As it quickly became clear in late February and early March that COVID-19 was not going away anytime soon, attention turned to trying to figure out when and where the virus would spread. Epidemiologists and virologists have had their work cut out for them, trying to simultaneously reassure and warn people the world over about the dangers, the nature and the potential timeline of the virus.
So it came as somewhat of a surprise to see ecologists try and tip their hat into the ring. Early on in the pandemic, teams of ecologists sprang up, trying to use Species Distribution Models to predict the spread of the virus. And whilst this might sound helpful, many of these studies lacked collaboration with epidemiologists, and their predictions very quickly fell flat. Some studies suggested that areas like Brazil and Central Africa would be largely spared by the virus, which quickly turned out not to be the case. Flaws in the studies were spotted quite quickly by concerned members of both the ecological and epidemiological communities alike, and a few teams got started on responses.
Image Credit: Mislav Marohnić, CC BY 2.0, Image Cropped
If you’re unlucky, you already know that humans possess a skin microbiome. It sounds gross, but it’s simply an entire ecosystem of microbes like bacteria living on our skin (maybe it is gross). Some of them help us, others might make us sick, for example when they enter open wounds. Plants have a similar set-up, hosting different ecosystems of bacteria on their leaves.
Hopefully, at this point I’ve made your skin crawl (because as you now know, it is literally crawling). But that microbiome can actually tell us some fascinating things about the animal or plant we’re looking at. So today, I’ll go through exactly what metagenomics is, and some of the information we can glean from a plant’s surface (I am a botanist after all).
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
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).
Image Credit: The Witcher, 2020
Science and movies often don’t go well together*. It’s no-one’s fault. Science can often be boring and riddled with uncertainties, and movies and TV require plot advancement and definitive results.
But you know what’s a scientific fact? That Henry Cavill’s chin can cut diamond, and if you thrust him into a cosplay outift he probably already had at home and send him out to slaughter a bunch of CGI monsters you’ll get something that is at the very least mildly enjoyable. And if you’re an invasion ecologist who runs a podcast looking at the ecology of movie monsters, mildly enjoyable monsters are enough to dedicate a blog post to.
Many organisms are vulnerable to a wide array of diseases and parasites throughout the course of their lives, but could scavengers help reduce that vulnerability? (Image Credit: The High Fin Sperm Whale, CC BY-SA 4.0, Image Cropped)
Do scavengers prevent or promote disease transmission? The
effect of invertebrate scavenging on Ranavirus transmission (2019) Le Sage et al., Functional Ecology, https://doi.org/10.1111/1365-2435.13335
As intimate as the host-parasite relationship is, it is important to keep in mind that it is embedded within a complex web of other interactions within the local ecological community. To add to this complexity, all of these interactions can feed back on and effect the host-parasite relationship. One ubiquitous part of all communities is the scavenger, an organism that feeds on dead and decomposing organisms. The authors of this paper wanted to investigate how scavengers affect disease transmission in local communities.
This question in interesting because it can easily go either way, depending on the community in question. Scavengers could lower disease transmission by eating infected organisms, thus removing contagious elements from the environment. However, scavengers could also increase transmission by promoting the spread of contagious elements in the community via their own waste after they consume infected tissues.
Fields full of herbaceous plants such as these can be incredibly diverse and complicated ecosystems, and the multitudes of species that inhabit them can influence the magnitude of disease that the organisms that inhabit it may encounter (Image Credit: LudwigSebastianMicheler, CC BY-SA 4.0, Image Cropped)
Past is prologue: host community assembly and the risk of infectious disease over time (2018) Halliday, F.W. et al., Ecology Letters, 22, https://dx.doi/10.1111/ele.13176
Everything in ecology is based around the environment that a focal organism inhabits, including the interactions it has with other organisms and the non-living aspects of the habitat itself (temperature, water pH, etc.). That being said, it’s no surprise that disease dynamics are likely to depend on the environment that a host inhabits, and that the environment itself is a product of what came before. That is to say, the group of organisms that originally populate a given ecosystem can have an effect on how that ecosystem will look in the future (lakes with freshwater mussels will have clearer water than those without).
The scientific literature is full of experiments, observations, and hypotheses about which environmental conditions lead to fluctuations in disease dynamics. As such, it is difficult to come to a consensus with a “one-size-fits-all” rule for disease dynamics and community structure. The authors of today’s study used a long-term experiment to determine what exactly moderates disease over time. Read more
Image Credit: Gilles San Martin, CC BY-SA 2.0, Image Cropped
Immune response increases predation risk (2012) Otti et al., Evolution 66
Parasites and diseases cause a lot of problems for their hosts, stealing resources like blood, food and energy. But fighting off parasites is also a costly process, so hosts have to walk the thin line between using just enough resources to fight off the parasite and using too many, leaving them with nothing. The amount a host invests in their immune response will depend on the specific environment that they live in. For example, in an environment where resources are plentiful, a host may decide that it is worth shaking off a parasite or disease. In areas where resources aren’t, they may choose to save energy.
Introducing predation to a situation further complicates things. Having a lot of predators around naturally means energy conservation becomes even more important. This study examines the risk of predation for an organism that is fighting off an infection.