The role of polyunsaturated fatty acids for the competition in herbivorous zooplankton
Final Report Abstract
A major factor determining the trophic transfer efficiency in lakes and ponds is the food quality of algae and cyanobacteria for Daphnia. Several correlative studies point at an in-situ limitation of Daphnia by a low content of the polyunsaturated fatty acid (PUFA) eicosapentaenoic acid (EPA, C20:5 n-3) in natural phytoplankton, and numerous experimental studies have demonstrated negative effects of EPA-limitation on somatic growth and reproduction of Daphnia. These negative effects of EPA-limitation were stronger at lower temperatures than at 20°C. This proposal aimed at investigating, if the limiting resource EPA may affect the competition among Daphnia and how an EPA-limitation would affect the clonal composition of a Daphnia community. In order to consider ecologically relevant scenarios, we focused on co-existing Daphnia genotypes that have a common ecological and evolutionary history and, as proposed, we did not confine our research to D. magna but as well included D. longispina. It was proposed to investigate, if the EPA-demand differs (i) between clones of the same species and (ii) how this would affect competition/co-existence between Daphnia clones. To achieve this, we ran mesocosm experiments with D. longispina genotypes originating from a single lake on natural phytoplankton from the same lake, which provided a gradient of food with different fatty acid profiles. Correlations strongly suggest that different Daphnia genotypes were limited by different single PUFAs. Upon growth at 20°C and 15°C, co-existing D. magna genotypes showed changes in their fatty acid composition. Although the patterns of changes in fatty acid composition differed, the genotypes achieved similar membrane fluidity and growth performance and hence showed phenotypic convergence. This result independently corroborates the finding of an unexpectedly high diversity within Daphnia populations with respect to which particular fatty acids are changed in response to temperature changes. In addition to these correlative studies, highly controlled life-history experiments using food with increasing supplementation of EPA via liposomes were performed at 15°C with single co-existing D. magna genotypes. Thorough statistical analyses based on modified Bertalanffy saturation curves clearly revealed that reaction norms of Daphnia genotypes were crossing with changing EPA- content of the food. These findings strongly suggest that differences in EPA-content of the food can change the order of the Daphnia genotypes if they are arranged according to decreasing growth rates, i.e. there is strong evidence that differences in EPA-content in phytoplankton will affect competition among co-existing Daphnia genotypes. In conclusion, for the first time the effects of dietary PUFAs and EPAs on Daphnia have been addressed on the level of populations and have revealed variable ‘strategies’ of Daphnia genotypes of how to change their fatty acid profiles in response to temperature changes. This implies that co-existing Daphnia genotypes may be under limitation by different PUFAs when consuming the same phytoplankton.
Publications
- 2018. Global warming: testing for direct and indirect effects of temperature at the interface of primary producers and herbivores. Frontiers of Ecology and Evolution 6, 87
von Elert, E., Fink, P.
(See online at https://doi.org/10.3389/fevo.2018.00087) - 2019. Differences in heat tolerance within a Daphnia magna population: the significance of body PUFA content. Hydrobiologia 846, 17–26
Werner, C., Ilić, M., von Elert, E.
(See online at https://doi.org/10.1007/s10750-018-3769-7) - 2021. Phenotypic convergence in a natural Daphnia population acclimated to low temperature. Ecol Evol 11, 15312–15324
Werner, C., Otte, K.A., von Elert, E.
(See online at https://doi.org/10.1002/ece3.8217)
