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