Pumpkin toadlets, found in the leaf litter of Brazil’s Atlantic forest, are among the smallest frogs in the world. An international team has discovered that two species of these tiny orange frogs are unable to perceive the sound of their own calls, according to an announcement on the University of Cambridge website. Lead author Sandra Goutte and her colleagues, including Dr Matt Mason, showed this through multiple lines of inquiry including the failure of the frogs to respond behaviorally to call playback and the lack of auditory brainstem response to the call frequencies.
Work done by Mason included making 3D reconstructions of the inner ears of these tiny frogs to demonstrate that the basilar papilla, the organ of the inner ear used to process high-frequency sound, is undeveloped.
Most male frogs call to signal their presence to the opposite sex and find a mate, but this is costly: it could attract predators and parasites, and it uses up energy and time. One would think that if a signal is not perceived by its target audience, it would be lost through evolution.
The discovery that these frogs are not sensitive to the sound frequencies of their own calls is a unique case in the animal kingdom of a communication signal persisting even after the target audience has lost the ability to detect it! Perhaps the frogs are using visual cues instead to communicate. The lack of sensitivity to their own calls in these pumpkin toadlets appears to be an example of evolution “in the making.”
Original Paper: Goutte S, Mason MJ, Christensen-Dalsgaard J, et al. Evidence of auditory insensitivity to vocalization frequencies in two frogs. Scientific Reports. September 21, 2017; 7(12121). doi:10.1038/s41598-017-12145-5
Source: University of Cambridge, Scientific Reports
Images: University of Cambridge courtesy of Dr Sandra Goutte