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article imageLittle ‘coqui’ frog of Puerto Rico shows effect of climate change

By Igor I. Solar     May 21, 2014 in Science
A study on the differences in size and mating calls of a tiny Puerto Rican frog over a 23-year period suggests the male frog is getting smaller and its mating call becoming shorter and higher pitched. The differences may be caused by climate change.
The frogs known in Puerto Rico by the name "coqui" are some of the 186 species of the genus Eleutherodactylus inhabiting forests of southern United States, Mexico, Guatemala, and the Caribbean islands. There are 17 endemic species of coqui in Puerto Rico. For its abundance, the best known is the “Common Coqui” (Eleutherodactylus coqui). The species is named for the call that males produce. The call has two notes that sound like "Co" and "Qui" (hear it in video above). These sounds serve two purposes; "Co" serves to repel other males and establish a territory, while "Qui" serves to attract females.
Only male coquis sing. They start singing when the sun goes down at dusk, all night long until dawn. The Common Coqui is an animal of great importance in the culture of Puerto Rico and has become an unofficial symbol of the island.
The males are smaller than females. They measure an average of 27 millimetres while the females’ average size is 35 mm. However, as elevation increases, so does the size of the specimens. At higher locations in the forest, males grow to be nearly 50 mm and females about 60 mm.
In 1983, UCLA biology professor Peter M. Narins conducted an experiment in which he measured the pitch of the mating calls of 170 male coqui frogs, as well as their size, at different elevations in Puerto Rico’s El Yunque National Forest. What he found was that, as he went up in elevation, the frogs got bigger and their mating calls were slower in occurrence and lower in pitch compared to those of the frogs at lower elevations.
Twenty-three years later (2006), Narins returned to Puerto Rico and repeated the observations. Guided by the topographical maps he used two decades earlier, he measured the size and recorded the calls of 116 male coqui frogs along the road from about 10 yards above sea level to more than 1,100 yards above sea level.
El Yunque National Forest. Thirteen species of coqui frog  including the most common  Eleutherodacty...
El Yunque National Forest. Thirteen species of coqui frog, including the most common, Eleutherodactylus coqui, are endemic to Puerto Rico and live in El Yunque National Forest.
The average size of the frogs was smaller and their mating calls had grown faster and higher in pitch at every altitude. These changes were consistent with what may be expected in a warming environment. The results of this study became another contribution to the argument in support of climate change.
“All of the observed differences are consistent with a shift to higher elevations for the population, a well-known strategy for adapting to a rise in ambient temperature. Physiological responses to long-term temperature rises include reduction in individual body size and concomitantly, population biomass. These can have potentially dire consequences, as coqui frogs form an integral component of the food web in the Puerto Rican rainforest.” say the researchers in their report.
The research, entitled “Climate change and frog calls: long-term correlations along a tropical altitudinal gradient” authored by Peter Narins, Professor, Dept. of Ecology and Evolutionary Biology, UCLA, and Sebastiaan Meenderink, a UCLA physics researcher, was published online April 9 in the journal Proceedings of the Royal Society B.
More about Coqui frog, Puerto rico, common coqui, Eleutherodactylus coqui, El Yunque National Forest
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