Reduced geographic variation in roars in different habitats rejects the acoustic adaptation hypothesis in the black‐and‐gold howler monkey ( Alouatta caraya )

HOLZMANN I; ARETA JI

ETHOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2019 vol. 126 p. 76 - 87

0179-1613

Vocalizations used for long‐range communication must disperse without significantstructural changes to be decoded by receivers. The acoustic adaptation hypothesis(AAH) holds that, since acoustic signals are influenced by the habitat in which theydisperse, sounds will possess specific structural characteristics to diminish sounddegradation. Additionally, vocalizations can also be influenced by genetics, anatomy,and/or cultural aspects. Here, we tested the AAH through quantitative comparisonsof roars in four allopatric populations of the black‐and‐gold howler monkey (Alouattacaraya) across an environmental gradient from open to closed, in northeasternArgentina. At each site, we obtained good‐quality recordings from three adult males,also between July and November 2013, conducted vegetation surveys (measuringtree density, canopy closure, and vertical structure), evaluated potential masking ofroars by gathering environmental sound samples, and assessed sound attenuationof a synthetic tone at three different distances: 10 m (landmark reference distance),50, and 100 m. We also tested the alternative hypothesis that acoustic propertiesof roars could be explained by population genetic divergence. Our results did notsupport the AAH. Although our four study sites were significantly different in vegetationstructure, conforming to an open‐to‐closed gradient, roars of A. caraya werenot different among populations. Likewise, although environmental sound differedbetween sites, we found no evidence of environmental sound affecting the acousticproperties of roars. The attenuation of the synthetic tone was only near significantat 100 m distance between both extreme sites from the environmental gradient. Thefour A. caraya study populations grouped into three genetically differentiated clusters.Since roar features were independent from population genetic clustering, wereject the genetic hypothesis too. The combination of high amplitude and low peakfrequency of roars, coupled to small home range size and extensive overlap betweenneighboring groups, allows roars to keep their communication value across habitatswithout need of specific environmental tuning.