How Daphnia Copes With Excess Carbon in Its Food

Oecologia. 2003 Aug;136(3):336-46. doi: 10.1007/s00442-003-1283-7. Epub 2003 Jun 19.

Abstract

Animals that maintain near homeostatic elemental ratios may get rid of excess ingested elements from their food in different ways. C regulation was studied in juveniles of Daphnia magna feeding on two Selenastrum capricornutum cultures contrasting in P content (400 and 80 C:P atomic ratios). Both cultures were labelled with (14)C in order to measure Daphnia ingestion and assimilation rates. No significant difference in ingestion rates was observed between P-low and P-rich food, whereas the net assimilation of (14)C was higher in the treatment with P-rich algae. Some Daphnia were also homogeneously labelled over 5 days on radioactive algae to estimate respiration rates and excretion rates of dissolved organic C (DOC). The respiration rate for Daphnia fed with high C:P algae (38.7% of body C day(-1)) was significantly higher than for those feeding on low C:P algae (25.3% of body C day(-1)). The DOC excretion rate was also higher when animals were fed on P-low algae (13.4% of body C day(-1)) than on P-rich algae (5.7% of body C day(-1)). When corrected for respiratory losses, total assimilation of C did not differ significantly between treatments (around 60% of body C day(-1)). Judging from these experiments, D. magna can maintain its stoichiometric balance when feeding on unbalanced diets (high C:P) primarily by disposing of excess dietary C via respiration and excretion of DOC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological*
  • Animals
  • Carbon / metabolism*
  • Daphnia / physiology*
  • Diet
  • Energy Metabolism
  • Eukaryota / chemistry
  • Homeostasis
  • Phosphorus / metabolism

Substances

  • Phosphorus
  • Carbon