1. Causes of amphibian decline
Presented by Heather Farnden

2. What are the causes of amphibian decline?
Natural fluctuations
Anthropogenic causes
Have the studies been able to demonstrate why?
Reasons supporting causes
What can we do about it?
What direction should research take?

3. -Anderson, J.D., Hassinger, D.D., and Dalrymple, G.H. 1971
Variation in larvae survivorship and developmental rate attributed to local conditions
-Anderson, J.D., Hassinger, D.D., and Dalrymple, G.H. 1971
Natural mortality of eggs and larvae of Ambystoma t. tigrinum
Ecology 52:
Attempted to correlate observed mortality with various factors such as temperature, pH and predation

4. Some studies looked at amphibian response to chemicals
-Cooke, A.S. 1973
Response of Rana temporaria tadpoles to chronic doses of pp#-DDT
Copeia 1973:
-Weis, J.S. 1975
The effect of DDT on tail regeneration in Rana pipiens and R. catesbeiana tadpoles
Copeia 1975:

5. Tadpoles as indicators of harmful levels of pollution in the field
-Cooke, A.S.1981
Tadpoles as indicators of harmful levels of pollution in the field
Environmental Pollution 25A:
-mortality, growth, rate of metamorphosis and occurrence of deformities
Decline in amphibian populations is reported at the First World Congress of Herpetology held in Canterbury England

6. Several suggestions put forward as to reason for declines
Climate change
UV-B radiation
Infection
Habitat loss
Pollution
Introduced species

7. Blaustein, A.R., Hokit, D.G., O’Hara, R.K. and Holt., R.A. 1994
Pathogenic fungus contributes to amphibian losses in the Pacific Northwest
Biological Conservation 67:
Blaustein, A.R., Hoffman, P.D., Hokit, D.G., Kiesecker, J.M., Walls, S.C., and Hays, J.B. 1994
UV repair and resistance to solar UV-B in amphibian eggs: A link to population declines?
Proc. Nat. Acad. Sci. 91:
Kiesecker, J.M. and Blaustein, A.R. 1995
Synergism between UV-B radiation and a pathogen magnifies amphibian embryo mortality in nature
Proc. Nat. Acad. Sci. 92:

8. Carey, C. and Bryant, C.J. 1995
Possible interrelations among environmental toxicants, amphibian development, and decline of amphibian populations
Environmental Health Perspectives 103: 13-17
Berger, L. et al 1998
Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America
Proc. Nat. Acad. Sci. 95:
Pounds, J.A., Fogden, M.P.L., and Campbell, J.H. 1999
Biological response to climate change on a tropical mountain
Nature 398:

9. The effect of trematode infection on amphibian limb development and survivorship
Pieter T.J. Johnson, Kevin B. Lunde, Euan G. Ritchie, and Alan E. Launer
Science. 284: (1999)

10. Pacific treefrog - Hyla regilla
Photo by Chris Brown
Is Ribeiroia infection responsible for the limb abnormalities observed in H. regilla?

11. Observations
Survey of ponds found that 4 of 13 ponds with H. regilla had high incidence of frogs with hindlimb abnormalities
Water tests excluded pesticides, PCBs, or heavy metals
Eggs hatched in lab setting were normal
These 4 ponds also had the snail Planorbella tenuis (first host of trematode Ribeiroia sp.)

12. Asexual reproduction of parasite in snails
Cercariae (free swimming) released - infect frog larvae
Encyst around developing limbs Metacercariae (resting stage)
Birds such as heron consume infected frogs - Parasite eggs released in feces
Eggs hatch - Miracidia infect the snails

13. Methods
H. regilla egg masses were collected where abnormalities unknown
Individually placed in 1 L container with commercial springwater after hatching
Tadpoles were assigned to a specific treatment and then exposed to the parasites in four equal doses over 10 days with each dose equivalent to 1/4 of the total parasite load

14. Randomly assigned to one of the following treatments:
1. Control ( 0 Reibeiroia cercariae)
2. Light (16 Reibeiroia cercariae)
3. Intermediate (32 Reibeiroia cercariae)
4. Heavy (48 Reibeiroia cercariae)
5. 80 Alaria mustelae cercariae
6. Mixed 80 Alaria mustelae and 32 Reibeiroia cercariae

15. Control group showed 88% survivorship and 0% abnormal limb development
Findings
85% of frogs that survived to metamorphosis developed hind limb abnormalities
Tadpole survivorship fell below 50% with intermediate and heavy treatments
Control group showed 88% survivorship and 0% abnormal limb development

16. Abnormality frequency
Survivorship to metamorphosis
Increased density of Ribeiroia cercariae leads to: increased abnormal limb development and decreased tadpole survivorship

17. Solid - survivorship
Clear - abnormality frequency
Shows that Alaria has no effect on survivorship or on limb deformities

19. Complex causes of amphibian population declines
Joseph M. Kiesecker, Andrew R. Blaustein & Lisa K. Belden
Nature. 410: (2001)

20. Western toad - Bufo boreas
Photo by Chris Brown
How are variability in precipitation, UV-B exposure and infection by the pathogenic fungus Saprolegnia ferax linked to amphibian decline?

21. Predictions:
Mortality associated with S. ferax infections at natural ovipostion sites is related to the water depth in which embryos develop;
Water depth at an ovipostion site is a function of variability in precipitation associated with ENSO cycles; and
Outbreaks of S. ferax infections observed in shallow water are mediated by exposure to UV-B radiation

22. Methods Measurements of mortality at ovipostion sites
Number of eggs estimated (breeding pairs x eggs per female)
Measurement of water depth to top of egg mass on four separate dates. (Standardized and averaged)
S. ferax infected eggs are covered in visible white hyphae and do not hatch
1m2 grid with 0.1m2 squares - count of number of dead and healthy eggs per square - average over grid estimate of mortality in five randomly assigned locations

23. 50 times at each site eggs removed and dead and healthy eggs counted - averaged for per cent mortality at that site (1998 and 1999)
Compared summer SOI and winter precipitation in the north Cascade Mountains of Oregon

24. Field experiment
Lost Lake, Linn County, Oregon - May 15 to May 29, 1996
Ten eggs from ten clutches were placed in each enclosure
Enclosures were opaque plastic with 500 m mesh floors allowing water flow and S. ferax transmission

25. Enclosures were covered with a UV-B blocking filter or acetate (80% UV-B transmitting)
Placed at 10, 50 or 100 cm depth
Temperature recorded 6 times per hour at three enclosures at each depth
UV-B levels measured every 5 cm to 100 cm

26.
The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

27. Relationship between summer SOI and winter precipitation in the north Cascade Mountains (1989-1999)
Negative SOI is associated with El Niño - below average precipitation in the Pacific Northwest during the following winter

28. Relationship between winter precipitation ( ) and water depth at oviposition sites during embryonic development
Depth during embryonic development increases as precipitation increases

29. Relationship between water depth during embryonic development and S
Relationship between water depth during embryonic development and S. ferax-associated mortality
Higher percentage of embryos hatch when development takes place in deeper water

30. Depth increased survival to hatching
UV-B radiation decreases as depth increases
Open - UV-B blocked
Closed - UV-B transmitted

31. Conclusions
Both papers have established that infection can cause population declines in amphibians
Johnson et al suggest that eutrophication may increase incidence of infection
Kiesecker et al have forged the link between infection and climate-related factors

32. Directions
Further research into complex causes needs to be done to make connections between local, regional and global declines in amphibian populations
Understanding the reasons may help initiate the solutions to eradicate population declines

33. The end