Sekino, T., M. Nakanishi, Y. Ishida, S. Tsuge, H. Ohtani, T. Kimoto
Abstract:
Fatty acid composition of zooplankton is influenced by food composition, water temperature and their physiological status. However, analysis of fatty acid composition was limited to bulk estimate due to small mass of zooplankton. Thus, in previous zooplankton studies, intra-specific variation in fatty acid composition was not considered.
In the present study, we developed the Py-GC method and were able to analyze the fatty acid composition of a single individual zooplankter. We observed intra-specific variation of fatty acid composition in three species of crustacean zooplankton (Daphnia galeata, Diaphanosoma brachyurum and Eodiaptomus japonicus) in Lake Biwa, Japan.
Unsaturated fatty acid of C16 and C18 and saturated fatty acid from C14 to C18 were identified for each species. Comparison of fatty acid composition revealed that inter-specific difference between Daphnia and Diaphanosoma was smaller than intra-specific differences, while inter-specific differences between Eodiaptomus and the other species were greater than intra- specific variability.
C18:1 fatty acid are synthesized by unsaturation of C18:0 or by elongation of C16:1. Ratios of C18:1/C18:0 and Cl8:l/Cl6:1 of zooplankters were expected to increase when fatty acids of their food are modified by elongation (i.e. from C16:1 to Cl8:l) or unsaturation (i.e. from C18:0 to Cl8:l). The Cl8:l/Cl8:0 ratios were significantly different between Eodiaptomus and the other species (Daphnia and Diaphanosoma), but showed no significant differences between Daphnia and Diaphanosoma. However, the C18:l/Cl6:1 ratios were not significantly different among the three species. If the fatty acid composition remained constant in the zooplankton food seston, these results would imply that elongation of C16:1 showed no differences between the three species; however, Daphnia and Diaphanosoma showed differences from Eodiaptomus in unsaturation of C18:0.
The present study showed that fatty acid compositions were not significantly different among Cladocera (Daphnia and Diaphanosoma), but varied significantly between Cladocera and Copepoda (Eodiaptomus). These facts suggest that fatty acid composition of a zooplankter often reflects individual character or environmental condition rather than species character.
(Center for Ecological Research, Kyoto University, Japan)
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