Tag Archives: immune function

Your Immune Defenses Are What You Eat

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Condition‐dependent immune function in a freshwater snail revealed by stable isotopes (2022) Seppälä et al., Freshwater Biology, link to article

Image credit: Bj.schoenmakers, CC0, via Wikimedia Commons

The Crux

There are myriad factors at play when it comes to parasitic infections, but the primary physiological barrier for the parasite is the immune function of host organisms. Despite its importance and usefulness, the immune function is costly to maintain. Building and effectively using immune defenses relies on the host being able to secure enough food to properly fuel its defenses. As a result, individuals in poor condition are more susceptible to parasites. Building off of that, if the conditions in a given area are poor/worsening, then an entire population of organisms may be vulnerable to disease outbreak.

Many studies have investigated the dependence of immune function, including one of my own, but many of those studies take place in lab settings where the food given to a host is carefully controlled. While there are obvious benefits to controlling experimental conditions, it can be hard to generalize the findings of a lab study to the natural settings that organisms actually live in. Today’s authors utilized an observational study of a freshwater snail (Lymnaea stagnalis) to better relate host condition in nature to immune function.

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Measuring Immunity With Transparent Hosts

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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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Not Giving Into the (Selection) Pressure

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A common measure of prey immune function is not constrained by the cascading effects of predators (2021) Hasik et al., Evolutionary Ecology. https://doi.org/10.1007/s10682-021-10124-x

Image Credit: Adam Hasik, Image Cropped

The Crux

The immune function is a critical component of an organism’s ability to defend itself from parasites and disease. Without it, we would be in much worse shape when we got sick. Despite this usefulness, the immune function is costly to use as organisms have to consume enough food to have the energy needed to mount an immune response. This is easier said than done, however, and there are often many factors that come into play when it comes to acquiring energy.

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Bad Neighbors

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Image Credit: ksblack99, Public Domain, Image Cropped

Exposure to potentially cannibalistic conspecifics induces an increased immune response (2020) Murray et al., Ecological Entomology, https://doi.org/10.1111/een.12806

The Crux

Plasticity is a powerful force in nature that allows organisms to change the way they look, the way they act, and even their own physiological processes. Prey species commonly exhibit plastic responses when they are exposed to predators, and recent studies have shown that these predator-induced effects can affect the immune function of the prey species. Because of this, predators have the potential to modify disease dynamics, either increasing disease/parasite infection by reducing the prey’s immune function, or decreasing disease by increasing immune function.

Interestingly, predators are not the only organisms that consume prey species. Some prey species eat both members of their own trophic level (an intraguild predator, see Did You Know) and members of their own species (a cannibal). Because they act like a predator (by eating a prey organism), there’s a possibility that these cannibalistic individuals may have the same effect on their potential victims. Today’s authors used larval dragonflies to investigate that exact question.

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