Global Amphibian Decline: Disease

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: http://www.amphibianark.org/chytrid

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

Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. Lips et al., 2006. Science

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

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

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

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

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

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

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

Observations and Results No Chytrid detected initially at site (1998-2004) 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

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

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

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

The Effect of Trematode Infection on Amphibian Limb Development and Survivorship Johnson et al., 1999. Science

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!

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

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

Study Design/Methods (Field Study) Surveyed 36 ponds (1996-1998) Looked for deformed frogs Tested water for contaminants (PCBs,heavy metals)

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)

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)

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

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.

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

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

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!

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

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. 2006. 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. 1999. Limb Development and SurvivorshipThe Effect of Trematode Infection on Amphibian. Science, 284, 802-804. http://www.amphibianark.org/chytrid