Trophic discrimination factor of nitrogen isotopes within amino acids in the dobsonflyProtohermes grandis(Megaloptera: Corydalidae) larvae in a controlled feeding experiment.
The trophic discrimination factor (TDF) of nitrogen isotopes (15N/14N) within amino acids, between a stream-dwelling dobsonfly larva (Protohermes grandis: Megaloptera; Corydalidae) and its diet (chironomid larvae), was determined in controlled feeding experiments. Last-instar larvae ofP. grandiswere collected from the Yozawa-gawa River, central Japan, and reared in the laboratory. After fed to satiation for 1 month, one group of larvae was each fed one living chironomid larva per day for 4 weeks, while a second group was starved for 8 weeks. The larvae were harvested at intervals and the nitrogen isotopic composition of glutamic acid (δ15NGlu) and phenylalanine (δ15NPhe) were determined to calculate TDF. The mean TDF of satiated and starved larvae were 7.1‰ ± 0.5‰ (n= 3) and 7.3‰ ± 0.5‰ (n=5), respectively. Thus, the TDF forP. grandislarvae in this study was similar to that reported for other arthropods (approximately 7‰) and was independent of satiation or starvation. A previous study of wildP. grandislarvae, based on theδ15NGluandδ15NPhevalues, estimated its trophic position (TP) as approximately 2.0 ± 0.1 (n=5), a low value close to that of algivores, although they are generally characterized as carnivores (usually accepted as TP ≥ 3). The TDF forP. grandislarvae suggests that their low TPs in nature were caused by incorporation of vascular plant-derived amino acids (with a differentδ15N profile from that of algae) and not by an unusually low TDF or by the effects of the satiation/starvation on amino acid metabolism.
Japan Agency for Marine-Earth Science and Technology Yokosuka Kanagawa Japan; Present address: ETH Zürich Sonneggstrasse 58092 Zürich Switzerland.
Naoto F
0000-0002-8268-9512
NF
Ishikawa
Department of Biology Tokyo Metropolitan University Hachioji Tokyo Japan.
Fumio
F
Hayashi
Japan Agency for Marine-Earth Science and Technology Yokosuka Kanagawa Japan.
Yoko
Y
Sasaki
Japan Agency for Marine-Earth Science and Technology Yokosuka Kanagawa Japan; Present address: Institute of Low Temperature Science Hokkaido University Kita 19, Nishi 8, Kita-ku Sapporo 060-0819 Japan.
Yoshito
Y
Chikaraishi
Japan Agency for Marine-Earth Science and Technology Yokosuka Kanagawa Japan.
Naohiko
N
Ohkouchi
compound‐specific isotope analysis of amino acids; deamination; starvation; top predator; trophic position