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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Related in: MedlinePlus

The growth curves obtained in the full life-cycle experiment (FLE, left panel) and the partial life-cycle experiment (PLE, right panel). The symbols are the mean values of the measured shell length, the error bars the corresponding standard deviations. The lines correspond to the model predictions: the dashed line is the prediction without the juvenile food limitation function for the FLE. Right panel:  ad libitum lettuce,  50 % of ad libitum,  25 % of ad libitum
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Fig1: The growth curves obtained in the full life-cycle experiment (FLE, left panel) and the partial life-cycle experiment (PLE, right panel). The symbols are the mean values of the measured shell length, the error bars the corresponding standard deviations. The lines correspond to the model predictions: the dashed line is the prediction without the juvenile food limitation function for the FLE. Right panel: ad libitum lettuce, 50 % of ad libitum, 25 % of ad libitum

Mentions: To describe the effect of juvenile food limitation on growth, we make the scaled functional response f a function of body size. For simplicity, we use a linear function for f related to length:3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ f(L) = a f_{0} \frac{L}{L_{m}} \qquad \hbox{for} \qquad L < L_f, $$\end{document}where a is the food quality factor. This is a dimensionless constant, which relates to the quality of the provided food source. Note that we use the normalized length (L / Lm) to keep a dimensionless. The parameter f0 is the scaled functional response for L > Lf in that treatment. It will be set to one for ad libitum feeding with lettuce, and for the highest amount of fish flakes given in the juvenile feeding experiment (see description below). The growth of the snails follows the von Bertalanffy pattern after they reach a certain shell length (see Fig. 1). We call this length the critical length , and assume that above that size, the snails are not limited by food quality anymore (i.e. f = f0 in the model). Fig. 1


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

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

The growth curves obtained in the full life-cycle experiment (FLE, left panel) and the partial life-cycle experiment (PLE, right panel). The symbols are the mean values of the measured shell length, the error bars the corresponding standard deviations. The lines correspond to the model predictions: the dashed line is the prediction without the juvenile food limitation function for the FLE. Right panel:  ad libitum lettuce,  50 % of ad libitum,  25 % of ad libitum
© Copyright Policy
Related In: Results  -  Collection

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

Fig1: The growth curves obtained in the full life-cycle experiment (FLE, left panel) and the partial life-cycle experiment (PLE, right panel). The symbols are the mean values of the measured shell length, the error bars the corresponding standard deviations. The lines correspond to the model predictions: the dashed line is the prediction without the juvenile food limitation function for the FLE. Right panel: ad libitum lettuce, 50 % of ad libitum, 25 % of ad libitum
Mentions: To describe the effect of juvenile food limitation on growth, we make the scaled functional response f a function of body size. For simplicity, we use a linear function for f related to length:3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ f(L) = a f_{0} \frac{L}{L_{m}} \qquad \hbox{for} \qquad L < L_f, $$\end{document}where a is the food quality factor. This is a dimensionless constant, which relates to the quality of the provided food source. Note that we use the normalized length (L / Lm) to keep a dimensionless. The parameter f0 is the scaled functional response for L > Lf in that treatment. It will be set to one for ad libitum feeding with lettuce, and for the highest amount of fish flakes given in the juvenile feeding experiment (see description below). The growth of the snails follows the von Bertalanffy pattern after they reach a certain shell length (see Fig. 1). We call this length the critical length , and assume that above that size, the snails are not limited by food quality anymore (i.e. f = f0 in the model). Fig. 1

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