1. Global Amphibian Decline: Disease

2. Global Amphibian Decline
Amphibian populations declining worldwide
43% of species have declined
Mass species extinctions
30% of amphibian species listed as “threatened with extinction”
Source:

3. Global Amphibian Decline
Multiple Causes
-Disease (Chytrid Fungus)
-Habitat Loss (development)
-Pollution/Chemicals
-Climate Change
-‘Enigmatic’ (cause unknown)

4. Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. Lips et al., Science

5. Disease Ecology Theory
Formerly thought Disease-Caused Species Extinctions RARE
Increased infection = decreased transmission
Susceptible hosts die, resistant hosts persist
= loss of susceptible hosts
Pathogen extinction before host extinction

6. New Work Suggests… Disease/Pathogens CAN cause extinctions Requires:
-Abiotic + Biotic Reservoirs
-Multiple Hosts (Disease Vectors)
-Small Host Population Sizes

7. Can disease lead to species extinctions and loss of biodiversity in a vertebrate community?

8. Chytrid Fungus: An emerging infectious disease
Batrachochytridium dendrobatidis (Bd)=Fungus Species
Causes “chytridiomycosis” (the disease)
Affects amphibian skin

9. Questions
Is chytridiomycosis (chytrid) correlated to decreasing abundance and species richness?
Is chytrid moving in “epidemic wave” North to South across Central America?

10. Study Site: El Cope, Panama
Lips et al.,Science

11. Study Design/Methods Terrestrial and stream Surveys Captured Adults
Measured Species Richness + Density
Tested for presence of Bd in skin samples and environmental swabs
-Histological Exams, PCR

12. Observations and Results
No Chytrid detected initially at site
( )
Sudden Increased Mortality and Decreased Density
(post-Sept 2004)
-346 Dead Frogs; Almost all infected with Bd
- 47/67 species infected (70%)
- 6/7 environmental swabs positive for Bd

13. Observations: Decrease Abundance Increase Mortality
Decrease Species Richness
Density
Mortality
Species Richness
Lips et al.,Science

14. Chytrid: An ‘Epidemic Wave”?
Many species +
Long infectivity period +
(infection without death)
Biotic and Abitoic Reservoirs =
(water bodies and frogs)
Saturation of Environment with Zoospores (frogs and water)
Followed by…
Mass Mortality/Loss of Species

15. Conclusions:
Chytrid likely cause of mass mortalities observed at El Cope study site
(no evidence at site of other possible causes)
Results consistent with epidemic spread of chrtryid N to S across Central America
Evidence shows disease CAN decrease biodiversity in vertebrate community

16. The Effect of Trematode Infection on Amphibian Limb Development and Survivorship Johnson et al., Science

17. Amphibian Deformities: Why are they Important?
Abnormalities seen in 36 amphibian species in US
Not known if contributing to global amphibian decline
Not known if deformities reflect environmental disturbances that could harm human health
Cause of Deformities UNKNOWN!

18. Questions
Is parasite infection cause of Frog limb abnormalities observed in Wild?
Is limb deformity a contributing factor to global amphibian declines?

19. Study Site and Background
Location: Santa Clara Country, California
Species: Pacific Treefrog (Hyla regilla)
Parasite: Ribeirioa sp. (a trematode flatworm)
Aquatic Snail Host: Planorbella tenuis

20. Study Design/Methods (Field Study)
Surveyed 36 ponds ( )
Looked for deformed frogs
Tested water for contaminants (PCBs,heavy metals)

21. Study Design/Methods (Lab Study)
Collected Frog eggs from site with no reported/observed deformities
Reared tadpoles and exposed them to parasite cercariae (free-swimming larval form)

22. Parasite Treatments 1 – Control (no parasite) 2 – Light (16 Ribeirioa)
3 – Moderate (32 Ribeirioa)
4 – Heavy (48 Ribeirioa)
5 – 2nd parasite (Alaria)
6 – Combo (80 Alaria + 32 Ribeirioa)

23. Results and Observations (Field)
4/13 ponds with PTF, abnormalities were seen
**** 4 ponds were only ones with both PTF
and snail host
Dissected frogs (w/deformities) had Ribeirioa concentratred around hindlimbs
No biocides detected from water tests

24. Results and Observations (Lab)
Solid Line = survivorship
Dashed Line =Abnormality Freq.
Ribeiroia exposure caused abnormalities in 85% of surviving tadpoles
Positive relationship btw/ abnormality frequency & parasite density (dashed line)
Negative relationship btw/ tadpole survivorship & parasite density (solid line)
Black Bar = survivorship
White Bar =Abnormality Freq.
Johnson et al. 1999, Science.

25. Results and Observations (Lab)
Control Group (no parasite)
88% survived; all developed normally
‘Heavy’ Parasite Treatment
40% survived; ALL had abnormalities

26. Types of Abnormalities Observed
Missing, Extra and Deformed Hind Limbs
Johnson et al. 1999, Science.

27. Conclusions
Ribeirioa likely cause of abnormalities observed in field study
Trematode infection represents a considerable sources of mortality in some amphibian populations
More research needed on parasite infection and its role in amphibian abnormalities and declines!

28. Why Should We Care About All This?
Amphibians are our
“Canaries in the Coal Mine”

29. References
Lips, K R., Brem F., Brenes, R., Reeve, J. D., Alford, R. A., Voyles, J. , Carey, C., Livo, L., Pessie, A. P., and Collins, J. P Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. PNAS, 103(9), 3165–3170.
Johnson, P. T. J., Lunde, K. B., Ritchie, E. G., and Launer, A.E Limb Development and SurvivorshipThe Effect of Trematode Infection on Amphibian. Science, 284,