Tag Archives: daphnia

Measuring Immunity With Transparent Hosts

Host controls of within-host dynamics: insight from an invertebrate system (2021) Stewart Merrill et al., The American Naturalist. https://doi.org/10.1086/715355

This is a guest post by Dr. Tara Stewart Merrill

Image Credit: Per Harald Olsen, NTNU, CC BY 2.0, Image Cropped

The Crux

When it comes to understanding how parasites and pathogens spread, immune defenses may be an especially important factor. The immune system is the gatekeeper for parasites and pathogens (I’ll just use the term “pathogen” from here on out). Whether you are exposed to influenza, a parasitic worm, or a tick-borne bacterium, your immune response will determine the outcome of infection — either you will become infected (which benefits the pathogen’s reproduction) or you will not (which is a barrier to the pathogen’s reproduction). So now, picture a whole population of individuals. A room full of individuals with poor immune responses should result in more infections (and more transmission) than a room full of individuals with strong and robust immune defenses. By shaping the fate of pathogens, host immune defenses can shape transmission.

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Parasites: Maybe They’re Good?

Infection of filamentous phytoplankton by fungal parasites enhances herbivory in pelagic food webs (2020) Frenken et al., Limnology and Oceanography. https://doi.org/10.1002/lno.11474

Image Credit: MarekMiś, CC BY 4.0, Image Cropped

The Crux

Pelagic ecosystems (see Did You Know) make up more than 70% of the Earth’s surface, and the base of the food web is composed of primary producers like phytoplankton. Primary producers produce their own energy and provide an important service to the rest of the food web (and planet!). Not only do they provide a resource for the upper levels of the food web, but they also contribute to the global climate by making carbon available to other organisms. Because of these large-scale ramifications for any changes in phytoplankton primary production, many studies have investigated how things like nutrients, light, and temperature are able to affect phytoplankton.

A key aspect of certain phytoplankton is that they have morphological characteristics that make them more resistant to consumption by grazers further up the food web, like zooplankton. However, chytrid parasites (the same fungus that is ravaging amphibian populations the world over) are able to get around these defenses and reconnect phytoplankton to their zooplankton consumers. Chytrid infects phytoplankton, it then releases a free-living infectious stage, the zoospore, which is eaten by zooplankton. This indirect connection between inedible phytoplankton (like cyanobacteria) and zooplankton is called the mycoloop, and it can provide zooplankton with up to 40% of their food. Interestingly, studies have shown that zooplankton populations do better when their food, the inedible cyanobacteria, is infected by chytrid. Today’s study investigated how exactly chytrid is able to reduce the cyanobacteria defenses and provide zooplankton with more food.

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Monitoring Freshwater Populations in the Chernobyl Exclusion Zone

Radiation can have extremely negative effects on an individual. But is it as easy to measure its effects on an entire population? (Image Credit: Hnapel, CC BY-SA 4.0, Image Cropped)

Variation in chronic radiation exposure does not drive life history divergence among Daphnia populations across the Chernobyl Exclusion Zone (2019) Goodman et al., Ecology and Evolution, DOI: 10.1002/ece3.4931

The Crux

As anyone who has recently watched HBO’s Chernobyl can tell you, large doses of radiation are capable of doing some pretty serious damage to an organism. But whilst examining the effect of radiation on an individual might be simple, monitoring those effects on a population can be difficult. Whilst radiation negatively effects fitness, it can also help individuals with higher radiation tolerance to reproduce and dominate within the population of a single species, making it difficult to monitor the exact effects of radiation on that population. If a population is filled with only those who were strong enough to survive, you don’t get an idea of the variation in the radiation’s effects.

This week’s researchers tried to break through that problem by looking at different populations of a water flea in Chernobyl’s Exclusion Zone (CEZ) – the area still barred from entry in eastern Europe.

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