From wasps to viruses, parasites are an important part of a healthy food web.
These are the eggs laid by cocoon bees on the larvae of the Pandora Sphinx Moth. From insects to birds, parasitic relationships are common. Photo by BATES LITTLEHALES, NAT GEO IMAGE COLLECTION
Written by: TROY FARAH
When it comes to parasites, many people are very disgusted, and few people are willing to share their bodies with parasites. The word "parasite" (from the Greek word meaning "eating next to") is enough to make people uncomfortable.
But Jimmy Bernot, an evolutionary biologist at the Smithsonian's National Museum of Natural History in Washington, D.C., said that as "a very successful life form," parasitic states should be more respected. From vampire bats to deep-sea squid, plants, animals, fungi, bacteria and viruses parasitize; small males cling to females forever.
Parasitism is a symbiotic form, the intimate relationship between two organisms. While some parasites, known as parasites, cause host death, many do not cause significant harm. Others even protect the host from other parasites, such as viruses that protect bacteria against antibiotics. However, if you're taking penicillin, that's not good news, and certainly great for those small pathogens.
There are many ways in which parasites take nutrients from their hosts: some are ectoparasites that suck directly on blood or eat the host's skin; others are in vivo parasites that make their home in the host, such as tapeworms and skin flies.
How many parasites are there in the world? Exact figures are not yet available, though some experts believe that the types of parasites far outnumber those of "independent" animals, and that most of the parasites may not have been discovered yet.
The parasitic hookworm clings to the caudal fin of the non-crucian carp in the mouth of Oriya. Photo by JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
In the Dannong Valley Conservation Area in Malaysian Borneo, a man is clearing leeches. Photo by MATTIAS KLUM, NAT GEO IMAGE COLLECTION
Given that parasites have burrowed into every crevice of life, it's no surprise that they have a long-term survival strategy. The earliest parasite in the fossil record– the host – was a worm that stole food from clam-like brachiopods 515 million years ago.
"When we looked at food webs or ecological webs, we found that in some cases, parasites maintain more than half of the links between species," says Mackenzie Kwak, a parasitologist at the National University of Singapore. ”
The story of the leech
Leeches are a worm and probably the most famous parasite. There are 700 species of leeches worldwide, but only about half of them suck blood. They are found everywhere on Earth except Antarctica, but the oceans around the Antarctic continent are also inhabited by leeches with tentacles that resemble fish leeches.
There are more ingenious ways for parasites. For example, the toad fly, which prefers to live in the nostrils of amphibians, or the shrunken-headed fish lice, is one of the few parasites that can replace the host organ by attaching to the fish's tongue.
In addition to feeding on the host, parasites have various ways to sterilize the host, invade the immune system, and even control the host's behavior. For example, some cordyceps fungi will turn insect hosts, such as ants, into "zombies", forcing them to climb higher above the ground and kill them, because the high place is the perfect place to spread fungal spores. The spores fall on the insects on the ground and begin a new cycle.
Some parasites steal resources indirectly. An example is the great cuckoo, a parasite that achieves the purpose of getting something for free by having other creatures raise offspring. They lay eggs in the nests of other birds, forcing those birds to raise their chicks for them.
Small but powerful
Some parasites, while seemingly inconspicuous, play a huge role in ecosystems. The small-nosed flower is a parasitic plant native to Europe that inserts its roots into the grass and sucks up their sap.
"Basically, when a wildflower meadow doesn't have small noseflowers, it becomes a prairie," Kwak explains, "however, once there are small noseflowers, it weakens these highly competitive grasses and allows wildflower meadows to grow a wide variety of flowers." ”
The small-nosed flowers replace grass with wildflowers, providing a living space for pollinators, which in turn attract birds and amphibians.
"They're actually the founders of the whole wildflower meadow, helping these sensitive wildflowers not to be eliminated," Kwak said.
Parasites
When one parasite parasitizes another, it is called a "reparsite," which is actually quite common. For example, the parasitic bee Hyposoter horticola will be met by another parasitic bee, Mesochorus cf. Stigmaticus parasitizes, the latter laying eggs in the larvae of the former.
In some rare cases, there are even super-reparasites, such as the fungus of the fungus that parasitizes the tree. In New Zealand, the fungus Rhinorichella globulifera feeds on the dead part of the fungus Hypomyces c.f. aurantius, which eats The Vibrio semi-gray pore fungus that lives on beech trees.
Rescue parasites
Despite the importance of the parasite, it is "strangely overlooked," said Jessica Stephenson, an assistant professor at the University of Pittsburgh. She is responsible for studying evolutionary parasitism.
Nematodontia fungus germinates from the carcass of an ant host. Photo by ANAND VARMA, NAT GEO IMAGE COLLECTION
For example, conservation projects often overlook these organisms. In many ways, parasites are more threatened than other organisms, especially climate change. First, global warming will directly affect them, such as the many mass extinctions in the past. There may be multiple parasites in a single host, and if the host becomes extinct, so many species of parasites may disappear.
"Given the high diversity of parasites, this means that most endangered species are parasites," Kwan and co-authors called for a "global parasite conservation plan" in a 2020 study. The paper proposes multiple ways to protect parasites, such as listing them as protected species.
"Almost every one of the endangered species I've observed has the same endangered parasites, and many of them are new," Kwak said.
For example, he was the first to document the endangered pangolin tick (Amblyomma javanense), a tick that lives on the critically endangered Malay pangolin in Southeast Asia. He also named the Stephanocircus domrowi ,one of Australia's rarest parasites, because they live in the critically endangered Lee's Bag Shrew.
The study notes that these protective measures do not apply to human and livestock parasites, such as Guinea worm nematodes; this parasite can invade human skin and cause exhaustive diseases.
But in many other cases, Kwak said, "these species don't necessarily cause harm to the host." They are just passengers on a long evolutionary journey... For the integrity and stability of ecosystems, they should be protected. ”
(Translator: Sky4)