Terrestrial flatworms (or platyhelminthes) reason vital ecological harm in France, as those species don’t have any predators in France. Will the new discovery of parasites permit the struggle towards those species?
For approximately ten years, we have now been learning the invasion of terrestrial flatworms (or platyhelminths) in France and Europe. Those unique animals, generally so long as a finger, arrived in Europe through transporting potted crops. About ten species at the moment are with us, most commonly from the southern hemisphere (Argentina, Australia, New Guinea, Southeast Asia). They most commonly settled within the gardens, particularly the Obama nungara, which is now provide in additional than 70 departments. Others are identified to the general public, corresponding to Bipalium kevense, which will achieve about thirty centimeters, or Vermiviatum covidum.
When a species invades an ecosystem, it continuously reasons a variety of ecological issues. Terrestrial platyhelminths are predators, and we all know that they consume (particularly in terms of the Obama weevil) earthworms, those valuable allies of the gardener for soil fertility.
The well-known concept of “releasing enemy pressure”
And right here the query arises, tips on how to struggle towards those invaders? Since no chemical product has been authorized and even examined, let’s fail to remember this answer instantly. Predators that may consume those worms? We do not know of any in Europe. Parasites that would restrict their proliferation? Unknown too.
Scientists who find out about invasions normally suppose that an invasive species leaves predators and parasites at the back of when it reaches a brand new territory, which eliminates any brake on its unfold: that is the “enemy pressure relaxation” concept. That is certainly the case with terrestrial platyhelminths in France and Europe.
Discovery of parasites
We have been startled to seek out the primary strains of parasites in invasive terrestrial platyhelminths. However, as you’re going to learn, this discovery used to be now not as simple as one may believe.
We’ve now not noticed those parasites. So how have been they found out? We’ve been accomplishing molecular research of terrestrial platyhelminths for a number of years. Specifically, we have now described, now not all the genome, which might be very lengthy and costly, however the mitochondrial genome of greater than ten species.
The mitochondrial genome, or mitogenome, is what permits the functioning of mitochondria, those small parts found in all cells. In platyhelminths, the organs are embedded in a cushy tissue referred to as parenchyma. So after we analyze a person, we get now not handiest its personal DNA, but in addition the DNA of its prey discovered within the intestine. This permits us to higher perceive their nutrition through figuring out the species ate up.
So right here we do a regimen research of 2 species present in Northern Eire, Kontikia andersoni and Australoplana sanguinea. Those two species come from Australia and New Zealand and feature invaded the British Isles, however now not (but) mainland Europe. The analyzes briefly made it imaginable to symbolize the mitogenomes of platyhelminths and to decide their prey, which in each circumstances are earthworms. However we have been in for a marvel.
Parasitic mitogenomes?
In each and every species of platyhelminth, we discovered a molecular sign from a species of the genus Mitosporidium. Till now, the genus Mitosporidium contained just one species, Mitosporidium daphniae, which is a parasite of daphnia, a small freshwater crustacean. Mitosporidium may be very authentic: this can be a “primitive” microsporidia. What are microsporidia? Unicellular parasites.
A microsporidia turned into infamous within the Eighties, Enterocytozoon bieneusi, which inflamed immunocompromised AIDS sufferers. Prior to molecular genetics, microsporidia have been categorized as “protozoa” and identified through their very unique spores. We’ve since discovered that those are fungi which might be extremely changed through parasitism, specifically through the lack of mitochondria.
As discussed above, mitochondria are organelles found in all eukaryotic cells, however microsporidia, which are living within the cells in their hosts, not want them and have got rid of them.
A standard microsporidium spore, stained to turn inner constructions. Jaroenlak et al., 2020, CC BI
However nature loves exceptions, and scientists love exceptions after they permit us to higher perceive nature… Mitosporidium daphniae has the entire traits of a microsporidium, with the exception of that it has retained its mitochondrial genome. Subsequently, we imagine this species “basal”: it will constitute a level within the evolution of fungi against microsporidia, which already has the morphology and intracellular lifetime of microsporidia, however has retained the mitogen.
And so, we discovered two new species of Mitosporidium, one in each and every species of flatworm. The mere growth of this genus from one species to 3 used to be already an important discovery; the one identified species used to be described in 2014, and none since.
Mitochondrial genomes of 2 species of microsporidia have been found out. Gastineau et al, CC BI Parasites of what?
A large drawback arose. For technical causes we didn’t see microsporidia. They’re simply identified handiest when they’re within the spore level, and different phases, within the host’s tissues, are tricky to discover. And above all, the query arose: on whom do those microsporia parasitize? Consider, our research used to be accomplished on a mix of tissues: tissue from the predatory platyhelminth and tissue from the malicious program in its intestine. Had been those mitosporidium parasites of the platyhelminths themselves or in their prey, the earthworm?
For now, we can not definitively come to a decision, however we’re guided through a organic idea: parasitic specificity. Certainly, a parasite is continuously related to a unmarried host species. Alternatively, we discovered a singular species of Mitosporidium in each and every studied terrestrial platyhelminth.
Two hypotheses are imaginable. Or those parasites come from earthworms that consume earthworms – however then we must admit an out of this world accident: that each and every platyhelminth ate one form of earthworm, and turned into inflamed with its personal particular parasite. Or, extra merely, each and every platyhelminth has its personal mitosporidium. It’s this 2nd speculation that turns out possibly to us, pending a much broader research.
The long run for combating flatworms?
We suppose, subsequently, that we have got now found out invasive flatworm parasites. Consistent with the overall concept of “hostile pressure release,” one approach to do away with an invasive species is to contaminate it with a parasite or pathogen that can scale back its inhabitants. A vintage instance is that of the rabbit in Australia: free of its predators and parasites, it multiplied uncontrollably and handiest the advent of myxomatosis allowed its inhabitants to lower fairly. However it isn’t all the time simple: a number of parasites had been known for the Asian hornet, invasive in Europe, none of that have been in a position to truly decelerate its growth.
Introduce microsporidia to scale back populations of invasive terrestrial platyhelminths? An exquisite concept, however we’re very a ways from it.
First, as defined above, we’re nonetheless now not positive that Mitosporidium are parasites of platyhelminths. Then, we do not even know if they’re pathogenic! The one identified species prior to our paintings, Mitosporidium daphniae, has just a small detrimental impact at the fecundity of inflamed daphnia. Years of study are nonetheless wanted.
