Has the evolution of complexity in the amphibian papilla influenced anuran speciation rates?

For anurans, increasing complexity of the inner ear has been correlated with speciation rates. The evolution of a complex amphibian papilla (AP) is thought to have facilitated speciation by extending the range of frequencies over which mating calls may diverge. Although this example has been proposed to represent a key innovation, the mechanism by which the AP is thought to promote speciation makes the questionable assumption that anurans generally use the AP for detection of their mating calls. This study uses mating calls from 852 species to test this assumption. Surprisingly, the calls of most species are not detected by the AP but by a second organ, the basilar papilla (BP). This refutes the role of AP complexity in facilitating call divergence and hence, speciation. Future research into the evolution of acoustically mediated reproductive isolation should focus instead on the BP as it may play a more critical role in anuran speciation.