image: Ornstein-Uhlenbeck model results. (A) Phylogenetic tree and residuals from a pGLS regression of larynx size to log body-length. Carnivorans (red) exhibited smaller larynges than expected based on body size, whereas primates (blue) exhibited larger larynges. Among primates, atelids exhibited exceptionally large larynges (upper set of dashed lines), and papionines exhibited exceptionally small larynges (lower dashed lines). Arrows indicate where grade shifts in mean larynx size are estimated to have arisen; percentages indicate support for these estimations from a bootstrap analysis (see Methods). (B) Computer larynx models derived from CT scans depicted in situ for two species with comparable body lengths (71.4 cm for the red fox and 68.5 cm for the siamang), showing the larger relative size of the primate larynx. The data used to create this figure are located in S1 Data, sheet B, columns B and C. CT, computed tomography; pGLS, phylogenetic generalized least squares. view more
Credit: Bowling et al, 2020
The larynx is larger, more variable in size, and has undergone faster rates of evolution in primates than in carnivores, according to a study published August 11, 2020 in the open-access journal PLOS Biology by Daniel Bowling of Stanford University, W. Tecumseh Fitch of the University of Vienna, and colleagues.
The larynx is the main organ of vocal production, and a key target for evolutionary selection, particularly in those species that have a highly developed vocal communication systems. To shed light on the evolution of the larynx, Bowling and Fitch combined 3D computer models built from X-ray computed tomography scans with detailed digital measurements. They used these techniques to compare the larynx structure of 55 different mammalian species, representing a wide range of body sizes among primates and carnivores (from pygmy marmoset to gorilla and from dwarf mongoose to tiger). Carnivores were chosen as a comparable order of mammals with a similarly wide size range.
Using comparative methods known as phylogenetics, they showed that the larynx has evolved more rapidly in primates than in carnivores, resulting in a pattern of larger larynx size relative to body size, and greater variability in size. Acoustic vocalization data suggest that these differences are relevant to vocal communication. Moreover, larynx size is less tightly coupled to body size in primates than it is in carnivores, suggesting that the primate larynx has been freer to respond to fluctuations in evolutionary pressure. Taken together, the results imply fundamental differences between primates and carnivores in the balance of evolutionary 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.
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Research Article
Peer reviewed; Experimental study; Animals
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Citation: Bowling DL, Dunn JC, Smaers JB, Garcia M, Sato A, Hantke G, et al. (2020) Rapid evolution of the primate larynx? PLoS Biol 18(8): e3000764. https://doi.org/10.1371/journal.pbio.3000764
Funding: This work was funded in part by Austrian Science Fund (FWF) DK Grant "Cognition & Communication" (#W1262-B29). DLB was supported by a Lise Meitner grant from the FWF (#M1773-B24). JCD was supported by a grant from the Royal Society (RSG\R1\180340) and the Rhinology and Laryngology Research Fund. National Museums Scotland thanks the Negaunee Foundation for their generous support of a preparator who dissected the larynges use in the study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Journal
PLoS Biology