PhD - ECR City University of Hong Kong Hong Kong, Hong Kong
Abstract Body : Bats constitute more than 20 percent of mammalian species and exhibit significant morphological, behavioural, and ecological diversity. Their capacity for flight and echolocation have enabled bats to advance into various environments, thus leading to their remarkable evolutionary success. However, the origin and evolution of laryngeal echolocation remain subjects of debate, with conflicting hypotheses proposing either a single origin or multiple independent origins. The larynx, responsible for sound production, remains poorly understood in terms of its anatomy and the variations associated with echolocation strategies. Also, certain bat families possess cartilaginous tracheal chambers located posteriorly to the cricoid cartilage, but their role in vocal production, as well as their distribution among different bat clades, remains insufficiently characterized.
In order to elucidate the relationship between echolocation behaviour and laryngeal anatomy in bats, we examined the larynges of 22 bat species from five families high-resolution iodine contrast-enhanced X-ray microtomography. Additionally, we included six mammalian outgroup species for comparison. We compared the laryngeal forms through detailed morphological observations and measurements. Furthermore, we explored the evolutionary history of the bat larynx, employing phylogenetic comparative methods.
Contrary to previous assumptions, our findings revealed that laryngeal muscle hypertrophy is not a universal characteristic among bats and exhibits variable degrees of development. Morphologically, the larynges of Pteropodidae were comparable to those of non-bat mammals. Within laryngeal echolocating bats, we identified two distinct morphotypes, illustrating clear differences between Rhinolophoidea and Yangochiroptera. These differences primarily involve the volume of the cricothyroid muscle and the shape of the cricoid and thyroid cartilages. The tracheal chambers also exhibit variations in size and topology across bat families, with ventral placement observed in Yangochiroptera and dorsal placement in Rhinolophoidea.
The observed diversity in laryngeal forms, distributed along the bat phylogeny, likely reflects adaptations to different echolocation strategies. The similarity of laryngeal morphology among Pteropodidae and outgroup mammals suggests that ancestral traits are retained and shared from the common ancestor of all bats to the common ancestor of Yinpterochiroptera and later the Pteropodidae. Consequently, the derived laryngeal forms observed in Rhinolophoidea and Yangochiroptera, as well as the topology of tracheal chambers, may have evolved independently.
