Zoological Studies

Vol. 60, 2021

(update: 2021.03.18)
 

Tissue-specific Isotopic Incorporation Turnover Rates and Trophic Discrimination Factors in the Freshwater Shrimp Macrobrachium borellii (Crustacea: Decapoda: Palaemonidae)

María Florencia Viozzi1,*, Carlos Martínez del Rio2, Verónica Williner1,3

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1Laboratorio de Macrocrustáceos, Instituto Nacional de Limnología, Consejo Nacional de Investigaciones Científicas y Técnicas. E-mail: fviozzi@inali.unl.edu.ar (Viozzi)
2Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, United States of America. E-mail: CmDelRio@uwyo.edu (Martínez del Rio)
3Universidad Nacional del Litoral, Santa Fe, Argentina. E-mail: vwilliner@inali.unl.edu.ar (Williner)

Received 8 April 2020 / Accepted 15 March 2021
Communicated by Benny K.K. Chan

The interpretation of isotopic data in ecology requires knowledge about two factors - turnover rate and the trophic discrimination factor - which have not been well described in freshwater shrimps. We performed a 142-day diet shift experiment on 174 individuals of the omnivore shrimp, Macrobrachium borellii, measured their growth, and temporally serially sampled muscle and hepatopancreas tissue to quantify carbon and nitrogen incorporation rates and isotope discrimination factors. Shrimps were fed with artificial diets (δ13C = -26.1‰, δ15N= 2.1‰) for 45 days attempts to standardize the shrimps’ initial δ13C and δ15N values for subsequent experiments. Shrimps were then feed with another artificial diet (δ13C= -16.1‰, δ15N= 15.8‰) and the change in δ13C and δ15N was observed in a period of 97 days. The trophic discrimination factor (∆) for δ13C was significantly higher in hepatopancreas (0.7 ± 0.36‰) than in muscle (-0.1 ± 0.83‰); however, the opposite was the case for δ15N (1.7 ± 0.43‰ and 3.6 ± 0.42‰, respectively). In the hepatopancreas the mean residence time (τ) of 13C was 26.3 ± 4.3 days compared to a residence time of 16.6 ± 5.51 days for δ15N, whereas the τ in muscle was 75.8 ± 25 days for δ13C and 40 ± 25 days for δ15N. The rate of incorporation of carbon into muscle was higher than that predicted by allometric equations relating isotopic incorporation rate to body mass that was developed previously for invertebrates. Our results support ranges of traditional trophic discrimination factor values observed in muscles samples of different taxa (Δ15N around 3‒3.5‰ and Δ13C around 0‒1‰), but our work provides evidence that these traditionally used values may vary in other tissues, as we found that in the hepatopancreas Δ15N is around 1.7‰.

Key words: Stable isotopes, Carbon, Nitrogen, Muscle, Hepatopancreas.

Citation: Viozzi MF, Martínez del Rio C, Williner V. 2021. Tissue-specific isotopic incorporation turnover rates and trophic discrimination factors in the freshwater shrimp Macrobrachium borellii (Crustacea: Decapoda: Palaemonidae). Zool Stud 60:0bb. doi:-.