The vocal apparatus of bats: an understudied tool to reconstruct the evolutionary history of echolocation?

Abstract

Until recently, bat phylogeny separated megabats (laryngeally non-echolocators) and microbats (all laryngeal echolocators) into two distinct clades. This segregation was consistent with the assumption that laryngeal echolocation was acquired by a common ancestor and inherited by all microchiropterans. Thus, laryngeal echolocation was regarded to have evolved once. Recent advances in bat genome sequencing have added insights regarding the origin of bats and their phylogenetic relationships. The megabats previously thought to be phylogenetically isolated are now sharing a common ancestor with the superfamily Rhinolophoidea, which is constituted of laryngeal echolocators. This new relationship brings a counterpoint regarding the hypothesis of single origin of echolocation, which could have appeared several times independently. Concomitantly, recent studies in bat evolutionary developmental biology have illuminated the importance of characters from embryonic development to discussions of how and when echolocation evolved. Here, we describe how comparative chiropteran laryngeal morphology is a novel area of research that could improve the understanding of echolocation and may help resolve the evolutionary history of bats. This review provides morphological descriptions and comparisons of the larynx, bioacoustics interpretations, and newly developed visualisation approaches (i.e., contrast-enhanced computed tomography). We discuss the importance of understanding (1) laryngeal sound production so it may be linked with the evolution of the Chiropteran auditory system and (2) the evolution of laryngeal morphology to understand the ecological and behavioural aspects of bat biology.