Zombie Frogs Spread Killer Disease While Mating

Male Japanese tree frogs have more attractive mating calls when infected with the chytrid fungus.

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Male Japanese tree frogs infected with the chytrid fungus have stronger mating calls, which are more attractive to females. Via masaki ikeda/Wikipedia
John Virata

A disease that has devastated frog populations throughout much of the world may be spreading via frogs that the disease turns into zombies.

The disease, Batrachochytrium dendrobatidis (Bd) — also known as chytrid fungus — alters reproductive behaviors of male frogs, making their frog calls more attractive to females than non-infected frogs, yet makes them lethargic and all zombie-like at the same time, Science reports.

Initially scientists thought that frogs and other amphibians infected with the chytrid fungus died off because the disease causes an amphibian’s permeable skin to harden, but a new study in Biology Letters points to chytrid fungus induced altered behaviors of Japanese tree frogs that made the male calls of infected frogs more attractive to female frogs. This revelation complicates what is known about the disease and how it affects amphibians.

“Some people think that amphibian populations are declining primarily due to catastrophic die-offs caused by Bd,” Bruce Waldman, a behavioral ecologist at Seoul National University told Science. “But the story is much more complicated than that.”

The Rabbe’s fringe-limbed tree frog is believed to be extinct in the wild due to the chytrid fungus. There is only one such frog known to exist in the world, and it lives in the Atlanta Botanical Garden. Via Brian Gratwicke/Wikipedia

The Rabbe’s fringe-limbed tree frog is believed to be extinct in the wild due to the chytrid fungus. There is only one such frog known to exist in the world, and it lives in the Atlanta Botanical Garden. Via Brian Gratwicke/Wikipedia

Waldman and his student, the late Deuknam An, studied the mating calls of these frogs, thoroughly analyzing the calls of 42 frogs for pulses per note, repetition rate and number of notes as well as the call duration. Of the 42 frogs studied, nine of the frogs were infected with the chytrid fungus, and they noted that the infected frogs were slightly larger than the other frogs but also had a stronger frog call than the uninfected frogs. These stronger and faster calls are also more attractive to female frogs.

Although the infected frogs have a stronger mating call, the fungus also makes the frogs sluggish, causing the researchers to believe that the chytrid fungus acts like a parasite that eventually turns the infected frogs into zombies. And because they have a superior mating call than non-infected frogs, when they mate, they spread the disease to more frogs, which has adverse effects on the frog populations.

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