Rapid evolution of the primate larynx?

Abstract

Tissue vibrations in the larynx produce most sounds that comprise vocal communication in mammals. Larynx morphology is thus predicted to be a key target for selection, particularly in species with highly developed vocal communication systems. Here, we present a novel database of digitally modeled scanned larynges from 55 different mammalian species, representing a wide range of body sizes in the primate and carnivoran orders. Using phylogenetic comparative methods, we demonstrate that the primate larynx has evolved more rapidly than the carnivoran larynx, resulting in a pattern of larger size and increased deviation from expected allometry with body size. These results imply fundamental differences between primates and carnivorans in the balance of selective forces that constrain larynx size and highlight an evolutionary flexibility in primates that may help explain why we have developed complex and diverse uses of the vocal organ for communication.

Selection on vocal output affects laryngeal morphology in rats

“…Many similar modifications for loud low‐frequency vocalizations have been documented in a range of ungulates (Frey et al, 2007; Frey et al, 2011; Frey & Hofmann, 2000; Frey & Riede, 2003). Nonhuman primates show a suite of specific vocal modifications, including many types and sizes of laryngeal air sac (Fitch, 2016; Schön Ybarra, 1995), and large‐scale comparisons of laryngeal morphology in primates and carnivores suggest that the primate larynx has evolved more rapidly than that of carnivores (Bowling et al, 2020).…”

“…This finding is clearly relevant to researchers using USVs to gain insight into the emotional state and stress response, as well as to broader questions in the evolution of communication (cf. Bowling et al, 2020; Dunn et al, 2015; Fitch, 2016).…”

“…Vocal fold length was approximated based on the mineralization patterns of the 3D reconstructions. We placed landmarks on the dorsal border of each arytenoid cartilage, and in the area of vocal fold attachment on the thyroid cartilage; we then measured the distance between the arytenoid and thyroid landmarks, resulting in two vocal fold measurements per individual (right and left; Bowling et al, 2020). We recorded the average value as “mean vocal fold length” for each individual to be used for all further statistical analysis.…”

Small carnivorans, museums and zoos

“…For example, there is a long‐term collaboration with the University of Vienna, Austria, to preserve and CT scan the larynges of a wide variety of mammals, including small carnivorans, in order to record their structure and function. This unique collection of more than 400 specimens has already been used to demonstrate that the larynges of primates have evolved faster than those of carnivorans (Bowling et al , 2020). National Museums Scotland also collaborates with Manchester Metropolitan University (UK) on the function of the baculum, which has led to a recent publication showing that this bone has evolved to increase the length of intromission in carnivorans (Brassey et al , 2018).…”

Gap junction-mediated glycinergic inhibition ensures precise temporal patterning in vocal behavior

“…Unlike motor systems controlling locomotion and respiration ( Ramirez and Baertsch, 2018 ; Grillner and El Manira, 2020 ), in-depth inquiries of cellular and network properties of brainstem neurons influencing acoustic signaling remain relatively unexplored, despite advances in characterizing the musculoskeletal periphery ( Mead et al, 2017 ; Kwong-Brown et al, 2019 ; Riede et al, 2019 ; Bowling et al, 2020 ). A neurobehavioral challenge often facing soniferous species is fine temporal control of rapid modulations of acoustic waveforms.…”