ELEMENTAL COMPOSITION OF ENAMEL IN THE TEETH OF ADULT MARBLED SALAMANDERS, AMBYSTOMA OPACUM, FROM MIDDLE TENNESSEE

Abstract

Metals are deposited in the enamel of developing teeth in many groups of small vertebrates, including amphibians. For example, iron is a common constituent of enamel in many species of small vertebrates and often causes teeth to appear various shades of red. Although iron deposits in the teeth of small mammals have received considerable attention, several different lineages of salamanders, including ambystomatids, also sequester iron in the enamel of their teeth during amelogenesis. Furthermore, iron is present in the first set of teeth that develop in embryonic salamanders, before the individual is free-living or feeds. Because salamanders are polyphyodont, the amount of metals in their enamel presumably represents the amount accumulated since the previous set of teeth were replaced. Thus, the accumulation of a metal in the enamel of salamanders presumably is associated with the level of metals in the surrounding environment at the time when the most recent set of teeth was being formed. However, too little information is available to adequately address questions about metals, including iron, present in the teeth of salamanders. Here I examined elemental composition of teeth from a population of Marbled Salamanders (Ambystoma opacum). Specifically, I examined the types of metals sequestered in the enamel, and distribution and percentage of iron in the teeth of adults. Salamanders used in this study were collected as trap casualties from pits associated with a drift fence constructed at Arnold Air Force Base in Coffee County, Tennessee. The dead salamanders were fixed with 10% buffered formalin, transferred to 70% ETOH, and deposited in the Middle Tennessee State University Herpetology Collection. To perform elemental analysis, I removed the lower jaw from 10 individuals and separated the left and right halves of the lower jaw at the mental symphysis, removed soft tissue, and mounted each half to an aluminum stub using double stick tape. Furthermore, I used a dental pick to remove the crowns of three teeth from each specimen, and I mounted the excised crowns onto the same stub as the jaw from which they were removed. I used an Oxford INCA Energy 200 Dispersive analyzer synced to a Hitachi S-3400N scanning electron microscope to analyze the extent of Fe, and other trace elements, deposition by ameloblasts throughout the lingual cusp and shaft of the crown during formation of the enamel layer. To ensure that I was analyzing the same amount of area and penetrating the same depth of the enamel in each analysis, I used a magnification of 1,400X and an accelerating voltage of 15 kV for all readings. I analyzed six sites on each tooth, from the apex of the lingual cusp down to the base of the crown. Iron concentration was highest in the apex of the lingual cusp and diminished in a longitudinal fashion towards the base of the crown. In addition to Fe; Al, Cl, Cu, F, K, Mg, Na, S, Si, and W were also present in the enamel, but the mean weight percentage of each element varied among the sites indicating that their incorporation into the enamel was more haphazard than structural.