Main supervisor: Yngvild Vindenes
Co-supervisors: ?ystein Langangen and Jan David Heuschele
Note: This is the second of two proposed projects based on video analyses of trait responses in Daphnia magna. Data for two treatments are shared with the other project, and methods for video analysis may be developed in collaboration between the students.
Background
Global climate change is not only increasing the long-term average temperature, but in many locations also the magnitude of short-term fluctuations on a daily or seasonal scale. Understanding how organisms are adapted to fluctuating temperature is therefore important for predicting how they might respond to global warming. Since the temperature responses of ectotherms (such as the metabolic rate or population growth rate) are highly non-linear (see figure 1), we can expect that their responses to fluctuating temperature will largely depend on whether they live in an average cold or warm environment (Ruel and Ayres 1999, Lawson et al. 2015). While some studies have investigated such responses for fitness and directly fitness-related traits, there is currently a lack of studies of how morphological and behavioral traits respond to fluctuating temperatures through life, or how much they differ between different genotypes. Repeated video measurements, available from previous work, provide a unique opportunity to obtain such data.
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Study organism
The water flea Daphnia magna is a model organism for a range of questions in ecology and evolutionary biology. It has a wide distribution in freshwaters and brackish waters around the world, and is commonly found in small water bodies (rockpools, ponds). Its life history shows several adaptations to a highly variable and unpredictable environment, including resting stages that can remain dormant for decades and an altering sexual and asexual part of the life cycle. In the asexual part of the life cycle, D. magna reproduces clonally, which makes this organism ideal for experiments to separate out effects of environment and genotype.
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Photo (Y. Vindenes): A Daphnia magna female with eggs in the brood pouch (on the back). |
Project description
We have available videos from a long-term experiment with the water flea Daphnia magna (see Vindenes et al 2025 for details on the experimental setup), providing a unique opportunity to study trait responses to temperature fluctuations in four different clonal lines (genotypes) originating from different locations (Morocco, Italy, and Sweden). The study included 160 individuals at two constant and two fluctuating temperatures (10±5°C and 25±5°C). In the fluctuating treatments, the temperature was changed every 12 hours (coldest during night) to obtain a 24 hour cycle. Each individual was filmed multiple times (for 30 seconds each time) throughout its life from birth to death, providing a large set of videos which can be analysed with modern techniques for image analysis to measure various traits and how they change through life. So far, we have analysed the videos to obtain estimates of body length at different ages at constant temperatures (Broch and Heuschele 2023, Vindenes et al. 2025), but not yet for other morphological measures (such as spine length), or swimming behaviour (such as swimming speed or rotation), or for body length in fluctuating temperatures.
The work in this master project will consist of analysing the videos based on image analysis methods (Cho et al. 2022, Broch and Heuschele 2023), to obtain a dataset of individual trait responses through life, across the two fluctuating temperatures and corresponding two constant mean control treatments. For the length data growth models can also be developed to quantify growth through life. The student will further analyse this dataset on multiple traits using statistical models to quantify differences in traits between the treatments. More detailed hypotheses and study questions will be developed by the student depending on their specific interests, in collaboration with the project team. The project is suitable for a student who is interested in ectotherm responses to global warming, who is comfortable working with programming and statistical analyses.
Sources
- Broch, C., and J. Heuschele. 2023. Zoobooth: A portable, open-source and affordable approach for repeated size measurements of live individual zooplankton. Heliyon 9:e15383.
- Cho, Y., R. A. Jonas-Closs, L. Y. Yampolsky, M. W. Kirschner, and L. Peshkin. 2022. Intelligent high-throughput intervention testing platform in Daphnia. Aging Cell 21:e13571.
- Lawson, C. R., Y. Vindenes, L. Bailey, and M. van de Pol. 2015. Environmental variation and population responses to global change. Ecology Letters 18:724–736.
- Ruel, J. J., and M. P. Ayres. 1999. Jensen’s inequality predicts effects of environmental variation. Trends in Ecology & Evolution 14:361–366.
- Vindenes, Y., C. Broch, T. Andersen, D. O. Hessen, and T. Ergon. 2025. Understanding the role of ageing in the thermal responses of life history and fitness in Daphnia magna. Proceedings of the Royal Society B: Biological Sciences 292:20250430.