Sexual Selection in the Loud Calls of Male Primates: Signal Content and Function

Abstract

Researchers have used sexual selection theory and hypotheses based on intersexual mate choice and intrasexual mate competition to explain the role of spontaneous long-distance vocalizations emitted by adult maleprimates, relying on the tacit assumption that assessment or identity cues are encoded in the vocalizations. I review the published literature and aim to substantiate a relationship between sexual selection and long-distance vocal communication in primates. First, I review findings from nonprimate taxa to determine the relative importance of inter-and intrasexual selection and to provide a background for examining primates. Next, I describe several hypotheses for signal content and function in adult male loud calls. Then, I examine the available data across Primates for evidence to support or to refute these hypotheses and to determine if they meet proposed criteria for demonstrating sexual selection [Snowdon, C. T. (2004) . Sexual Selection in Primates: New and Comparative Perspectives]. Signal content refers to patterns of acoustic features within vocalizations from which listeners might extract cues or information about the signaler. I interpret signal function, in turn, from behavioral responses of receivers and assume it has ultimate effects on the evolution and design of acoustic signals if direct fitness consequences exist. After the general review across primates, I propose orangutans as a candidate species for further evaluation of sexual selection in vocal communication. The available evidence corroborates a demonstrable relationship between sexual selection and adult male loud calls

Masculine voices signal men's threat potential in forager and industrial societies

“…Recent research has focused on the evolutionary reasons for the pubertal development of vocal sex differences in humans [11] and non-human primates [12]. Of particular interest has been sexual selection, which operates through both mate choice, favouring ornaments and sexual displays for attracting mates, and contest competition, favouring size, strength, aggression, weapons and threat displays [13].…”

Sexual selection on male vocal fundamental frequency in humans and other anthropoids

“…Some have suggested that male vocalizations evolve to intimidate male competitors and/or attract mates [6,13]. For example, among orang-utans, lower-ranking males avoid long calls given by higher-ranking males [14], suggesting that acoustic cues convey threat potential to conspecifics.…”

“…More generally, scant evidence exists to support a role for sexual selection in shaping F 0 and other vocal sexual dimorphisms across primates [6], and there are plausible alternative hypotheses: F 0 dimorphism may represent a byproduct of selection for greater male size or long-distance transmission of male calls [36], or reflect selection for sex identification. The latter two hypotheses predict relationships between habitat and F 0 dimorphism.…”

Sexual selection and the loss of laryngeal air sacs during the evolution of speech

“…Species with greater levels of precopulatory male-male competition and reduced levels of sperm competition have been shown to possess adaptations that enable them to produce exaggerated calls, suggesting that sexual selection plays a critical role in regulating vocal communication (Delgado, 2006;Charlton and Reby, 2016). Given this, air sacs are likely to be more common, and perhaps larger, in species under strong sexual selection.…”