Saturday, 5 January 2013

Lethal Effects of Water Quality on Threatened California Salamanders but Not on Co-Occurring Hybrid Salamanders – via Herp Digest


Conservation Biology
Early View (Online Version of Record published before inclusion in an issue)
MAUREEN E. RYAN1,*,
JARRETT R. JOHNSON2,
BENJAMIN M. FITZPATRICK3,
LINDA J. LOWENSTINE4,
ANGELA M. PICCO5,
H. BRADLEY SHAFFER6

1Department of Evolution and Ecology, and Center for Population Biology, University of California, Davis, CA, U.S.A
2Department of Biology, Western Kentucky University, Bowling Green, KY, U.S.A
3Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, U.S.A
4Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, CA, U.S.A
5United States Fish and Wildlife Service, Pacific Southwest Regional Office, Sacramento, CA, U.S.A
6Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Room LS5120, Box 951606, Los Angeles, CA 90095 & La Kretz Center for California Conservation Science, Institute of the Environment and Sustainability, La Kretz Hall, Suite 300, Box 951496, 619 Charles E. Young Drive East, University of California, Los Angeles, CA, U.S.A
*Current address: Department of Civil & Environmental Engineering, University of Washington, 201 More Hall, Box 352700, Seattle, WA 98195, U.S.A. emails moryan@u.washington.edu, ambystomo@gmail.com
Article first published online: 9 NOV 2012
DOI: 10.1111/j.1523-1739.2012.01955.x

Abstract
Biological invasions and habitat alteration are often detrimental to native species, but their interactions are difficult to predict. Interbreeding between native and introduced species generates novel genotypes and phenotypes, and human land use alters habitat structure and chemistry. Both invasions and habitat alteration create new biological challenges and opportunities. In the intensively farmed Salinas Valley, California (U.S.A.), threatened California tiger salamanders (Ambystoma californiense) have been replaced by hybrids between California tiger salamander and introduced barred tiger salamanders (Ambystoma tigrinum mavortium). We conducted an enclosure experiment to examine the effects habitat modification and relative frequency of hybrid and native California tiger salamanders have on recruitment of salamanders and their prey, Pacific chorus frogs (Pseudacris regilla). We tested whether recruitment differed among genetic classes of tiger salamanders (hybrid or native) and pond hydroperiod (seasonal or perennial). Roughly 6 weeks into the experiment, 70% (of 378 total) of salamander larvae died in 4 out of 6 ponds. Native salamanders survived (n = 12) in these ponds only if they had metamorphosed prior to the die-offs. During die-offs, all larvae of native salamanders died, whereas 56% of hybrid larvae died. We necropsied native and hybrid salamanders, tested water quality, and queried the California Department of Pesticide Regulation database to investigate possible causes of the die-offs. Salamander die-offs, changes in the abundance of other community members (invertebrates, algae, and cyanobacteria), shifts in salamander sex ratio, and patterns of pesticide application in adjacent fields suggest that pesticide use may have contributed to die-offs. That all survivors were hybrids suggests that environmental stress may promote rapid displacement of native genotypes.

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