Meeting Abstract
Here we integrated genetic, morphological, physiological, and developmental data to propose potential selection pressures contributing to convergent loss and potential regain of middle ear structures across the family of true toads (Bufonidae). Middle ear structures are shared by most tetrapods for hearing airborne sound, yet they have been lost at least eleven times in Bufonidae, despite the fact that frogs and toads are known to use acoustic communication for mate attraction and other conspecific interactions. Sequence analysis of coding regions in 60 bufonid species (16 earless, 44 eared) nominates six of 30 candidate genes known to be important for tetrapod middle ear development as possible contributors to middle ear loss. These six candidate genes exhibited relaxed purifying selection in earless lineages when compared to closely-related eared lineages. Earless lineages did not share any parallel amino acid changes or evidence for positive selection within coding regions associated with tetrapod middle ear development, complementing our lack of evidence for shared selection pressures acting on anuran middle ear loss in relation to ecology or pleiotropic skull trade-offs. The relaxed purifying selection associated with anuran middle ear loss provides an intriguing starting point for the investigating the genetic basis of anuran middle ear development in relation to better-known tetrapod groups. With this added genetic evidence, we further support the hypothesis that middle ears are lost by a combination of relaxed selection on the middle ear and changes in development rate.
