TY  - JOUR
A1  - Lukas, Marcus
A1  - Wacker, Alexander
T1  - Daphnia's dilemma: adjustment of carbon budgets in the face of food and  cholesterol limitation
JF  - The journal of experimental biology
N2  - We studied the carbon (C) metabolism in Daphnia when the amount of C (food quantity) and/or the content of biochemical nutrients (food quality) was limiting. Growth performances and C budgets of Daphnia magna (assimilation, faeces egestion, excretion and respiration measured by [C-14]-tracing) were analysed when animals were raised on different food quantities and concentrations of cholesterol, an essential biochemical food compound. Cholesterol is of special interest because it not only acts as limiting nutrient but also contributes to the overall C pool of the animals. As the tissue cholesterol concentration in Daphnia is quite low, we hypothesized the selective exclusion of cholesterol from C budgeting and tested this using radiolabelled cholesterol. Somatic growth rates of D. magna were highest at high quantity and quality and were reduced to a moderate value if either the food quantity or the cholesterol concentration was low. Growth was lowest at low food quantity and quality. The measurements of C budgets revealed high regulative response to low food quality at high food quantity only. Here, low dietary cholesterol caused bulk C assimilation efficiency (AE) to decrease and assimilated (excess) C to be increasingly respired. Additionally, Daphnia enhanced efficient adjustment of C budgets when facing cholesterol limitation by (1) increasing the AE of the cholesterol itself and (2) not changing cholesterol respiration, which was still not detectable. In contrast, at low food quantity, Daphnia is unable to adjust for low food quality, emphasizing that food limitation could overrule food quality effects.
KW  - Biochemical limitation
KW  - Carbon budgets
KW  - Zooplankton
KW  - Carbon pathway
KW  - Food quality
KW  - Food quantity
Y1  - 2014
U6  - https://doi.org/10.1242/jeb.094151
SN  - 0022-0949
SN  - 1477-9145
VL  - 217
IS  - 7
SP  - 1079
EP  - 1086
PB  - Company of Biologists Limited
CY  - Cambridge
ER  -