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| Titel |
The stable isotopic composition of Daphnia ephippia reflects changes in δ13C and δ18O values of food and water |
| VerfasserIn |
J. Schilder, C. Tellenbach, M. Möst, P. Spaak, M. van Hardenbroek, M. J. Wooller, O. Heiri |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 12 ; Nr. 12, no. 12 (2015-06-23), S.3819-3830 |
| Datensatznummer |
250117996
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| Publikation (Nr.) |
 copernicus.org/bg-12-3819-2015.pdf |
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| Zusammenfassung |
| The stable isotopic composition of fossil resting eggs (ephippia) of
Daphnia spp. is being used to reconstruct past environmental conditions in lake
ecosystems. However, the underlying assumption that the stable isotopic
composition of the ephippia reflects the stable isotopic composition of the
parent Daphnia, of their diet and of the environmental water have yet to be
confirmed in a controlled experimental setting. We performed experiments
with Daphnia pulicaria cultures, which included a control treatment
conducted at 12 °C in filtered lake water and with a diet of fresh algae and
three treatments in which we manipulated the stable carbon isotopic
composition (δ13C value) of the algae, stable oxygen isotopic
composition (δ18O value) of the water and the water
temperature, respectively. The stable nitrogen isotopic composition (δ15N value) of the algae was similar for all treatments. At 12 °C, differences in algal δ13C values and in δ18O values of water were reflected in those of Daphnia. The differences
between ephippia and Daphnia stable isotope ratios were similar in the different
treatments (δ13C: +0.2 ± 0.4 ‰
(standard deviation); δ15N: −1.6 ± 0.4 ‰; δ18O: −0.9 ± 0.4 ‰), indicating that changes in dietary δ13C
values and in δ18O values of water are passed on to these
fossilizing structures. A higher water temperature (20 °C)
resulted in lower δ13C values in Daphnia and ephippia than in the
other treatments with the same food source and in a minor change in the
difference between δ13C values of ephippia and Daphnia (to −1.3 ± 0.3 ‰). This may have been due to microbial
processes or increased algal respiration rates in the experimental
containers, which may not affect Daphnia in natural environments. There was no
significant difference in the offset between δ18O and δ15N values of ephippia and Daphnia between the 12 and 20 °C
treatments, but the δ18O values of Daphnia and ephippia were
on average 1.2 ‰ lower at 20 °C than at 12 °C. We conclude that the stable isotopic composition of
Daphnia ephippia provides information on that of the parent Daphnia and of the food and
water they were exposed to, with small offsets between Daphnia and ephippia
relative to variations in Daphnia stable isotopic composition reported from
downcore studies. However, our experiments also indicate that temperature
may have a minor influence on the δ13C, δ15N and
δ18O values of Daphnia body tissue and ephippia. This aspect deserves
attention in further controlled experiments. |
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