Limits...
Juvenile food limitation in standardized tests: a warning to ecotoxicologists.

Zimmer EI, Jager T, Ducrot V, Lagadic L, Kooijman SA - Ecotoxicology (2012)

Bottom Line: In a simulation study with the DEB model, we compared the effects of three hypothetical toxicants in different feeding situations.The initial food limitation when fed with lettuce always intensified the effect of the toxicants.When fed with fish flakes, the predicted effect of the toxicants was less pronounced.

View Article: PubMed Central - PubMed

Affiliation: Department of Theoretical Biology, Faculty of Earth & Life Sciences, Vrije Universiteit, de Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands. elke.zimmer@vu.nl

ABSTRACT
Standard ecotoxicological tests are as simple as possible and food sources are mainly chosen for practical reasons. Since some organisms change their food preferences during the life-cycle, they might be food limited at some stage if we do not account for such a switch. As organisms tend to respond more sensitively to toxicant exposure under food limitation, the interpretation of test results may then be biased. Using a reformulation of the von Bertalanffy model to analyze growth data of the pond snail Lymnaea stagnalis, we detected food limitation in the early juvenile phase. The snails were held under conditions proposed for a standardized test protocol, which prescribes lettuce as food source. Additional experiments showed that juveniles grow considerably faster when fed with fish flakes. The model is based on Dynamic Energy Budget (DEB) theory, which allows for mechanistic interpretation of toxic effects in terms of changes in energy allocation. In a simulation study with the DEB model, we compared the effects of three hypothetical toxicants in different feeding situations. The initial food limitation when fed with lettuce always intensified the effect of the toxicants. When fed with fish flakes, the predicted effect of the toxicants was less pronounced. From this study, we conclude that (i) the proposed test conditions for L. stagnalis are not optimal, and require further investigation, (ii) fish flakes are a better food source for juvenile pond snails than lettuce, (iii) analyzing data with a mechanistic modeling approach such as DEB allows identifying deviations from constant conditions, (iv) being unaware of food limitation in the laboratory can lead to an overestimation of toxicity in ecotoxicological tests.

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Growth of the juvenile pond snails in the full life-cycle experiment (FLE) and juvenile feeding experiment (JFE), and the corresponding model predictions (left panel). JFE:  maximum level fish flakes, ▵ medium level fish flakes,  minimum level fish flakes,  ad libitum lettuce; FLE:  ad libitum lettuce. The scaled functional response f (as a proxy for food availability), resulting from the linear food limitation function (Eq. 3, Table 1) is presented as a function of time (right panel). The symbols on the model lines stand for the same regimes as in the left panel, but do not represent data points
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Fig2: Growth of the juvenile pond snails in the full life-cycle experiment (FLE) and juvenile feeding experiment (JFE), and the corresponding model predictions (left panel). JFE: maximum level fish flakes, ▵ medium level fish flakes, minimum level fish flakes, ad libitum lettuce; FLE: ad libitum lettuce. The scaled functional response f (as a proxy for food availability), resulting from the linear food limitation function (Eq. 3, Table 1) is presented as a function of time (right panel). The symbols on the model lines stand for the same regimes as in the left panel, but do not represent data points

Mentions: The growth curves of the JFE are shown in Fig. 2 (left panel). The newborn pond snails grow much faster when fed with fish flakes, and reach double the size of the lettuce-fed snails after four weeks. Note that we used the mean growth of regime Lettuce 1 and 2, since they were not significantly different (see Online Resource, Table 5). Additionally, there is a difference between the juveniles fed with lettuce in the JFE compared to the juveniles in the FLE: the juveniles in the FLE only reached half the size of the juveniles in the JFE after four weeks, which is reflected in the difference between alet1 and alet2. The estimated food quality factors a as well as the constant scaled functional responses f0 for each regime are listed in Table 1. The scaled functional responses resulting from Eq. 3 over time are presented in Fig. 2 (right panel). Note that f(L) is still between 0 and 1 by definition.


Juvenile food limitation in standardized tests: a warning to ecotoxicologists.

Zimmer EI, Jager T, Ducrot V, Lagadic L, Kooijman SA - Ecotoxicology (2012)

Growth of the juvenile pond snails in the full life-cycle experiment (FLE) and juvenile feeding experiment (JFE), and the corresponding model predictions (left panel). JFE:  maximum level fish flakes, ▵ medium level fish flakes,  minimum level fish flakes,  ad libitum lettuce; FLE:  ad libitum lettuce. The scaled functional response f (as a proxy for food availability), resulting from the linear food limitation function (Eq. 3, Table 1) is presented as a function of time (right panel). The symbols on the model lines stand for the same regimes as in the left panel, but do not represent data points
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3475972&req=5

Fig2: Growth of the juvenile pond snails in the full life-cycle experiment (FLE) and juvenile feeding experiment (JFE), and the corresponding model predictions (left panel). JFE: maximum level fish flakes, ▵ medium level fish flakes, minimum level fish flakes, ad libitum lettuce; FLE: ad libitum lettuce. The scaled functional response f (as a proxy for food availability), resulting from the linear food limitation function (Eq. 3, Table 1) is presented as a function of time (right panel). The symbols on the model lines stand for the same regimes as in the left panel, but do not represent data points
Mentions: The growth curves of the JFE are shown in Fig. 2 (left panel). The newborn pond snails grow much faster when fed with fish flakes, and reach double the size of the lettuce-fed snails after four weeks. Note that we used the mean growth of regime Lettuce 1 and 2, since they were not significantly different (see Online Resource, Table 5). Additionally, there is a difference between the juveniles fed with lettuce in the JFE compared to the juveniles in the FLE: the juveniles in the FLE only reached half the size of the juveniles in the JFE after four weeks, which is reflected in the difference between alet1 and alet2. The estimated food quality factors a as well as the constant scaled functional responses f0 for each regime are listed in Table 1. The scaled functional responses resulting from Eq. 3 over time are presented in Fig. 2 (right panel). Note that f(L) is still between 0 and 1 by definition.

Bottom Line: In a simulation study with the DEB model, we compared the effects of three hypothetical toxicants in different feeding situations.The initial food limitation when fed with lettuce always intensified the effect of the toxicants.When fed with fish flakes, the predicted effect of the toxicants was less pronounced.

View Article: PubMed Central - PubMed

Affiliation: Department of Theoretical Biology, Faculty of Earth & Life Sciences, Vrije Universiteit, de Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands. elke.zimmer@vu.nl

ABSTRACT
Standard ecotoxicological tests are as simple as possible and food sources are mainly chosen for practical reasons. Since some organisms change their food preferences during the life-cycle, they might be food limited at some stage if we do not account for such a switch. As organisms tend to respond more sensitively to toxicant exposure under food limitation, the interpretation of test results may then be biased. Using a reformulation of the von Bertalanffy model to analyze growth data of the pond snail Lymnaea stagnalis, we detected food limitation in the early juvenile phase. The snails were held under conditions proposed for a standardized test protocol, which prescribes lettuce as food source. Additional experiments showed that juveniles grow considerably faster when fed with fish flakes. The model is based on Dynamic Energy Budget (DEB) theory, which allows for mechanistic interpretation of toxic effects in terms of changes in energy allocation. In a simulation study with the DEB model, we compared the effects of three hypothetical toxicants in different feeding situations. The initial food limitation when fed with lettuce always intensified the effect of the toxicants. When fed with fish flakes, the predicted effect of the toxicants was less pronounced. From this study, we conclude that (i) the proposed test conditions for L. stagnalis are not optimal, and require further investigation, (ii) fish flakes are a better food source for juvenile pond snails than lettuce, (iii) analyzing data with a mechanistic modeling approach such as DEB allows identifying deviations from constant conditions, (iv) being unaware of food limitation in the laboratory can lead to an overestimation of toxicity in ecotoxicological tests.

Show MeSH
Related in: MedlinePlus