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29th Annual Meeting and Symposium of the
Desert Tortoise Council, February 20-23, 2004
Abstracts
A Laser Ablation ICP-MS Technique for Examining Elemental Distribution in Scute Tissues of Desert Tortoise Shells
1Michael D. Seltzer and 2Kristin Berry
1Naval Air Warfare Center Weapons Division, China Lake, CA,
USA 93555-6001
2U. S. Geological Survey, Western Ecological Research Center,
Moreno Valley, CA 92553
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a microanalysis technique capable of performing spatially-resolved measurements of elemental concentrations in a wide variety of solid samples. LA-ICP-MS has proven to be particularly useful for the examination of incrementally-grown biological structures such as teeth, mollusk shells, and fish otoliths. Patterns of elemental concentration, revealed in this manner, often exhibit seasonal periodicity as well as correlation with environmental and climatological change. The scutes on desert tortoise (Gopherus agassizii) shells offer an opportunity to evaluate elemental uptake chronologically. The growth rings on individual scutes consist of keratin in which various metals and metalloids are sequestered during early development and growth.
We tested three different approaches and ultimately determined that the ablation transects should be performed on the exposed lateral surfaces of sectioned scutes. This approach successfully avoids exogenous contamination from the scute exterior. Under these circumstances, the laser microprobe appears to encounter a succession of discrete laminae (e.g., from areola to the most recently produced ring), in order of deposition. Results obtained thus far indicate that patterns of zinc concentration provide a potentially useful "map" of the scute interior, as well as a spatial reference for the distribution of other elemental species. Patterns of arsenic concentration from scutes of tortoises ill with mycoplasmosis and cutaneous dyskeratosis exhibited distinct concentration maxima at specific locations along the laser ablation transect axis. The results presented here illustrate the utility of laser ablation ICP-MS techniques for providing analytical data having unique chronological aspect, a timeline implicit in the structures, and substantial diagnostic significance for the tortoise.
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