We’re in Arizona’s Sonoran desert, listening to a lone spadefoot toad trying to lure females with his mating call. I’m Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History.
Karin Pfennig is a biologist at the University of North Carolina in Chapel Hill.
“Calls require a lot of energy. One possibility is that call rate, or how fast a male can call, could signal to a female that male’s condition. So if a female could maybe cue in on a fast call rate, then that male may be in higher condition because he can call fast and so he may be in overall better condition, may have better sperm quality, things like that.”
But what sounds like a male spadefoot toad with fast calls could also be a different species altogether. Female toads apparently know this and act accordingly.
“What we find in female preference tests is that they actually prefer average call rates. And presumably, that’s because if they start preferring faster call rates, those fast call rates actually start resembling another species of spadefoot. That if they were to mate with they would not produce very healthy offspring. So what it looks like is when female are there with other species of spadefoot, these southern spadefoot females look like they’re compromising on the quality of the male, in order to ensure that they mate with their own species of male.”
In other words, even though these discerning female toads may recognize that a faster call indicates a more potent male, they’ll still go for the toad with the slower calling rate, because he’s more likely to be their species– their kind of toad.
Pulse of the Planet is presented by the American Museum of Natural History. Additional funding for this series has been provided by the National Science Foundation. I’m Jim Metzner.