TY  - JOUR
A1  - Lukas, Marcus
A1  - Wacker, Alexander
T1  - Acclimation to dietary shifts impacts the carbon budgets of Daphnia magna
JF  - Journal of plankton research
N2  - Daphnia responds to low availability of carbon (food quantity) or limiting concentrations of nutrients relative to carbon (C) in excess (food quality) by respectively saving or discharging C via different pathways. We investigated which kind of food limitation leads to a faster regulation in Daphnia C budgets, and whether the pre-assimilative C pathways, ingestion and faeces egestion and the post-assimilative C pathways, excretion and respiration, are regulated concurrently. Daphnia magna were exposed to dietary shifts in different food quantities or qualities; food quality was varied in terms of the essential component, cholesterol. After acclimation to the new diet ranging from 0 to 96 h, C budgets were measured by a radiotracer technique. Dietary shifts in quantity and quality caused Daphnia to quickly adjust their C budgets within 6 h, but different C pathways were affected. A shift to low food quantity reduced Daphnia respiration indicating C retention. In contrast, sudden low quality food caused increased faeces egestion to discharge excess C. Furthermore, we observed a delayed increase in excretion but no change in respiration within the time frame studied. Such time-shifted responses appear to be an appropriate means to keep the costs of physiological adjustments relatively low, which in turn would benefit Daphnia performance.
KW  - carbon pathway
KW  - cholesterol
KW  - zooplankton
KW  - food quality
KW  - food quantity
Y1  - 2014
U6  - https://doi.org/10.1093/plankt/fbu018
SN  - 0142-7873
SN  - 1464-3774
VL  - 36
IS  - 3
SP  - 848
EP  - 858
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Lukas, Marcus
A1  - Wacker, Alexander
T1  - Constraints by oxygen and food quality on carbon pathway regulation: a co-limitation study with an aquatic key herbivore
JF  - Ecology : a publication of the Ecological Society of America
N2  - In food webs, herbivores are often constrained by low food quality in terms of mineral and biochemical limitations, which in aquatic ecosystems can co-occur with limited oxygen conditions. As low food quality implies that carbon (C) is available in excess, and therefore a regulation to get rid of excess C is crucial for the performance of consumers, we examined the C pathways (ingestion, feces release, excretion, and respiration) of a planktonic key herbivore (Daphnia magna). We tested whether consumer C pathways increase due to mineral (phosphorus, P) or biochemical (cholesterol and fatty acid) limitations and how these regulations vary when in addition oxygen is low. Under such conditions, at least the capability of the upregulation of respiration may be restricted. Furthermore, we discussed the potential role of the oxygen-transporting protein hemoglobin (Hb) in the regulation of C budgets. Different food quality constraints led to certain C regulation patterns to increase the removal of excess dietary C: P-limited D. magna increased excretion and respiration, while cholesterol-limited Daphnia in addition upregulated the release of feces. In contrast, the regulative effort was low and only feces release increased when D. magna was limited by a long-chain polyunsaturated fatty acid (eicosapentaenoic acid, EPA). Co-limiting oxygen did not always impact the discharge of excess C. We found the food-quality-induced upregulation of respiration was still present at low oxygen. In contrast, higher excretion of excess C was diminished at low oxygen supply. Besides the effect that the Hb concentration increased under low oxygen, our results indicate a low food-quality-induced increase in the Hb content of the animals. Overall, C budgeting is phenotypically plastic towards different (co-) limiting scenarios. These trigger specific regulation responses that could be the result of evolutionary adaptations.
KW  - carbon budget
KW  - carbon stoichiometry
KW  - cholesterol
KW  - co-limitation
KW  - Daphnia
KW  - EPA
KW  - hemoglobin
KW  - oxygen
KW  - phosphorus
KW  - polyunsaturated fatty acid
KW  - zooplankton
Y1  - 2014
SN  - 0012-9658
SN  - 1939-9170
VL  - 95
IS  - 11
SP  - 3068
EP  - 3079
PB  - Wiley
CY  - Washington
ER  -