and species, and efforts to identify factors present at those sites
which might cause deformities.
paper opens a new front on research, asking about the hormonal condition
of deformed frogs. It is analogous to the pathbreaking work by Dr.
Louis Guillette on alligators in Lake Apopka, Florida, with
miniature penises: much of Guillette's early work focused on establishing
that hormones in these alligators were wildly out of balance, which
then led to further experimental studies establishing that the imbalances
were caused by a cocktail of contaminants present in the lake.
et al. captured normal and deformed frogs of two species
(green frogs and bull frogs) from locations across central and southern
New Hampshire. They found deformed frogs at 81% of sites where they
caught 50 or more frogs. The percentage of frogs malformed varied
from 0 to 9.3% at a given site, while overall the total malformation
rate was 3.9%... 4.3% for bullfrogs and 2.4% for green frogs. [These
rates are low compared to collections reported in other places,
for example Minnesota
et al. examined two patterns of hormonal disruption in the
frogs: levels of gonadotropin-release hormone in the brain and the
amounts of androgens produced by testes and ovaries in an in
results are clear-cut: deformed frogs have lower concentrations
of gonadotropin-release hormones in the brain, and both male and
female gonads of deformed animals produce reduced androgens
two graphs (adapted from Sower et al.) compare normal
with deformed frogs in two measurements of hormone function:
the production of gonadotrophin-releasing hormone in the brain,
and production of androgens by the gonads. Both comparisons
reveal strong differences between normal and deformed animals.
to the authors, "Although chemical mechanisms cannot be ruled
out ... [these results] suggest that parasite infestation is not
the causal agent in our study.
significant decrease in GnRH (brain gonadotropin-releasing hormone)
correlated with depressed androgen concentrations and lack of proper
testicular morphology in malformed frogs provides evidence that
development of the neuroendocrine system may have been disrupted
during early frog development."