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Amphibians Indicators of Environmental Conditions

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					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                      • Decline in Frog
  Population Decline                Populations
  – Rising levels of Acid           – Ultraviolet Radiation
    Deposition                      – Rising occurrences of
  – Rising levels of Pesticides       Parasites (Particularly
    (TPT in particular)               Ribeiroia)
  – Habitat Loss                    – Rising levels of Pesticides
  – Rising occurrences of             (Particularly Atrozine and
    Viruses (Particularly RRV         Methoprene)
    ATV)
  – Rise in levels of Heavy
    Metals (Particularly
    Cadmium)
          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             • TPT and
• Tennessee State         Salamanders
                          –   Study showed TPT causes mortality
  University Study            and lower feeding rates in the
                              Streamside Salamander (Ambystoma
  showed that TPT             barbouri)
                          –   Lower feeding rates cause the
  made natural killer         salamanders to metamorphosis later in
                              life, making the age of sexual maturity
  cells in humans to          later
  become powerless in     –   Eggs exposed to 5 ug/L of TPT were
                              killed 93% of the time
  their fight against     –   Eggs exposed to 1 ug/L didn’t have any
                              mortality, but decreased their feeding
  tumors and viral            rate

  onslaughts
                        Habitat Loss
•   Professor James Petranka’s study     •   The dramatic difference is thought
    compared the number of                   to be caused by fertilizer runoff
    salamanders in habitats left             which increases the pH in the
    untouched by humans to habitats          waterways
    that had had extensive logging of    •   Petranka estimates that 14 million
    trees                                    salamanders a year were killed in
•   Of the estimated salamander              North Carolina alone because of
    population in North Carolina, 80%        habitat destruction
    were found in streams passing
    through undisturbed forests, while
    20% were found in streams that
    were next to developed land.
       Iridoviruses: RRV and ATV
•   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
            •   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
    –   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     • Cadmium poses sever
  naturally in environment       implication for humans
• Manure plants, metal         • It causes diarrhea,
  refineries, and pesticides     stomach pains, severe
  used on farms are major        vomiting, weakened
  sources of cadmium             bones, infertility, damage
  increase                       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     • Ultraviolet rays can
  has been known to           kill amphibian
  disturb amphibian           embryos, larvae, and
  development by              cause serious eye
  causing damage to
  the immune system           damage in frogs.
  and causing genetic         However, this does
  disorders. This has         not explain the
  been getting worse          deformities.
  with the decline of the
  ozone layer.
                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      • More recently, an
  forth as a possible solution        endocrinologist from Berkeley,
  because Retinoid, which is          Tyrone Hayes, targeted
  similar to the pesticide            atrazine as a possible culprit.
  methoprene, plays an             • Atrazine is a weed killer. It has
  important role in amphibian         been shown to chemically
  development, even in hind limb      castrate and feminize male
  development. However, they          frogs.
  could not reporduce this with    • Many deformed frogs came
  methoprene.                         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.

				
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posted:5/5/2010
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