Impact of environmental change on the dynamics of freshwater zooplankton and their parasites

Zooplankton are arguably the most important trophic group in lake ecosystems. Their grazing controls algal populations, including harmful or nuisance blooms and they themselves provide food for higher trophic levels such as larger invertebrates and fish. They are instrumental for the transfer of carbon through the traditional foodweb. However, despite many years of study of zooplankton ecology we still know little about the diversity and dynamics of their parasites. Molecular ecology has revolutionised our understanding zooplankton parasite diversity, particularly in marine systems, freshwater systems are much less well characterised. Numerous organisms infect zooplankton including Bacteria, Fungi, Metazoans such as nematode worms and taxonomically diverse groups of protists. A single host may contain a reservoir of different parasite taxa as well as many epibionts but to what extent they may control zooplankton populations and competition between zooplankton species is unknown. Furthermore, with increased temperature and anthropogenic nutrient inputs we do not know how zooplankton-parasite interactions may be changing. This project will reveal the black box of parasitism in zooplankton in freshwater lakes, assessing the diversity and abundance of parasites and the impact they have on individuals and populations in response to environmental change.

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Image Captions

Monograph taken from “Die günen Armpolypen, die geschwänzten und ungeschwänzten zackigen Wasserflöhe und eine besondere Art kleiner Wasseraale” by Jacob Christian Schaffer, published in Regensburg, Germany in 1755. The picture shows Daphnia magna visible are numerous peritrich (Ciliata) epibionts attached to the dorsal surface- a common occurrence in Daphnia spp


The project will use a combination of traditional sampling techniques for zooplankton using microscopy to look at visible incidence and occurrence of known parasites as well as cutting edge molecular environmental DNA (eDNA) techniques. DNA metabarcoding and FISH (Fluorescence in-situ hybridisation) of both mixed communities and individuals will profile and identify zooplankton associated microbial parasites. Pioneering molecular work on historical (decades old) zooplankton samples preserved in formalin using novel methods developed by Dr Rowena Stern for the continuous plankton recorder (CPR) will show changes over decades in parasite diversity occurrence. Additionally molecular work pioneered at UKCEH on sediment cores will identify community profiles over longer time scales, several decades to centuries. The project will also use aquarium microcosms to model impacts of environmental change on model host-parasite systems.

Project Timeline

Year 1

In year 1 using DNA metabarcoding the project will first look at the population structure of both zooplankton host and parasites in a bi-weekly time series. It will make use of UKCEH’s Lakes monitoring program- one of the longest running freshwater time series in the world. Community profiles of both zooplankton and parasites will be obtained in modern samples, existing sediment cores and on historical preserved samples allowing the student to assess longer term potential impacts of anthropogenic change on parasite communities. Network analysis will infer some parasitic relationships on whole communities, and these will be confirmed by looking in detail at individual host taxa.

Year 2

In year 2 based on the results obtained in year 1, targeted sampling will be carried out during blooms of zooplankton and detailed investigations of parasite diversity and occurrence will be made to gain data on infection rates and community interactions, investigating how parasites control zooplankton populations. During this year the student will isolate model systems of host-parasite (or further develop and maintain existing Daphnia and Cyclops models) for use in year 3 of the project.

Year 3

In year 3 testing of model systems of host-parasite in microcosms will be conducted under varying incubations of temperature and nutrients. This will model how populations of individual hosts and parasites respond to environmental changes, addressing how the environmental factors influence infection rates and host fitness. Competition between different species will also be assessed, inferring how changes in temperature and nutrients may alter dominant species in communities due to either increased or decreased parasite occurrence and subsequent levels of fitness.

Year 3.5

The last 6 months of the project will be for writing up and final analysis of the data. This time will be used to draw the experimental components together to get an idea of the changing landscape of parasite abundance, diversity and dynamics in response to historical and modern environmental changes.

& Skills

The student will gain training in field sampling from freshwater environments, molecular ecology, DNA extraction, PCR, high-throughput sequencing, bioinformatics, nutrient analysis advanced statistical analysis and population modelling.

References & further reading

Auld, S.K., Searle, C.L. and Duffy, M.A., 2017. Parasite transmission in a natural multihost–multiparasite community. Philosophical Transactions of the Royal Society B: Biological Sciences, 372(1719), p.20160097.
Bass, D., Rueckert, S., Stern, R., Cleary, A.C., Taylor, J.D., Ward, G.M. and Huys, R., 2021. Parasites, pathogens, and other symbionts of copepods. Trends in Parasitology, 37(10), pp.875-889.
Ebert, D., 2005. Ecology, epidemiology, and evolution of parasitism in Daphnia. National Library of Medicine.
Paplauskas, S., Brand, J. and Auld, S.K., 2021. Ecology directs host–parasite coevolutionary trajectories across Daphnia–microparasite populations. Nature Ecology & Evolution, 5(4), pp.480-486.
Skovgaard, A., 2014. Dirty tricks in the plankton: diversity and role of marine parasitic protists. Acta Protozoologica, 53(1).
Taylor, J.D. and Cunliffe, M., 2016. Multi-year assessment of coastal planktonic fungi reveals environmental drivers of diversity and abundance. The ISME journal, 10(9), pp.2118-2128.
Taylor, J.D. and Cunliffe, M., 2014. High‐throughput sequencing reveals neustonic and planktonic microbial eukaryote diversity in coastal waters. Journal of phycology, 50(5), pp.960-965.

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