Frog Survival, But More Trouble

What doesn’t kill you makes you… more attractive? That might be how the saying goes for male Japanese tree frogs (Hyla japonica) who aren’t killed by the deadly chytrid fungus and disease, but rather invest more energy into their mating calls.

A few weeks ago, we provided an update on research into chytrid, which has caused amphibian death and extinctions worldwide for several decades now. Scientists understand that some frog species are able to survive this pathogen and study these animals to understand how they’re doing it, and why.

Bruce Waldman of Seoul National University and his colleagues studied the calls of one such survivor species, Japanese tree frogs in South Korea. Chytrid (also known as Batrachochytrium dendrobatidis, or Bd) has been infecting amphibians in that area for at least a century, the team writes in a study published last week in Biology Letters, “Over time, frogs presumably have adjusted their life-history strategies to compensate for the effects of the pathogen.”

One of those adjustments, the researchers discovered, are longer and more frequent calls by the male frogs. Turns out those types of calls are just the ones that female Japanese tree frogs prefer. So chytrid is making the frogs more attractive and improving their rates of surviving, at least genetically. While the frogs may survive the pathogen, infected animals do have shorter lifespans. Perhaps that’s why the longer, more frequent (and could one say desperate?) calls. The team writes: “Increased calling may have resulted from selection on infected males to reproduce earlier because of their shortened expected lifespan.”

Another reason could have more to do with the fungus, and not the frog. Chytrid could be manipulating the frogs to call more attractively, getting the frogs to mate more often and spread the fungus more rapidly. (Reminds us of the zombifying ant fungus we’ve written about before.)

So surviving chytrid may not be good in the long run, the researchers say. “Our results raise the possibility that sublethal effects of Bd alter amphibian life histories, which contributes to long-term population declines.”

Image: 夢の散歩/Wikimedia