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Presented at the NABS Annual meeting, Anchorage, Alaska, 2006
in Life Histories
Nitrogen and Carbon Stable Isotope Kinetics in the Life-Cycle of the Black Fly, Simulium vittatum IS-7
J.P. Overmyer1, M.A. MacNeil2, and A.T. Fisk3.1Department of Entomology, University of Georgia, Athens, Georgia, USA 30602, 2Department of Marine Science and Technology, University of Newcastle, Newcastle upon Tyne, UK, NE1 7RU, 3Warnell School of Forest Resources, University of Georgia, Athens, Georgia, USA 30602
Stable isotopes (SI) of nitrogen (δ15N) and carbon (δ13C) have become a commonly used tool to assess feeding ecology of organisms. This method assumes that δ15N increases, at approximately 3.4 ‰ per trophic level, but that δ13C is conserved between trophic levels. These assumptions are often found to be inaccurate and to vary among organisms. An additional assumption is that SI-turnover after a low to high SI diet switch and SI turnover after a high to low SI diet switch (elimination) will occur at the same rate. To address these assumptions, we conducted feeding studies with black fly (Simulium vittatum IS-7) larvae using diets that varied in SI values. Values of δ15N in black fly larvae were lower than those in food in all experiments; contrast to expected enrichment assumed in most studies. Head capsules collected from molting individuals were enriched in δ15N, which may in part explain this depletion. Emerging adults were enriched in δ15N compared to larvae but still depleted compared with food. Values of δ13C values were consistent through all experiments and showed a slight enrichment of δ13C among larvae, adults and their food.
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