The parasites that turn spiders into zombies – 11/20/2023 – Science

In the middle of the forest, on the leaves of trees about one meter from the ground, whitish spots could be seen as bird droppings from a distance.

Closer up, they are velvety mounds that sometimes retain characteristics of the spider that once existed, and sometimes display only tiny shapes with something alien. They are reproductive structures of fungi that specialize in parasitizing spiders.

Similar parasitism in ants inspired the electronic game “The Last of Us”, which includes devouring creatures infected by a mutant fungus and this year became a television series.

He adds that Brazil is one of the countries with the greatest diversity of parasitic fungi in the world. “The Amazon and the Atlantic Forest are ‘gold mines’ for those who study these fungi,” he says. “Sometimes the majority of the day’s collections are species we don’t yet know about.”

Sobczak highlights that the findings in the Northeast region make it clear that there was a forest connection from the south to the north of the country. “We found the same species of fungus, associated with the same host, in Ceará, Amazonas and the Ribeira Valley, between São Paulo and Paraná”, he explains.

The main location of his research is the Serra do Baturité, an area of ​​Atlantic Forest in the northeast of the state in the semi-arid region, where the Caatinga predominates.

“We found a high incidence of parasitism under the leaves and on the bromeliads”, says the ecologist. “We saw wasps, ants, beetles, crickets – there is evidence that it is one of the richest areas in entomopathogenic and araneopathogenic fungi.” It refers to insect and spider parasites, respectively.

After the inventories comes the part of understanding the action mechanisms, which are still undefined. The constancy in the mode of death, however, makes it clear that there must be an adaptive advantage for the fungus.

“Regardless of the species, all spiders die in a similar place, attached to the underside of the leaves.” The researcher states that a study coordinated by him and conducted by ecologist Ítalo Arruda, from the Federal University of Ceará, is convincing evidence that the fungus induces spiders to climb the highest plants.

On average, the parasitized ones die stretched out on the leaves about 1 m from the ground, while the healthy ones make silk shelters 75 centimeters high, as described in a 2021 article on Canadian Journal of Zoology.

“The parasite manipulates the behavior of the hosts in order to provide a great advantage to the fungus”, explains biologist Aristóteles Góes Neto, coordinator of the Laboratory of Molecular and Computational Biology of Fungi at the Federal University of Minas Gerais (UFMG).

Manipulation generally involves spiders climbing trees and settling on leaves higher than those where they would normally stay and then dying there.

“They’re like real-life zombies”, jokes the researcher. From this position, the fungi’s reproductive structures release spores that fall like a shower of microscopic dust and spread over future victims, on the lower leaves.

The group from Minas Gerais published in April, in the scientific magazine Journal of Fungi, a survey on the parasite genus Gibellula –it was the doctoral work of biologist Thairine Mendes Pereira, contributing to discovering this association.

“It is one of the only genera of fungi that only parasitize spiders”, explains Góes Neto. In addition to a bibliographical survey, the fieldwork consisted of searching the vegetation in the Rio Doce State Park, in Minas Gerais, at the Santa Lúcia Biological Station and the Augusto Ruschi Biological Reserve, the last two in Espírito Santo.

The biologist also looked for parasitized spiders in Ceará, in partnership with ecologist Jober Sobczak, from Unila (Federal University for the International Integration of Afro-Brazilian Lusofonia). In the Ceará municipality of Pacoti, they found a fungus that, when invading the spider, coats it with golden hyphae (fungal filaments) – which is why it was named G. aureaas described in a 2022 article on Phytotaxa.

“It is difficult to identify the spider after the spores have formed because the fungus destroys the host’s body,” explains Sobczak. When legs can be counted, researchers distinguish arachnids from insects, but more detailed identification of spiders often depends on examining genitalia.

The relationship has already been extensively studied in insects, but worldwide it is still largely unknown for spiders.

“This area in mycology [estudo de fungos] is still very little explored, but a considerable part of the studies is coming from Brazil through the work of professors Ari, from UFMG, and Jober Sobczak, from Ceará”, says Brazilian mycologist João Araújo, curator of fungi at the New York Botanical Garden, in the U.S.

He has collaborated with groups based in Brazil to describe the species, define the kinship relationships between them and elucidate their biology and evolution. “We are still in our infancy in terms of understanding the real biodiversity related to these fungi.”

He adds that Brazil is one of the countries with the greatest diversity of parasitic fungi in the world. “The Amazon and the Atlantic Forest are ‘gold mines’ for those who study these fungi,” he says. “Sometimes the majority of the day’s collections are species we don’t yet know about.”

Sobczak highlights that the findings in the Northeast region make it clear that there was a forest connection from the south to the north of the country. “We found the same species of fungus, associated with the same host, in Ceará, Amazonas and the Ribeira Valley, between São Paulo and Paraná”, he explains.

The main location of his research is the Serra do Baturité, an area of ​​Atlantic Forest in the northeast of the state in the semi-arid region, where the Caatinga predominates.

“We found a high incidence of parasitism under the leaves and on the bromeliads”, says the ecologist. “We saw wasps, ants, beetles, crickets – there is evidence that it is one of the richest areas in entomopathogenic and araneopathogenic fungi.” It refers to insect and spider parasites, respectively.

After the inventories comes the part of understanding the action mechanisms, which are still undefined. The constancy in the mode of death, however, makes it clear that there must be an adaptive advantage for the fungus.

“Regardless of the species, all spiders die in a similar place, attached to the underside of the leaves.”

The researcher states that a study coordinated by him and conducted by ecologist Ítalo Arruda, from the Federal University of Ceará, is convincing evidence that the fungus induces spiders to climb the highest plants. On average, the parasitized ones die stretched out on the leaves about 1 m from the ground, while the healthy ones make silk shelters 75 centimeters high, as described in a 2021 article on Canadian Journal of Zoology.

Researchers still don’t know exactly how the fungus advances through the spiders’ organism after infection, but Góes Neto infers that it is similar to what has already been observed in insects, in which the fungus produces compounds that act on the invertebrate’s neurons and cause the change. of behavior.

“We have already sequenced the complete genome of G. pulchrathe species of fungus with the widest distribution, and we found several genes possibly involved with interference in the nervous system”, he adds, about work still in progress.