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As amphibians, toads prefer humid environments. During dry periods, populations living in arid regions hide in underground shelters, which maintain humidity, from which they emerge when the rain returns. An international team led by a researcher from the National Museum of Natural Sciences (MNCN-CSIC) has carried out an experiment to understand how they use seismic detectors in their inner ear.
"When approaching this study, we ask ourselves how do the toads know that it is raining if the underground soil where they shelter is already wet," says Rafael Márquez, a researcher at the MNCN. "We used the hypothesis that they are capable of detecting low-frequency vibrations and we developed an experiment to test it," he continues.
Toads of both species exposed to the vibration stimulus emerged much faster than toads that did not receive it.
For the study, published in Current Biology, the scientists visited the sand dunes in the Doñana Natural Park (Huelva), captured toads of two different species (spur toads, Pelobates cultripes, and running toads, Bufo calamita) and built enclosures in the dunes where they were buried.
On nights without rain, using pre-recorded rain vibrations emitted by a tactile transducer (device capable of generating vibrations in the substrate) buried 10 centimeters underground, they were able to reproduce the vibrations and monitor the appearance of amphibians.
Toads of both species exposed to the vibration stimulus emerged much faster than toads that did not receive it. Specifically, the toads in the experimental group emerged about 26 minutes earlier. In addition to emerging earlier, the total number of toads that emerged from their shelters was higher in the stimulated groups.
“This research allows us to understand the role of the special organs for detecting vibrations in the substrate that toads have in the inner ear. Likewise, the results suggest that the detection of small vibrations is biologically relevant and probably generalized in anurans from arid zones. The seismic dimension of the sensory world of frogs and toads can have important consequences for measuring the impact that human activities can have on this highly threatened group of vertebrates ”, concludes Márquez.
R. Márquez, J.F. Beltrán, D. Llusia, M. Penna, and P.M. Narins. "Synthetic rainfall vibrations evoke toad emergence." Current Biology DOI: http://dx.doi.org/10.1016/j.cub.2016.11.00