Glander, K. E. | bioRxiv Science

bioRxiv2019

Audiograms of howling monkeys: are extreme loud calls the result of runaway selection?

The eponymous vocalizations of howling monkeys (genus Alouatta) are associated with territorial defense and male-male competition, yet the extreme loudness of howls, which are among the loudest vocalizations of any terrestrial mammal, have yet to be fully explained. Loudness facilitates long-distance sound propagation but the effectiveness of any vocal signal depends in part on the auditory capabilities of the intended receiver, and the auditory sensitivities of howling monkeys are unknown. To better understand the evolution of loud calls, we used the auditory brainstem response (ABR) method to estimate the auditory sensitivities of Alouatta palliata. The mean estimated audiogram of four wild-caught adults displayed a w-shaped pattern with two regions of enhanced sensitivity centered at 0.7-1.0 and 11.3 kHz. The lower-frequency region of auditory sensitivity is pitched moderately higher than the fundamental frequencies of howling, whereas the higher-frequency region corresponds well with harmonics in an infant distress call, the wrah-ha. Fitness advantages from detecting infants amid low-frequency background noise, including howling, could explain the incongruity between our ABR thresholds and the fundamental frequencies of howling. Attending to infant calls is expected to enhance reproductive success within an infanticidal genus, and we suggest that the extraordinary loudness of male howling is an indirect (runaway) result of positive feedback between the selective pressures of hearing infant distress calls and deterring infanticide.

animal behavior and cognition↗

bioRxiv2017

Associations Between Nutrition, Gut Microbiome, and Health in A Novel Nonhuman Primate Model

Red-shanked doucs (Pygathrix nemaeus) are endangered, foregut-fermenting colobine primates which are difficult to maintain in captivity. There are critical gaps in our understanding of their natural dietary habits including consumption of leaves, unripe fruit, flowers, seeds, and other plant parts. There is also a lack of understanding of enteric adaptations, including their unique microflora. To address these knowledge gaps, we used the douc as a model to study relationships between gastrointestinal microbial community structure, diet, and health. We analyzed published fecal samples as well as detailed dietary history from doucs with four distinct lifestyles (wild, semi-wild, semi-captive, and captive) and determined gastrointestinal bacterial microbiome composition using 16S rRNA sequencing. A clear gradient of microbiome composition was revealed along an axis of natural lifestyle disruption, including significant associations with diet, health, biodiversity, and microbial function. We identified potential microbial biomarkers of douc dysbiosis, including Bacteroides and Prevotella. Our results suggest a gradient-like shift in captivity causes an attendant shift to severe gut dysbiosis, thereby resulting in gastrointestinal issues.

microbiology↗