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Stable Isotopes as a Tool for Marking Amphibians

David Scott, Yurena Yanes, Betsie Rothermel, Melissa Pilgrim, and Chris Romanek


Stable isotope techniques have been used to understand dispersal of animals at different scales. For example, 15N addition to wetlands has been used to mark millions of insect larvae and subsequently determine dispersal patterns via captures of 15N -enriched adults at non-enriched sites. Understanding the extent of dispersal among wetlands is similarly important for conservation of pond-breeding amphibians, which function as metapopulations that are spatially disjunct and dependent on immigration for persistence. We conducted a pilot study using 15N enrichment of the aquatic habitat, thereby “marking” metamorphic amphibians. Because newly metamorphosed amphibians may not be recaptured until adulthood one or more years later, we sought to determine whether 15N enrichment would persist to sexual maturity. Marbled salamanders (Ambystoma opacum Gravenhorst) were reared in artificial mesocosms enriched with 15N H4Cl (0.217 g/m2). Initial doses to larvae resulted in δ15N levels in metamorphs elevated >1000 times above controls (4.76 ± 0.45 ‰). Metamorphs were held in the laboratory for up to seven months and fed on non-enriched crickets; juvenile 15N levels were determined at 1 mo and 7 mo post-metamorphosis to estimate the biological half life (BHL) of 15N. Seven months after metamorphosis, δ15N remained high (1800 ‰) in salamanders from the spiked treatment, approximately 225 times controls. The mean BHL for δ15N in the 15N -added treatment was 3.67 ± 0.19 months. Therefore, our BHL estimates suggest that the enrichment technique is feasible for amphibians, as metamorphs will leave isotopically enriched sites with a stable isotope signature that will persist for at least two years.

ACKNOWLEDGEMENTS:We would like to thank Angie Tucker for help with feeding and rearing metamorphs. Research was partially supported by the Department of Energy under Award Number DE-FC09-07SR22506 to the University of Georgia Research Foundation.

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