PESQUISA REVELA HIPERPARASITA QUE COMBATE O FUNGO DA FORMIGA-ZUMBI (com resenha)

A parasite that fights the zombie-ant fungus has yielded some of its secrets to an international research team led by Penn State's David Hughes. The research reveals, for the first time, how an entire ant colony is able to survive infestations by the zombie-ant fungus, which invades an ant's brain and causes it to march to its death at a mass grave near the ant colony, where the fungus spores erupt out of the ant's head. "In a case where biology is stranger than fiction, the parasite of the zombie-ant fungus is itself a fungus -- a hyperparasitic fungus that specializes in attacking the parasite that turns the ants into zombies," Hughes said. The research will be published in the journal PLoS ONE.

"The hyperparasitic fungus effectively castrates the zombie-ant fungus so it cannot spread its spores," said Hughes, who is an assistant professor of entomology and biology, and a member of the Center for Infectious Disease Dynamics at Penn State. "Because the hyperparasitic fungi prevents the infected zombie-ant fungus from spreading spores, fewer of the ants will become zombies."

As part of their research, the scientists created a detailed model that revealed previously unknown details of the interactions between the fungus-infected ants and the parasite-infected zombie-ant fungus. Scientists previously had known that ants defend their colonies against microscopic enemies such as fungal spores by efficiently grooming each other. In this study, the researchers also modeled the effect of ant behavior on limiting infection. "Interestingly, beyond the well known effect of defensive ant behavior, our new research reveals the added effect of the castrating actions of the hyperparasite fungi, which may result in significantly limiting the spread of the zombie-ant fungus" Hughes said.

The scientists report that only about 6.5 percent of the spore-producing organs of the zombie-ant fungus were viable. "Even though there are a lot of dead and infected zombie ants in the neighborhood, only a few of the spores of the zombie-ant fungus will become mature and able to infect healthy ants," Hughes said. "Our research indicates that the danger to the ant colony is much smaller than the high density of zombie-ant cadavers in the graveyard might suggest. This complex interaction between ant colonies, their brain-manipulating parasites, and other fungi capable of lending assistance to the colony underscores the need to study social insects under natural conditions." Hughes said his team is expanding its efforts and "remains focused on following the exciting theatre played out on the rainforest floor."

The research was performed by an international group of scientists from University of Copenhagen, Denmark, Federal University of Vicosa, Brazil and Penn State in the United States. The research is funded by a Marie Curie OIF Fellowship (PIOF-GA-2008-221041), Danish National Research Foundation and Brazilian National Council for Research (CNPq, grant no. 401610/2009-8) and Penn State.

Fonte : Penn State University

Resenha do autor – por Rafael Souza

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O fungo Ophiocordyceps unilateralis que foi descoberto por cientistas da Universidade da Pensilvânia , se infiltram no cérebro de algumas espécies de formicídeos de regiões tropicais afim de “manipular o seus corpos”.

O fungo contamina as formigas com seus esporos, no momento  em que elas descem para a parte mais fria e baixa da floresta.Os esporos infectam o animal por  inteiro, prejudicando seus membros e  o SNC(Sistema Nervoso Central ) de forma que obtêm um certo “controle” sobre a vitima , na qual induzem a formiga a partir em caminha a regiões que possuem solo úmido e frio, características ideais para a reprodução e crescimento do fungo.O comportamento das formigas é similar a de “zumbis”  de filmes de ficção, característica que lhe atribui o nome popular do fungo. Após alguns dias as hifas se estendem pelo corpo do animal já sem vida, o que torna visível a contaminação pelo fungo.Uma outra pesquisa realizada pelo Centro de Doenças Infecciosas da Universidade de Penn State, identificou um hiperparasita(vive como parasita sobre outro parasita) desse fungo.

Esse hiperparasita efetivamente impede o fungo de se reproduzir e espalhar seus esporos.Para um animal infectado isso não faz muita diferença, porém para uma colônia de formigas isso é relativamente positivo . Colônias de formigas em si já possuem uma boa defesa contra inimigos microscópicos de forma eficiente.

As relações inter especificas dessas espécies demonstrou um alto potencial para o estudo de comportamento animal de insetos, de maneira a estudar o comportamento da colônia sobre um manifestação de invasores microscópicos. 

O vídeo abaixo mostra outros insetos parasitados por fungos.

Referências : 

Eberly College Science
BUG GUIDE - Order Hymenoptera
Peter H. Raven & Ray F. Evert & Susan E. Eichhorn - Biologia Vegetal , Ed. Guanabara Koogan , 2007.