The evolution of hearing in Malagasy-South Asian Cichlids
Within the teleosts, we have shown that specialized morphologies have arisen at least a dozen times independently (Braun and Grande 2008). Each of these instances is a natural experiment in the evolution of hearing, allowing us to ask the following questions: Why did those species evolve high performance hearing? What ecologies are correlated with advanced hearing? How do specialized morphologies improve hearing performance and in what specific ways?
We have pursued this question most actively by examining the cichlids of Madagascar and South Asia. These sub-families (Etroplinae and Ptychochrominae) are endemic to Madagascar and southern India and Sri Lanka. Each species is narrowly endemic to a particular ectotype, ranging from shallow lakes to fast moving rapids. Through our work and earlier work by collaborator John Sparks, we have produced a species level phylogeny and are currently collecting ecological data on type localities. We are using advanced anatomical techniques (MRI and CT-Scans) to reconstruct the morphology of the inner ear, neurocranium, and pressure-transducing specializations of the gas bladder. We also use evoked potential physiology to describe the hearing enhancements of each of the specific morphologies seen in Malagasy species.