TY - JOUR A1 - Lukas, Marcus A1 - Frost, Paul C. A1 - Wacker, Alexander T1 - The neonate nutrition hypothesis - early feeding affects the body stoichiometry of Daphnia offspring JF - Freshwater biology N2 - Aquatic herbivores consume variable quantities and qualities of food. In freshwater systems, where phosphorus (P) is often a primary limiting element, inadequate dietary P can slow maternal growth and reduce body P content. There remains uncertainty about whether and how dietary effects on mothers are transferred to offspring by way of egg provisioning. Using the keystone herbivore Daphnia, we tested a novel explanation (the neonate nutrition hypothesis') to determine whether the early nutrition of newborns affects their elemental composition and whether the indications of differences in maternal P nutrition found previously might be overestimated. We thus examined the P content of mothers and their eggs from deposition through development to the birth of neonates. We examined further whether very short periods of ingestion (3h) by the offspring alter the overall P content of juvenile Daphnia. We showed that strong dietary P effects on mothers were not directly transferred to their eggs. Irrespective of the supply of P in the maternal diet, the P content of eggs in different developmental stages and in (unfed) neonates did not differ. This indicates that Daphnia mothers do not reduce the quality (in terms of P) of newly produced offspring after intermittent periods (i.e. several days) of poor nutrition. In contrast, the P content of neonates reflected that of their food after brief periods of feeding, indicating that even temporary exposure to nutrient poor food immediately after birth may strongly affect the elemental composition of neonates. Our results thus support the neonate nutrition hypothesis, which, like differential maternal provisioning, is a possible explanation for the variable elemental quality of young Daphnia. KW - ecological stoichiometry KW - food quality KW - maternal effects KW - nutrient limitation KW - zooplankton Y1 - 2013 U6 - https://doi.org/10.1111/fwb.12213 SN - 0046-5070 VL - 58 IS - 11 SP - 2333 EP - 2344 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Lukas, Marcus A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Growth Rate Hypothesis does not apply across colimiting conditions cholesterol limitation affects phosphorus homoeostasis of an aquatic herbivore JF - Functional ecology : an official journal of the British Ecological Society N2 - 1. Herbivores show stronger control of element homoeostasis than primary producers, which can lead to constraints in carbon and nutrient transfer efficiencies from plants to animals. Insufficient dietary phosphorus (P) availability can cause reduced body P contents along with lower growth rates of animals, leading to a positive relationship between growth and body P. 2. We examined how a second limiting food component in combination with dietary P limitation influences growth and P homoeostasis of a herbivore and how this colimitation influences the hypothesized positive correlation between body P content and growth rates. Therefore, we investigated the responses in somatic growth and P stoichiometry of Daphnia magna raised on a range of diets with different amounts of P and the sterol cholesterol. 3. Somatic growth rates of D. magna increased asymptotically with increasing P as well as with increasing cholesterol availability. The body P content increased with increasing dietary P and stabilized at high dietary P availability. The observed plasticity in D. magna's P stoichiometry became stronger with increasing cholesterol availability, i.e. with decreasing colimitation by cholesterol. 4. At P-limiting conditions, the positive correlation between body P content and growth rate, as predicted by the growth rate hypothesis (GRH) applied to the within-species level, declined with increasing cholesterol limitation and disappeared entirely when cholesterol was not supplied. Thus, even when Daphnia shows no growth response owing to strong limitation by the colimiting nutrient, the body P content may vary substantially, calling into question the unconditional use of herbivores' P content as predictor of a potential P limitation in nature. 5. The observed interaction between dietary P and cholesterol on Daphnia's growth and stoichiometry can be used as a conceptual framework of how colimiting essential nutrients affect herbivore homoeostasis, and provide further insights into the applicability of the GRH within a consumer species. KW - colimitation KW - Daphnia KW - ecological stoichiometry KW - essential resources KW - food quality KW - imbalanced diet KW - nutrient limitation KW - nutritional ecology KW - zooplankton Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2435.2011.01876.x SN - 0269-8463 VL - 25 IS - 6 SP - 1206 EP - 1214 PB - Wiley-Blackwell CY - Malden 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 - 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 - 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 - Spijkerman, Elly A1 - Lukas, Marcus A1 - Wacker, Alexander T1 - Ecophysiological strategies for growth under varying light and organic carbon supply in two species of green microalgae differing in their motility JF - Phytochemistry : an international journal of plant biochemistry N2 - Mixing events in stratified lakes result in microalgae being exposed to varying conditions in light and organic carbon concentrations. Stratified lakes consist of an upper illuminated strata and a lower, darker strata where organic carbon accumulates. Therefore, in this contribution we explore the importance of dissolved organic carbon for growth under various light intensities by measuring some ecophysiological adaptations in two green microalgae. We compared the non-motile Chlorella vulgaris with the flagellated Chlamydomonas acidophila under auto-, mixo-, and heterotrophic growth conditions. In both algae the maximum photosynthetic and growth rates were highest under mixotrophy, and both algae appeared inhibited in their phosphorus acquisition under heterotrophy. Heterotrophic conditions provoked the largest differences as C. vulgaris produced chlorophyll a in darkness and grew as well as in autotrophic conditions, whereas Chl. acidophila bleached and could not grow heterotrophically. Although the fatty acid composition of both phytoplankton species differed, both species reacted in a similar way to changes in their growth conditions, mainly by a decrease of C18:3n-3 and an increase of C18:1n-9 from auto- to heterotrophic conditions. The two contrasting responses within the group of green microalgae suggest that dissolved organic carbon has a high deterministic potential to explain the survival and behaviour of green algae in the deeper strata of lakes. KW - Chlamydomonas acidophila KW - Chlorella vulgaris KW - Chlorophyceae KW - Ecophysiology on freshwater phytoplankton KW - Glucose KW - Mixotrophy KW - Osmotrophy KW - Heterotrophy KW - Photosynthesis KW - Fatty acids Y1 - 2017 U6 - https://doi.org/10.1016/j.phytochem.2017.08.018 SN - 0031-9422 SN - 1873-3700 VL - 144 SP - 43 EP - 51 PB - Elsevier CY - Oxford ER -