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- Title
Trophic discrimination factor of nitrogen isotopes within amino acids in the dobsonfly Protohermes grandis (Megaloptera: Corydalidae) larvae in a controlled feeding experiment.
- Authors
Ishikawa, Naoto F.; Hayashi, Fumio; Sasaki, Yoko; Chikaraishi, Yoshito; Ohkouchi, Naohiko
- Abstract
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 of P. grandis were 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 for P. grandis larvae in this study was similar to that reported for other arthropods (approximately 7‰) and was independent of satiation or starvation. A previous study of wild P. grandis larvae, based on the δ15NGlu and δ15NPhe values, 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 for P. grandis larvae suggests that their low TPs in nature were caused by incorporation of vascular plant-derived amino acids (with a different δ15N profile from that of algae) and not by an unusually low TDF or by the effects of the satiation/starvation on amino acid metabolism.
- Subjects
NITROGEN isotopes; AMINO acids; MEGALOPTERA; CORYDALIDAE; DEAMINATION; LARVAE
- Publication
Ecology & Evolution (20457758), 2017, Vol 7, Issue 6, p1674
- ISSN
2045-7758
- Publication type
Article
- DOI
10.1002/ece3.2728