The allometry of echolocation call frequencies in horseshoe bats: nasal capsule and pinna size are the better predictors than forearm length

Abstract

AbstractThe evolution of acoustic signals and the morphological traits mediating its production and reception are often coupled. The echolocation call frequencies of horseshoe bats normally decline as body size increases, but remarkable exceptions to the rule have been observed, such as Rhinolophus macrotis, R. marshalli and R. rex, having lower echolocation call frequencies than expected for their body size. Forearm length is commonly used to scale allometric relationships across horseshoe bats. However, little is known about the allometric relationships between echolocation call frequencies and morphological traits mediating directly echolocation calls' production or reception, such as the nasal capsule, the cochlea or the pinna. Here we have tested the allometry hypothesis regarding the evolution of echolocation in 12 horseshoe bats distributed in China by integrating echolocation call frequencies, phylogeny, forearm length, cochlea size, pinna size and nasal capsule size. Our results showed no significant correlation between echolocation call frequency and forearm length across these species without considering the phylogeny of the group. However, ear length, ear width and nasal capsule size were significantly and negatively correlated with echolocation call frequencies among the studied species. The fit between the linear regression model and the data was much better for the relationships between echolocation call frequencies and pinna or nasal capsule size than for the relationship between echolocation call frequencies and forearm length. These findings illustrated that both pinna and nasal capsule size were better predictors of echolocation call frequencies than forearm length. Given that the echolocation call frequencies of horseshoe bats can play key roles in sexual selection and speciation, the divergence we observed among species may influence the evolution of echolocation calls across horseshoe bats in China.