INTRODUCTION

One of the central questions in zoology concerns the adaptations of sensory filtering mechanisms to species-specific environments. Echolocating bats represent ideal models in auditory neurobiology to understand the underlying principles from both phylogenetic and ontogenetic points of view. They have adapted basic mammalian features of sound transmission by external and middle ears, and of frequency analysis by the inner ear to the working range of their biosonar, which in certain species operates more than three octaves above the high frequency limit of hearing in humans. Furthermore, for matched filtering of the dominant components of their echolocation signals, certain species have evolved the most sharply tuned auditory receptor systems of the animal kingdom.

Following a brief introduction into sonar systems, the first part of this chapter describes comparative anatomical studies of the cochlea in bats. Special emphasis is devoted to an analysis of the structural variations on the common mammalian cochlear Bauplan as adaptations to ecological constraints and specialized acoustic performance. Diversity of cochlear mechanisms and the adaptive value of specialized features in cochlear morphology will be judged by a comparative analysis of 1) non-related bats who evolved Doppler-sensitive sonar systems via convergent evolution (Rhinolophus rouxi – Pteronotus parnellii), and 2) related bats that employ different types of sonar (P. parnellii – Pteronotus quadridens). The second part of the chapter addresses the question of how Doppler-sensitive sonar and specialized frequency analysis by the cochlea develops during ontogeny in horseshoe bats.