A study of various colored poison-dart frogs suggests that mating behaviors of green versus red frogs of the same species are not exactly the same.
Beatriz Willink of the University of Costa Rica led the research, which sought to determine if green variants of granular posion frogs were more or less conspicuous to potential mates and predators than red frogs of the same species (Oophaga granulifera).
The bright colors of the poison-dart frogs serve not only to attract potential mates, but also to ward off predators, such as birds, by signaling to the predators that the amphibians are poisonous. A red poison-dart frog, it is assumed, has a competitive advantage over a green one because the red coloration is a clear warning sign to predators that it is poisonous.
To test the frogs, Willink and her collaborators measured how the colorful skin of the frogs contrasted against the natural background in the southwestern lowlands of Costa Rica. They chose to test the frogs based on color because at least one species of poison-dart frog is known to make mating choices influenced by skin color. The research team also measured the mating call activity of both red and green poison-dart frogs to account for whether green-colored frogs adjust their actions based on the availability of potential mates.
The study's results revealed that green-colored frogs, despite being less visible in some cases, can appear as bright as red frogs to members of their own species, but not to birds.
"Green frogs therefore seem to adjust their sexual behavior accordingly: They can deliver relatively conspicuous signals to females while being less conspicuous to potential predators," the researchers said in a news release.
The team found that green males vocalized mating calls less frequently than red males when advertising to distant females. But if a female was within close range, the team found that the green frogs vocalized as much as their red counterparts.
In the right context, the researchers concluded, green male poison-dart frogs appear to see a trade-off in the risk of predation versus the benefit of securing a mate by drawing attention to itself.
"Our results support the notion that populations of phenotypically or observably different divergent species may use different solutions to the trade-off between natural and sexual selection, by adjusting the place and time of displays to risks and opportunities," Willink said. "In poison frogs this may have contributed to the dramatic variation in color pattern conspicuousness observed across species."
The research is published in the journal Behavioral Ecology and Sociobiology.