Introduction

Chytridiomycosis is an infectious disease that affects amphibians, and has been particularly harmful to certain species of frogs, and has in fact been 100% lethal for others. Scientists are dumbfounded by the somewhat sudden appearance of this fungal infection, and are not sure if this is a new fungus, or a newly virulent pattern for an old infection. Some researchers have suggested that global warming is contributing to the appearance and increased vitality of the fungus (1).

If global warming is contributing to the decline of certain species of frogs this may be due to the changes in the local climate in some regions, favoring the maturity and growth of chytrid fungi. As researchers determine more about the fate of the amphibians in the affected areas, they see that global warming has increased the evaporation in the region, which leads to an increased ability of the air to hold water. Next, this phenomena result in the increase of cloud cover. These facts help to reduce heat loss during the day as the clouds serve to radiate heat on the surface of the earth. Interestingly, these changes in the climate favor the growth of the fungus. To give credence to the threat of global warming, the appearance of the chytrid fungi could cause real disaster for my frog species that are currently affected (2).

One species of frog that is already extinct as a result of the chytrid fungus is the gastric-brooding frog, and the amphibian chytrid fungus is suspected to have caused some if not most of the declines of this species (3). While the fungus is generally highly pathogenic to amphibians, hosts express a wide range of responses to infection, probably due to variation among hosts and environmental conditions, but possibly also due to variation in Batrachochytriumdendrobatidis (Bd) (4). Although mortality in 3 groups of 15 green tree frogs Litoriacaerulea exposed to 3 isolates of Bd was 100%, time to death varied with isolate, highlighting the importance of strain and/or passage history in pathogenicity studies and possibly in the epidemiology of chytridiomycosis (5).

I feel these frogs were affected because of the environmental conditions that favored the growth of chytrid fungus in their area. Question: Could amphibians (frogs) in my area be affected by fungal species as well? I live in Bucks County, PA, and there is Silver Lake Park located there. Silver Lake provides refuge for the Redbelly Turtle and the marsh is home for the Coastal Plain Leopard Frog, known to scientists as Ranapipiens. I will be focusing on the effect of fungus on Ranapipiens. If fungus affects the frogs in a predatory manner, the frogs may become sick and die.

Most recently, scientists working independently in the United States and Australia have discovered a new fungus genus known as a chytrid fungus. It is believed to be killing frogs and toads around the world. There are still several unanswered questions about this latest discovery. It is known that this fungus has been found on dead frogs. However, it is unclear whether this fungus caused death or appeared after the frogs were weakened by some other agent, such as ultraviolet radiation damage. Additional research is needed to be certain.

Experiment

For this experiment, I wish to test the effect of the chytridfungus on Ranapipiens in my area. I will expose chytrid fungi to 10 frogs. For a control, I will use 10 Ranapipiens not exposed to the fungus. The constant variables will be the frogs themselves, and their environment. I will mark the 10 fungus exposed frogs with a special tag to identify them as part of the experiment. I will use a different colored tag to distinguish the non exposed frogs. I will observe these frogs in different areas of the park for 10 consecutive days and record any signs of sickness or death. I will ensure that the frogs are not unduly affected by any other agents during the time of my experiment. While this may not be entirely possible, I will do my best to measure the effects of just the chytrid fungus on the exposed frogs.

The predicted results of the experiment would be that the 10 exposed frogs will appear weaker, but will not die. This is likely because the species has not has enough time to react to the presence of the fungi. The affected frogs will probably just appear sickly; they will be less robust or active. The 10 non-exposed frogs will most likely appear as usual, with no sickness or loss of life.

Ranapipiens may be what some ecologists call, “an indicator species.” That means that the heath and survival of the frog is closely tied to the health of the environment. Based on the amount of media coverage some of the more recent issues involving frogs have received, there are reasons to be optimistic that the public is beginning to recognize that we as humans are linked to the health of frogs. Let's hope so. New experiments are needed to asses the health of the frogs in this area of the United States. Similar experiments to the one I had planned here may be used. I accept the results of my hypothesis and hope the harm to frogs may be averted.

References

  1. Pounds, J. Alan et al. (2006) "Widespread Amphibian Extinctions from Epidemic Deisease Driven by Global Warming." Nature 439.12 161-67
  2. Thomas, C.D.; Cameron, A.; Green, R.E.; Bakkenes, M.; Beaumont, L.J.; Collingham, Y.C.; Erasmus, B.F.N.; Siqueira, M.F.D.; Grainger, A.; Hannah, L. (2004). "Extinction risk from climate change" (PDF). Nature427 (6970): 145–148. doi:10.1038/nature02121. PMID14712274. Retrieved 2008-04-15.
  3. McDonald, K.R. 1990. RheobatrachusLiem and TaudactylusStraughan & Lee (Anura: Leptodactylidae) in Eungella National Park, Queensland: distribution and decline. Transactions of the Royal Society of South Australia 114(4): 187-194.
  4. Retallick, R., Miera, V. (2007) Strain differences in the amphibian chytridBatrachochytriumdendrobatidis and non-permanent, sub-lethal effects of infection. DisAquat Organ. 2007 May 9;75(3):201-7.
  5. Berger, L, Marantelli, G, Skerratt, LF, Speare, R. (2005) Virulence of the amphibian chytrid fungus Batrachochytiumdendrobatidis varies with the strain. DisAquat Organ. 2005 Dec 30;68(1):47-50.