Researchers have now shown that many male animals produce vocalizations that exaggerate their size. Some species have evolved physical traits that allow them to sound much larger than they actually are, attracting mates and scaring off rivals. The details are in a paper that was just published in the journal Nature Communications.
Generally, larger animals are able to produce deeper, low-frequency calls. Some species, however, have adaptations that allow them to produce vocalizations that are abnormally low-pitched for their size. Lions and other large cats, for example, have fleshy vocal pads that allow them to produce deep roars. Koalas and some bat species are capable of vocalizing in a way that exaggerates their body size due to similar anatomical traits. The general consensus is that these adaptations help males find mates and intimidate sexual rivals. Until recently, there had never been a large-scale study designed to test the theory.
A team of researchers from the University College Dublin and the University of Sussex analyzed the male vocalizations of 72 land mammal species. They compared the sound frequencies of the calls to actual body sizes and the rate of sperm competition. The team also considered sexual size dimorphism, the difference in body size between the two sexes of a species.
The researchers found that males were more likely to use exaggerated calls when they faced high rates of sperm competition. Vocalization adaptations were generally found in species where males face fierce competition for females. In other words, the evolution of these traits was driven by sexual selection and not simply sexual size dimorphism or other factors.
The new study shows that sexual selection and competition for mates drives the evolution of traits that allow males to produce deeper calls. By exaggerating their body size, males can attract females and potentially scare sexual rivals. The authors emphasize the importance of comparative approaches when studying evolution, including when researching the development of the human voice.
Benjamin D. Charlton et al. The evolution of acoustic size exaggeration in terrestrial mammals. Nature Communications (2016).