Patuxent Wildlife Research Center
Effects of Agricultural Pesticides on Translocated Tadpoles of the Pacific Treefrog in Lassen, Yosemite, and Sequoia National ParksDeborah F. Cowman1, Donald W. Sparling2, Gary M. Fellers3, and Thomas E. Lacher1
1Wildlife and Fisheries Sciences Department, Texas A&M University, College Station, TX
2USGS Patuxent Wildlife Research Center, Laurel, MD
3USGS Western Ecological Research Center, Point Reyes National Seashore, Point Reyes, CA.
ABSTRACTIn recent studies chemical analyses show that highest levels of contaminants in surface water and dry particulate samples in the Sierra Nevada Mountains, CA are pesticides applied in the Central Valley, CA during heavy use periods in summer. Don Sparling, Gary Fellers, and Laura McConnell (2001) have recently found significant levels of pesticides (chlorpyrifos, diazinon, and endosulfan) in tissues of adult Pacific treefrogs, Hyla (Pseudacris) regilla, (Silva 1997) collected in the Sierra Nevadas.
This study tests the null hypothesis that pesticides are not having adverse effects on H. regilla tadpoles. H. regilla tadpoles were translocated in cages among sites located in Lassen, Yosemite, and Sequoia National Parks, and held in place to metamorphosis. Suspected impacts to be evaluated include: (1) increased mortality of larvae due to direct toxicity, cholinesterase (ChE) inhibition, or physical malformations; (2) reduced survivorship of tadpoles; (3) increased percentages of malformations at metamorphosis; (4) increased genetic damage in exposed larvae (measured by flow-cytometry); and (5) elevated body burdens of pesticides and ChE inhibition.
Discovery of detrimental effects in Pacific treefrog larvae and newly metamorphosed frogs may provide significant information towards the evaluation of ranid amphibian declines in the Sierra Nevada Mountains.
INTRODUCTIONBroad scale field sampling compared with historical analyses of museum records shows an ecosystem level decline of amphibians in the Great Central Valley in California. Counties most affected are Sacramento and those of the San Joaquin Valley (Fisher and Shaffer 1996). The collapse of a regional frog fauna, 5 of 7 species, in the Yosemite area of the California Sierra Nevada, has also been documented (Drost and Fellers 1996). Jennings (1996) reported that all 5 native ranid species in the Sierra Nevada are in need of protection. The Cascade frog (Rana cascadae) is in serious decline and the northern leopard frog (R. pipiens) has disappeared from 99% of its range (Jennings and Hayes 1994). The California red-legged frog (R. aurora draytonii) is listed as threatened (Miller 1994). The foothill yellow-legged frog (R. boylii) is in decline (Drost and Fellers 1996) and the mountain yellow-legged frog (R. muscosa) has disappeared from over 75% of study sites where it was formerly found in California (Bradford 1991, Bradford et al. 1994).
H. regilla was chosen as a surrogate species for testing because ranid frog numbers are seriously low. This treefrog species occurs in the same areas as the ranids and is widespread and abundant. However, their exposure to water is much less than that of ranid frogs and this may help to explain why they are still abundant in areas of ranid frog declines. If adverse effects of pesticide exposure is found in H. regilla, ranid frogs may be undergoing similar effects at an increased rate based on length of exposure.
OBJECTIVESWe propose to test the null hypothesis:
Possible impacts to be evaluated include: (1) increased mortality of larvae due to direct toxicity, cholinesterase (ChE) inhibition, or physical malformations; (2) reduced survivorship of tadpoles; (3)increased percentages and type of malformations at metamorphosis; (4) genetic damage in larvae and adults; and (5) elevated body burdens of pesticides and ChE inhibition.
Phase 1Prior to tadpole translocations, sampling transects will be established from coastal to mountain locations (see map below).
H. regilla tadpoles, adult males, sediment, and water will be collected along transects at 3 sites per location (red dots indicate locations).
Residue analyses will be conducted on all samples; ChE analyses will also be done on tissues.
Broadscale sampling will (1) provide a baseline of information for the study; (2) will enable us to more clearly define trends in pesticides levels and effects from coastal to mountain areas; and (3) aid in our interpretation of translocation data.
Phase 2Tadpoles (Gosner stage 21-25) were translocated among each of the 3 parks (June 1-Sept.7, 2001).
Tadpoles were held in place in a field-tested design cage (Harris and Bogart 1997)made of Nitex® nylon (see diagram below).
Tadpoles were fed boiled romaine lettuce, and sampled at 28 days exposure
and at metamorphosis (Gosner stage 45-46).
Criteria for site selection (Fall 2000):
Each pond selected held 9 cages, 3 cages containing tadpoles per each
park (27 cages per park)
Preliminary Results Phase 2Survivorship of tadpoles to metamorphosis was greatest at Lassen Volcanic National Park
Malformations of hind limbs, brachymelia, (first segment of hind limb truncated; see photo below) observed in tadpoles and newly metamorphosed frogs at all three parks.
LITERATURE CITEDBradford, D.F. 1991. Mass mortality and extinction in a high-elevation population of Rana muscosa. Journal of Herpetology 25:174-177.
Bradford, D.F., Graber, D.M. and Tabatabai, F. 1994. Population declines of the native frog, Rana muscosa, in Sequoia and Kings Canyon National Parks, California. Southwestern Naturalist 39:323-327.
Drost, C.A. and Fellers, G.A. 1996. Collapse of a regional frog fauna in the Yosemite area of the California Sierra Nevada, USA. Conservation Biology 10:414-425.
Fisher, R.N. and Shaffer, H.B. 1996. The decline of amphibians in Californias Great Central Valley. Conservation Biology 10:1387-1397.
Harris, M.L. and Bogart, J.P. 1997. A cage for evaluation of in situ water quality using frog eggs and tadpoles. Herpetological Review 28:134-135.
Jennings, M.R. 1996. Status of Amphibians. Sierra Nevada Ecosystem Project: Final Report to Congress, volume IIAssessments and Scientific Basis for Management Options. Report 37. University of California Davis, Davis, CA. USA.
Jennings, M.R. and Hayes, M.P. 1994. Amphibian and reptile species of special concern in California. Rancho Cordova: California Department of Fish and Game, Inland Fisheries Division.
Miller, K.J. 1994. Endangered and threatened wildlife and plants: Proposed endangered status for the California red-legged frog. Federal Register 59, no.22 (2 February): 4888-95.
Silva, H.R. 1997. Two character states new for hylines and the taxonomy of the genus Pseudacris. Journal of Herpetology 31:609-613.
Sparling, D.W., Fellers, G.M. and McConnell, L.L. 2001. Pesticides and Amphibian Population Declines in California, USA. Environmental Toxicology and Chemistry: 20:1591-1595.
ACKNOWLEDGMENTSThis study is the result of collaboration among investigators and resource managers from USGS, USDA-ARS, Texas A&M University, USFWS, and NPS. Many thanks to all who have contributed advice and logistical help in the planning of this project. Special thanks to field technicians: Erika Cowman, Shenandoah Marr, Deborah Purce, and Pamela Widder, and to Patrick Kleeman, USGS Western Ecological Research Center, Point Reyes National Seashore, Point Reyes, CA, for all his help in the field.
Maps of California were made by Carlos Hinojosa and Amy Hays of the Land Information Systems, Texas A&M University.
Funding is provided for this study by USGS, Amphibian Research and Monitoring Initiative and USFWS, Endangered Species, Region 1.
U.S. Department of the Interior
Patuxent Wildlife Research Center, Laurel, MD, USA 20708-4038
Contact: Deborah Cowman, email: Deborah_Cowman@usgs.gov
Last Modified: 03/20/02
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