As a general rule of thumb, most of the world’s wild animals keep their instinctual mating practices within their own species bubble. But if you’re a female plains spadefoot toad, then you just might consider dabbling with another species – so long as the male in question exhibits quality characteristics that make it an ideal mating candidate.
Image Credit: Stanley Trauth via Wikipedia
Citing a paper that was only recently published in the journal Science by a group of researchers from the University of North Carolina at Chapel Hill, it seems that the plains spadefoot toad sometimes bypasses potential male mates of its own species and instead opts to mate with males from another closely-related species called the Mexican spadefoot toad.
The researchers note that the male Mexican spadefoot toads aren’t being selected randomly by the female plains spadefoot toads, but rather by their quality. Based on the results of experiments conducted by the researchers, female plains spadefoot toads appear have a thing for males whose calls exhibit slower pulse rates, and male Mexican spadefoot toads often fit the bill whereas male plains spadefoot toads do not.
But why do the female plains spadefoot toads prefer males with slower call pulse rates? Your guess is as good as anyone else’s…
"Maybe a slower pulse rate means they're in better condition or is associated with certain genes linked to fitness," elucidated Catherine Chen, the paper’s first author. "But we can't say for sure right now."
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Many would be quick to assume that female Mexican spadefoot toads desire similarly preferred traits in potential male toad mates, but as it would seem, that’s not the case. Instead, female Mexican spadefoot toads favor males who make more frequent calls in a shorter period of time. This fact creates even more confusion in terms of understanding why the female plains spadefoot toads prefer the types of males that they do.
Perhaps unsurprisingly, a hybrid species results when a female plains spadefoot toad mates with a male Mexican spadefoot toad. Like many other hybrids that exist in nature, these hybrid toads aren’t without their quirks. They appear different when compared to either of the purebred species, and males are typically sterile. What’s more is the female hybrids don’t seem to have a preference for either species.
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While hybridization in and of itself isn’t a new concept, the idea that one species selects another species over its own because of one particular trait, is. By studying this behavior more closely, researchers may learn why the female plains spadefoot toads are selecting the alternate species to mate with, and the resulting discoveries could help us understand why hybridization occurs in the first place and how it impacts evolution.