The relationship between testosterone and long-distance calling in wild male chimpanzees

Abstract

Long-distance calling is a common behaviour in animals that has various important social functions. At a physiological level, calling is often mediated by gonadal hormones such as testosterone (T), particularly when its function is linked to intra-sexual competition for mates or territory. T also plays an important role in the development of vocal characteristics associated with dominance in humans. However, the few available studies of T and vocal behaviour in non-human primates suggest that in primates T has less influence on call production than in other animals. We tested this hypothesis by studying the relationship between T concentrations and pant hooting in wild male chimpanzees (Pan troglodytes schweinfurthii) of the Kanyawara community in the Kibale National Park, Uganda. We found three kinds of correlation. Hourly T averages were positively associated with hourly rates of pant-hooting. Monthly T levels were likewise correlated with monthly rates of pant hooting after controlling for other influences such as fission-fusion rates. Finally, males with high T levels had higher peak frequency at the start of the call climax. These results suggest that T affects the production of pant-hoots in chimpanzees. This implies that the pant-hoot call plays a role in male-male competition. We propose that even in cognitively sophisticated species, endocrine mechanisms can contribute to regulating vocal production.

Sequential information in a great ape utterance

“…Our results are consistent with earlier analyses showing that social status is one of the functions of pant hooting4555, and that a caller’s social standing is mainly reflected in the call’s loud climax3940. We found relatively strong modality and phase specificities for ‘social status’, which supports this notion.…”

“…We found relatively strong modality and phase specificities for ‘social status’, which supports this notion. Indeed, as mentioned before, some of the acoustic properties of a pant hoot climax, such as its initial peak frequency, correlate with testosterone40, a hormone that in many animals mediates the production of calls involved in intra-sex competition565758, and, in chimpanzees, reflects social status and potentially male quality5960.…”

“…Chimpanzee pant hoots have been the target of much field research, but the focus has usually been on the climax part of the call, which is individually distinctive and can be linked to a caller’s social status3940, facilitating individual recognition over long distances in a society with a high degree of fission-fusion dynamics4142434445. There have also been suggestions that the acoustic quality of the climax differs between calls produced in travelling and feeding contexts, but the corresponding data are inconclusive4647.…”

“…Acoustic analyses of primate vocalisations are traditionally carried out by manually extracting a limited number of arbitrarily chosen acoustic parameters from spectrograms, a time-consuming and tedious process that is based on arbitrarily selecting variables for subsequent statistical analyses4042. In all likelihood, however, the neural machinery devoted to processing vocal sounds does not usually deal with single acoustic parameters.…”

Testosterone and reproductive effort in male primates

“…Similarly, the rate of long-distance calling in wild male black howler monkeys was not affected by testosterone production (Rangel-Negrín et al 2011). In male chimpanzees, however, mean monthly testosterone levels correlated with mean monthly rates of pant-hooting, and diurnal patterns of pant-hooting paralleled those of testosterone production (Fedurek et al 2016). Comparable data are not available from orangutans, but in that species loud calls are only produced by dominant, flanged males (Mitani 1985), who maintain higher androgen levels than unflanged males (Marty et al 2015).…”