Listen, most people are not huge fans of parasites. Whether it’s the tongue-replacing kind, the live-in-your-gut-and-eat-your-food kind, or really, any of them, they tend to inspire the heebie-jeebies. And more often than not, they do a number on the health of their hosts, so it’s hard for us to think of them as a positive influence on the world.
But research from 2020 suggests that thanks to climate change and other factors, overall parasite populations are decreasing. And that could actually be a really bad thing. Parasitism is a way of life, and not limited to any one group of organisms. It’s a strategy, not a family. And it’s a pretty simple one. If you’re living in, or on, a host and getting your food from their bodies at their expense, you’re a parasite.
Parasitism is one of the most common life strategies to evolve across a huge range of organisms from the microscopic to many meters long, making it one of the most abundant and hugely diverse forms of life on Earth. Since parasitism has evolved many times over, exactly how each kind does its thing varies. Some parasites live inside their host while others simply latch on. And it gets even more complicated, because many parasites require a host in order to grow from an egg to an adult. Plus, some even need more than one host, hopping from species to species depending on the stage of their life cycle. Some even need three separate hosts through their various life stages!
And while we may think of them as unwanted in pretty much every scenario, parasites are deeply interwoven into food webs and ecosystems, and their presence can actually be beneficial. These benefits obviously don’t apply to the individuals who have parasites, since a higher parasite load is strongly correlated with worse health. But the pressure those parasites put on populations can have really big impacts by keeping ecosystems in check.
Take invasive species. Invasive species are really good at taking over ecosystems. It’s kind of what they’re known for. But it’s possible that the reason they don’t wreak havoc on the ecosystems where they came from has to do with parasites. Parasites can help prevent any one species from becoming too dominant, by keeping their host species’ growth at a reasonable level relative to the other organisms in the ecosystem. And escaping their natural parasites might be one of the reasons that some species become invasive in the first place.
Some researchers have also hypothesized that as hosts evolve to outfox their parasites, the selective pressure created by those parasites causes more speciation and diversity, which is beneficial for the ecosystem overall. So the greater the diversity of parasites present, the more stable and resilient ecosystems may become.
The problem is, thousands or even millions of parasite species may be at risk of extinction without us even knowing it. And, the impact of their disappearance could radiate through their ecosystems in dramatic ways. See, unless the parasites are infecting us or domesticated animals like pets and livestock, we haven’t exactly been invested in studying them or their ecological importance. So we have almost no long term data on parasite population trends, other than the ones that affect us. And there’s a core site in Frankfurt.
Even though we may want to help save parasites, we lack the understanding of their roles in the ecosystem and long-term population trends to know where to start. However, a study published in 2023 looked into the changes in parasite populations over time due to their preservation in natural history collections. The study examined 139 years’ worth of fish specimens from Puget Sound on the northwest coast of the United States. Since the fish had all been preserved whole and un-dissected, their parasites were also preserved alongside them. This allowed the researchers to measure the parasite load of the fish populations over time.
The study found that the majority of parasite species were decreasing in numbers. Specifically, parasites that required three or more hosts as part of their life cycle were declining at a rate of over 10 percent every decade. It was also discovered that there was a correlation between the decline of the multi-host parasites and an increase in sea surface temperature.
Since parasites rely on their hosts for survival, if the host species suffers, so do the parasites. If a parasite species requires multiple hosts for their life cycle, then a delicate balance must be maintained in order for it to survive. This is bad news for parasites, given that living through multiple hosts is a very common strategy for them. One study predicted that if just 5 of North America’s carnivores went extinct, 56 parasite species would be lost with them.
Parasite ecologists have been trying to draw attention to this issue for decades, and it’s about time we start worrying about their decline as well. In 2020, a group of researchers developed a global conservation plan for parasites to help guide efforts over the coming decade. This includes increasing education and pinpointing where to focus research efforts and legal protections.
Even though parasites aren’t built for cute logos or cheerful conservation slogans, we still need to make an effort to protect the less glamorous, yet equally important, species. If we are serious about biodiversity conservation, then we need to do some PR work to get people on board with protecting parasites. They are aiming to expand their existing data centers by at least 12 more by the end of 2023. To get started with their new servers, click the link in the description below or head over to linode.com/scishow to get a $100 60-day credit on a new Linode account. Thank you for watching from all over the world! [OUTRO]