The mimic frog (Ranitomeya imitator) is the first vertebrate, and only the second known animal, to suggest that mimicry can split populations into separate species, according to a study published recently in Nature Communications. The other animal is a group of Heliconius butterflies, which are also found in South America.
We can’t hold the frog in our hands just yet, though—the new species may not finish evolving for several thousand more years.
Separate geographic populations of R. imitator can look wildly different, depending on the frog species they’re mimicking. In north-central Peru, two R. imitator populations colorfully masquerade as two contrasting poison frog species: The splash-back poison frog (R. variabilis) or red-headed poison frog (R. fantastica). (See more pictures of poison dart frogs.)
In a phenomenon known as Müllerian mimicry, which occurs when two or more poisonous or unpalatable species adopt the same colorful warning signal to predators, one of the R. imitator morphs—called “striped”—takes on the black-and-yellow stripes and marbled aqua legs of R. variabilis.
The other morph, or type—dubbed Varadero—has the orange head, black splotches, and blue legs of R. fantastica.
The study found that where these R.imitator morphs, which usually live apart, come into contact, the process of forming a new species begins.
Sticking With Their Own
The early signal of this process is that the two R. imitator morphs prefer to mate with their own type, according to the team’s observations in the wild.
In the experiments, scientists gave courting males the choice of a female from each morph, and then recorded the amount of courtship time between the male and each of the two female morphs to measure their preference.
“We think this will lead to speciation”—the process in which new species evolve—”but we’ll have to come back in a few thousand years to be sure,” said study co-author Kyle Summers, an evolutionary biologist at East Carolina University in Greenville, North Carolina.R. variabilis, one of the species mimicked by R. imitator, from the Cainarachi Valley, Peru. Photograph by Evan Twomey
Evidence that the morphs prefer to hook up with their own kind “suggests there has been some sort of negative consequence of breeding with the wrong morph,” said Summers, who received funding from National Geographic’s Committee for Research and Exploration.
Maybe “their offspring are less fit or they are more likely to be predated,” he added. “They have evolved this preference, but only where they’re likely to be at risk of making a mistake.” (See “New Frog Found—Has ‘Striking’ Color Change.”)
What’s more, the frogs’ ability to imitate is driving their genetic separation, the study team suspects, because the two morphs can use their elaborate patterns to tell each other apart.
Summers and colleagues’ past and ongoing studies into the vision of poison dart frogs make him “fairly confident that they can see the color pattern differences quite clearly,” he said.
James Mallet, an evolutionary biologist at Harvard University in Cambridge, Massachusetts, said that R. imitator’s ability to dramatically mimic different color patterns within various parts of its range is “amazing” and “very similar to what is happening in Ecuador and eastern Peru in the Heliconius butterflies.”
Mallet, who wasn’t involved in the new study, added that the finding that R.imitator’s mimicry switching is shown to be associated with mating behavior is “fascinating” and “gives an argument” for a new species in process.
But Mallet said that while color patterns are known to influence the mating decisions of some poison dart frogs, the new study “did not present any data showing that mate choice was based on color.” (See “Wild Romance: Weird Animal Courtship and Mating Rituals.”)
The distinct morphs “may be using some different signals, such as song,” he added.
Dealing with these frog masters of disguise, it was always going to be difficult to tell.