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

– 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

• 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.

• 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

• 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 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 mu g/L Cd in less than 10 days and 193.1 mu g/L Cd in less than 24 hours in salamander eggs

• During Metamorphosis, these concentrations account for stunted growth in the limbs

• At levels of 12.8 mu g/L Cd, no mortalities were recorded, nor were any restrictions on growth

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 wonderingWHY?!?

• 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.