Meeting Abstract
Convergent evolution of novel traits can be adaptive, such as the loss of costly and superfluous sensory structures in cavefish and snakes. But, examples that apparently lack adaptive explanations also exist. For example, middle ear structures have disappeared among true toads (Bufonidae) at least 10 times, even though toads, like most anurans, primarily communicate with sound. To better understand these ear transitions despite the importance of acoustic communication, we have investigated whether there is consistency in the ways that earlessness develops in different lineages within the bufonid clade. We explored the behavior and developmental morphology of related pairs of eared and earless toad species using field observations and 3D reconstruction of developmental series resulting from captive breeding in Peru and Ecuador. We demonstrate that both eared and earless species call, although each lineage has distinct approaches to reproductive communication. We also show that earless species begin to grow middle ear structures like the columella and tympanic annulus, but this process is interrupted and differentiation of those structures does not follow the same trajectory as in eared species. Post-metamorphic regression of ear structures likely resulting from slowed development (heterochrony), which is common in bufonids, may have led to repeated ear loss and behavioral shifts in acoustic communication in toads.
