Tag Archives: chytrid

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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Protection from Two Enemies with One Defense

Image Credit: Connor Long, CC BY-NC-SA 3.0, Image Cropped

Of poisons and parasites—the defensive role of tetrodotoxin against infections in newts (2018) Johnson et al., Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.12816

The Crux

Many organisms in nature produce powerful (and sometimes deadly) toxic substances, often taken as evidence that prey evolved chemical defenses against predators. Interestingly, these chemical defenses are deadly not only to predators, but also to parasites. This complementary defense, in addition to the ubiquity of parasites themselves, indicate that parasites may have had a hand in the evolution of host toxicity.

One particularly potent toxin found in the animal kingdom is tetrodotoxin (TTX). It can cause paralysis, difficulty with breathing, and even death in some cases. Newts in the genus Taricha are notorious for having high concentrations of TTX in their skin and eggs, and this has long been thought to have evolved as a defense against predators. In particular, Taricha newts and garter snakes (Thamnopholis spp.) are a classic example of arms-race dynamics (see Did You Know). Despite this relationship, newt toxicity and snake resistance to the toxin don’t always match up perfectly in nature, suggesting that other factors may influence newt toxicitiy. The goal of today’s study was to study parasitic infection and compare it to variation in toxicity among two newt species, the rough-skinned newt (T. granulosa) and the California newt (T. torosa).

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