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Body-snatching fungus hijacks cicada mating behaviour

It’s disappointing when your Friday night internet date doesn’t match their profile. But for male periodical cicadas this could mean their match is in thrall to a body-snatching fungus and they’re about to be the next victim.

In their recently published paper in  Nature Scientific Reports researchers observed that male periodical cicadas infected by the fungal parasite Massopora cicadina  flicked their wings like sexually receptive females, fooling males into trying to mate with them.

Illustration - Yessenia Carrero-UConn Illustration

The fungus infects the cicada and essentially hijacks their behavior.© Yessenia Carrero/UConn Illustration

What’s a bit of wing-flicking among friends? Well, it’s potentially fatal in male and female cicada’s when they mate with an infected insect. The fungal spores on the infected cicada cause the mate’s abdomen to eventually distend  and drop off taking the insect’s genitalia with it and its chance to mate.

Lead author, John Cooley, ecology and evolutionary biology researcher and adjunct faculty member at University of Connecticut said: “This phenomenon is the ultimate evolutionary arms race, where the host loses because they are rendered sterile or evolutionarily irrelevant by the fungus in order to spread the spores.”

Periodical cicadas emerge as adults every 13 or 17 years and Massopora cicadina is the only  known pathogen that is synced with their life cycle. It lies in wait for the cicada nymphs to emerge from the soil and infects up to five per cent of the population. These insects are at Stage I of the infection cycle and the cicada’s that are infected after mating are known as Stage II and suffer a similar fate.

Could this behaviour just be a symptom of infection rather than a deliberate attempt by the fungus to spread its spores?

The researchers only observed Stage I males showing both male and female sexual behaviour and  uninfected or Stage II males behaved as expected.  This caused them to speculate that this strange behaviour  isn’t a general symptom of the disease but, by some unknown means, the fungus adds a new skill to the cicadas mating behaviour to increase the chance of the spores being passed on.

The study authors used data gathered from observing the mating behaviour of both caged and free-flying cicadas and ran a series of small experiments, too small to be statistically valid,  where caged cicadas were played male mating songs.

In their paper the authors said that predicting where to find infected cicadas, especially Stage II infected cicadas, in sufficient numbers is a difficult task since infection rates vary over time and space. The best sites for studying  the insects had been almost stumbled upon. As Cooley explains, “I’d be driving along and say ‘Holy smoke, there are a lot of dead cicadas in this spot. What’s going on?'”

 

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