Meeting Abstract

68.10  Jan. 7  Incorporation and Isotopic Spacing of ¹³ C and ¹⁵N in a Rapidly Growing Ectotherm; Consequences of Growth and Tissue Type REICH, K.J.*; BJORNDAL, K.A.; MART�NEZ DEL RIO, C.; Univ. of Florida; Univ. of Florida; Univ. of Wyoming kreich@zoo.ufl.edu

Understanding the rate at which animals incorporate ¹³C and ¹⁵N isotopes from their diets and the factors that determine the magnitude of the difference in isotopic composition between the animal�s diet and its tissues is necessary to interpret stable isotope data accurately when investigating animal diet, habitat use, and trophic level. Both rate of isotopic incorporation (turnover) and isotopic spacing values (discrimination) can be affected by size of the animal, tissue type, rate of growth of that tissue, and nutrient composition of the diet. We determined the contribution of growth and catabolic turnover to the rate of ¹³C and ¹⁵N incorporation into skin, scute, whole blood, red blood cells, and plasma solutes in two age classes of a rapidly growing ectotherm (loggerhead turtles, Caretta caretta). We found significant differences in C and N incorporation rates and isotopic spacing among tissues and between age classes. Due to the significant contribution of growth to the rate of isotopic incorporation, variation in rates among tissues was lower than reported in previous studies. The isotopic spacing of nitrogen ranged from �0.64� to 1.77�, lower than the conventional 3.4�. Our results demonstrate that in rapidly growing ectotherms 1) the magnitude and constancy of incorporation rates vary among tissues; 2) physiological and ontogenetic status of an animal influence incorporation rates; 3) variance in incorporation rates among tissues is reduced in organisms undergoing rapid growth; and 4) isotopic spacing differs among tissues and is influenced by growth and diet.