Mrs E. (Elke) Zimmer

Room: T544
Phone: +31-(0)20-5987246
Email: elke.zimmer@falw.vu.nl
Curriculum vitae: 1984 born in Norden, East Friesland, Germany
2004 Abitur, Norden
2009 Diplom Marine Environmental Science, Oldenburg
Diploma thesis "Analyzing endocytosis by generalized modeling", MPIPKS Dresden
Specialization: Marine and environmental sciences
Project: Modelling effects of toxicants
Courses:
DEB tele course
Publications:

Background

In this project, I will quantitatively investigate how changes in the embryonic life-history traits due to toxic stress influence the dynamics of a population.

Standard toxicity tests are made with juveniles or adults, and the impact of toxicants on the embryonic life-history traits has hardly been studied. But the embryonic development is closely related to the rest of the life-cycle, and is often considered as to be very sensitive to environmental conditions. Dynamic Energy Budget (DEB) theory provides a set of rules that describes the whole life-cycle of an organism and is therefore an excellent choice for this kind of investigation. I will use DEB theory to describe and understand the effect of toxicants on the different life-history traits of the pond snail Lymnaea stagnalis, which is the test organism in my partner project DEB-2, and investigate the propagation of the effects to the population level.

Overall aim of the project:

The outcome of this project will provide a better understanding of the relevance of toxicant effects on the embryonic development for the dynamics of a population.

Specific hypotheses / questions

How do effects of toxicants on different metabolic processes influence the embryonic development?

Embryogenesis is often considered to be the most sensitive stage of an organism, and at the same time of central importance for the maintenance of a population. I will investigate the effect of toxicants on different metabolic processes, and the influence of this effects on the embryonic life-history traits (hatching time, hatchling size, egg size...), mainly based on data from the literature and model simulations using DEB.

How does toxic stress during embryogenesis affect the population?

Due to the variety of toxicants in the environment, each metabolic process of an organism can be affected by toxicants, and each life-history trait can be changed. I will investigate the importance of the different embryonic traits for the population level. I will additionally investigate the impact of stress during embryogenesis in relation to stress in other stages during life-cycle for the population dynamics.

How does reproduction change due to different feeding conditions or stress?

A standard assumption in DEB theory is that a mother produces offspring with the same reserve density at birth that she has at the moment off egg laying. In other words, mothers under non-limiting conditions should produce larger eggs than mothers under poor feeding conditions or even starvation. But under certain conditions, some species (e.g. Daphnia magna) seem to produce large but less eggs under poor conditions, and many but smaller eggs under good conditions. I will investigate the reproductive investment of Lymnaea stagnalis and the embryonic life-history traits of the offspring under varying food conditions and under toxic stress in cooperation with the DEB-2 project.

Lettuce is not the optimal food source for juveniles.

It has been observed that the juvenile pond snails grow slower than expected from DEB under apparently non-limiting food conditions in the lab. One food source that is often used for experiments with L. stagnalis is lettuce, which might not be optimal food for pond snails. However, in the adult stage, the snails seem to grow normal (at least they follow the DEB predictions). We hypothesize that lettuce is not an optimal food source for juveniles, and that the juveniles in the experiments are stressed due to limited food despite a large amount of lettuce available. If juvenile snails are already stressed due to the wrong food, toxic effects may be difficult to interpret due to possible interaction with food limitation.

Male and female reproductive output: how to include both buffers in DEB?

The hermaphroditic pond snail L. stagnalis reproduces both as male and as female, but does not self-fertilize if it has the possibility to mate. The choice of its sex in a mating event depends on many different factors, which will not be focus of this project. But experimental work indicates that male reproductive output is a substantial part of the budget allocated to reproduction. Therefore, it is of importance to include both buffers in the Dynamic Energy Budget model.

Approach to be used

Modeling: Proposed experiments:

Expected significance of the results

The outcome of the project will give new insights into the importance of toxic effects on the embryogenesis for the population level. Until now, standard toxicity tests are made with juveniles and/or adults. It is often assumed that an organism is much more sensitive during the embryonic development, and it is possible that even very small concentrations of toxicants exposed to embryos can have a large effect on the population. In this project, I will quantitatively investigate how changes in the embryonic life-history traits due to toxic stress influence the dynamics of a population. DEB has proven to be a very strong tool for ecotoxicological investigations, and the combination with an Individual Based Model will provide excellent insight into the impacts of toxicants on populations and thereby improve risk assessment.

Relation to other CREAM projects

My project is related to the DEB-2 project, which is my partner project. In DEB-2, the effects of reprotoxic substances on Lymnaea stagnalis will be investigated, amongst others with a life-cycle test, and be will analyzed with DEB.

My project is also related to the projects Scales-1 (also individual and population), Scales-2 (TK/TD modeling, sub-lethal effects), and Daphnia-2 (also uses DEB).

Publication plan for the project

DEB-IBM (co-authorship)

In this article, an implementation of the standard DEB equations in an IBM framework of NetLogo will be published. The first steps of the implementation were done at the CREAM course "Ecological modeling" in corporation with Ben Martin (Daphnia-2). The main goal is to provide an user friendly implementation of the basic DEB individual in a population; the manuscript is about to be submitted.\\ Submission to Methods in Ecology and Evolution: January 2011

Juvenile food limitation: be warned, ecotoxicologists!

Food limitation in juveniles can lead to an overestimation of toxic effects on the population level. Juvenile organisms grow fast and therefore need food with high protein content.

In many standardized experimental setups, the test organisms are food limited during the juvenile phase due to insufficient protein content of the given food.

With simulations, I will show that experiments with food limited juveniles can lead to an overestimation of toxic effects on the population level.

Submission to Ecotoxicology: April 2011

Reproductive investment

A standard assumption in DEB theory is that a mother produces offspring with the same reserve density that she has at the moment off egg laying. But under certain conditions, some species (e.g. Daphnia magna) seem to produce large but less eggs under poor conditions, and many but smaller eggs under good conditions. To validate the DEB predictions (or propose changes to the theory), I will do experiments with adults at different food levels. The focus will be put on the embryonic life-history traits such as number and size of eggs, hatching time and success and hatchling size. The results and their relevance for DEB theory will be discussed in the publication.

Submission to Functional Ecology: October 2011

Theoretical analysis of the effect of toxicants on embryonic life-history traits and the effect on the population dynamics

Using simulations, I will show what can happen to the life-history of the pond snail when different metabolic parameters are changed due to toxic stress. Assuming that the metabolic processes in the embryo have the same sensitivity as in the other life stages, I will explicitly include the embryonic stage in the model to analyze how the embryonic life-history traits can be altered due to toxicants. I will investigate the propagation to the population level using an IBM, coded in C++, and discuss the ecological relevance of the outcome.

Submission: Summer 2012

Co-publications with Alpar(DEB-2)

Due to the cooperation with the DEB-2 project (and possibly also with others CREAM fellows), I expect to co-publish other publications which are not yet planned (as for example also the DEB-IBM publication).
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