Transcript Amphibians: Indicators of Environmental Conditions

Amphibians: Indicators of
Environmental Conditions
Michael Ellefson
Joe Ryan
Why a good indicator?
• Amphibians breath through their skin,
which allow toxins/chemicals to be
absorbed into their body
Overview
• Salamander
Population Decline
– Rising levels of Acid
Deposition
– Rising levels of Pesticides
(TPT in particular)
– Habitat Loss
– Rising occurrences of
Viruses (Particularly RRV
ATV)
– Rise in levels of Heavy
Metals (Particularly
Cadmium)
• Decline in Frog
Populations
– Ultraviolet Radiation
– Rising occurrences of
Parasites (Particularly
Ribeiroia)
– Rising levels of Pesticides
(Particularly Atrozine and
Methoprene)
Acid Deposition: General
Information
• Acid deposition includes acid
rain, fog, and snow and acidic
gases and particles.
• Primary causes of acid rain are
the increases in Sulfur Dioxide
and Nitrogen Oxides
• 2/3 of Sulfur Dioxide and ¼ o
Nitrogen Oxides comes from
electric power generation that
relies on burning fossil fuels
Sulfur Dioxide and Nitrogen Oxides
• Nitrogen Oxides
– Why worry about it?
– Causes respiratory
illnesses in humans
– Sulfur Dioxide
– Why Worry?
– Causes respiratory
illnesses and
aggravates existing
heart and lung disease
Effects of Increasing Acid Deposition on
Salamander Population
• During the last seven years,
the Tiger Salamander
(Ambystoma Tigrinum
nebulsun) of the Colorado
Rockies have declined in
population size by 65%
• A study showed that
salamander eggs had a LD-50
pH of 5.6, which is within the
range encountered by eggs at
the sites in the Rockies.
• Graph: pH levels of 6.1, 5.7,
5.3, and 4.9
TPT (Triphenyltin)
• Pesticide
• Tennessee State
University Study
showed that TPT
made natural killer
cells in humans to
become powerless in
their fight against
tumors and viral
onslaughts
• TPT and
Salamanders
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Study showed TPT causes mortality
and lower feeding rates in the
Streamside Salamander (Ambystoma
barbouri)
Lower feeding rates cause the
salamanders to metamorphosis later in
life, making the age of sexual maturity
later
Eggs exposed to 5 ug/L of TPT were
killed 93% of the time
Eggs exposed to 1 ug/L didn’t have any
mortality, but decreased their feeding
rate
Habitat Loss
•
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Professor James Petranka’s study
compared the number of
salamanders in habitats left
untouched by humans to habitats
that had had extensive logging of
trees
Of the estimated salamander
population in North Carolina, 80%
were found in streams passing
through undisturbed forests, while
20% were found in streams that
were next to developed land.
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The dramatic difference is thought
to be caused by fertilizer runoff
which increases the pH in the
waterways
Petranka estimates that 14 million
salamanders a year were killed in
North Carolina alone because of
habitat destruction
Iridoviruses: RRV and ATV
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Iridoviruses are known to infect
invertebrates, fresh and marine
fish, and amphibians
Regina ranivirus (RRV) was found
in salamanders in Vonda,
Saskatchewan
Ambystoma tigrinum (ATV) was
found in salamanders in
Southwestern United States
ATV and RRV were partly
responsible for a 77% decline in
the salamander population at
these two sites.
Symptoms of ATV and RRV
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•
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RRV- clinical symptoms include
loose feces, bloody stools,
anorexia, vomiting (sometimes
with blood), raised foci on skin,
and erosions
RRV-Post Mortem inspection;
affected all organ systems besides
the muscular and central nervous
system
ATV-reported that cells of the
epidermis, gills, and liver having
enlarged nuclear inclusions and
sloughed skin and mucus (weren’t
found in RRV)
Where did these new strains come
from?
• It is thought that old strains mutated and crossed species barrier
• Possible strains that could have mutated to form ATV and RRV
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Frog Virus 3 (FV3) found in frogs
IV29, found in meal worm
IV30, found in corn earworm
IV31, found in woodlice
IV22, found in black fly
Increase in Heavy Metals such as
Cadmium
• Low concentrations occur
naturally in environment
• Manure plants, metal
refineries, and pesticides
used on farms are major
sources of cadmium
increase
• Cadmium poses sever
implication for humans
• It causes diarrhea,
stomach pains, severe
vomiting, weakened
bones, infertility, damage
to central nervous
system, damage to
immune system,
psychological disorders,
and possibly DNA
damage or cancer
development
Cadmium and Amphibians
• LD-50 occurs at 227.3 • At levels of 12.8 mu
mu g/L Cd in less
g/L Cd, no mortalities
than 10 days and
were recorded, nor
193.1 mu g/L Cd in
were any restrictions
less than 24 hours in
on growth
salamander eggs
• During
Metamorphosis, these
concentrations
account for stunted
growth in the limbs
What can we do?
• Acid Deposition: use sulfur with less sulfer, washing the
coal before burning, using scrubbers which chemically
remove the sulfur dioxide, and burning natural gas
• Pesticides: Use less and use different types
• Habitat Loss: responsible development
FROGS
AND
FROG
DEFORMOTIES
• In 1995, a group of
children was playing
in Henderson,
Minnesota.
• That day, half of the
22 frogs they found
were deformed.
• Some had 5 or more
legs, no hind limbs,
and even lacked
eyes.
Frogs
• Malformations have been
reported in more than 60
species.
• Deformed frogs have
been found all over the
world, and 46 states in
the US.
• Every species naturally
has no more than 5%
deformities in their
populations. This statistic
is higher in frog
population.
Now, I know you’re all wondering
WHY?!?
• So, I’ll tell you all
about it.
• Possible Reasons:
– UV radiation
– Pollution (pesticides)
– Parasites
Ultraviolet Radiation
• Ultraviolet radiation
has been known to
disturb amphibian
development by
causing damage to
the immune system
and causing genetic
disorders. This has
been getting worse
with the decline of the
ozone layer.
• Ultraviolet rays can
kill amphibian
embryos, larvae, and
cause serious eye
damage in frogs.
However, this does
not explain the
deformities.
UV effects
• This graph shows the
mean population of
frog embryos
surviving to hatching
at different depths.
• Frogs in shallow
waters have a smaller
chance of surviving
because of the UV
rays.
POLLUTION
• Pesticide pollution was put
forth as a possible solution
because Retinoid, which is
similar to the pesticide
methoprene, plays an
important role in amphibian
development, even in hind limb
development. However, they
could not reporduce this with
methoprene.
• More recently, an
endocrinologist from Berkeley,
Tyrone Hayes, targeted
atrazine as a possible culprit.
• Atrazine is a weed killer. It has
been shown to chemically
castrate and feminize male
frogs.
• Many deformed frogs came
from atrazine contaminated
water.
Atrazine has also been known to
weaken frogs immune
systems, making them more
vulnerable to parasites.
Parasites
• Parasites, especially a
flatworm trematode called
Ribeiroia Ondatrae, explain
frog deformations better than
the other possible solutions.
• Ribeiroia forms cysts on the
body of frogs, especially
around the hind limbs, which
cause new legs to grow in
different places.
• Ribeiroia is almost always
found where frog deformities
are present, even where the
kids were playing in
Minnesota.
• It has now been identified in
WI, IL, PN, and NY.
Deformity Frequency and Ribeiroia
presence
• The frequency of
deformities rose in
relation to the
frequency of parasite
infections measured
in amphibians
dissected.
Ribeiroia Process
Rib makes frogs easy targets
•
Johnson et al. exposed
tadpole Pacific tree frog
(Hyla regilla) to the
cercaria of a trematode
parasite, Ribeiroia. They
found that as the number
of parasites per tadpoles
rises, the percentage of
abnormalities increases
while survival decreases.
Why does Rib attach to the back
legs?
• Hind limb malformations = 80% of total
malformations.
• They have remarkable accuracy of the
anatomical site where the penetrate their hosts.
They can even specify whether they are going to
infest the right or left side of the tadpole.
• The reason for this accuracy is that there is an
“arms race” between the parasite and the host.
After the parasite tries to infect the frog, the tries
to shake them loose through evasive action.
Rib attachment cont…
• So, the frog needs to attach to a place where it will be
able to hang on.
• High speed videography of staged encounters between
the parasite and host.
• Showed that frogs could more easily dislodge from sides
of tadpole.
• Conceptual fluid-dynamic models show that water in the
recess immediately behind the torso, next tail is
realatively stagnant. Called the “dead water zone.”
• Parasite attaches here because it decreases on water
drag, making it easier to hang on.
Deformed Tadpole
Synergistic deformities
• Pesticides and Ribeiroia
– As mentioned, pesticides weaken frog
immunity.
– This makes them less resistant to ribeiroia.
• This is because pesticides have been shown,
through models of locomotion, to reduce frog
activity. Reduced frog activity makes them more
vulnerable to parasites because they are less likely
to initiate fast, repetitive starts.
More about tadpole activity
• Frogs in the presence of predators, even
when separated by a screen, can
significantly increase the number of
parasites in the water.
• Tadpoles also reduce their activity in the
presence of predators, causing more
parasite infections.
The Human Factor
• Human impacts compound the effects of these three
natural factors.
• Destruction of ozone and UV rays
• Fertilizers such as nitrogen and phosphorus leak into the
water, causing algal blooms to become larger.
• This creates more food for snails, giving Rib more hosts
to infect.
• More fertilizers cause tadpoles to move around less
• Human stocking of ponds create more tadpole predators
• Majority of wetlands infected are artificial bodies of water
– Artificial bodies are more likely to be close to human influnce and
consequently more polluted.
Why should we care?
• Frogs occupy a very unique place in our
ecosystem.
• They are very sensitive to environmental
fluctuations because their respiration happens
through their skin. Their soft eggs are also very
sensitive
• Frogs are developing deformities now in places
and at rates unheard of in the past. The
potential that the frogs are a signal of things to
come is so great that answers must be found.