Echolocators Are Smaller Than Their Non-Echolocating Relatives: Agility Counts in Dark, Three-Dimensional Habitats

Evolutionary and behavioral adaptations are frequently linked to animal sensory perception. Echolocators have evolved instantaneous and highly adaptive control over their sensory and motor actions enabling them to detect and capture rapidly moving, evasive prey in three-dimensional space. Specifically, among volant bats, maneuverability decreases with increasing mass, while toothed whales and dolphins have evolved tight turning rates and radii to enable them to capture small and elusive fish. We thus hypothesize that selection pressures should have driven the evolution of relatively smaller body size among echolocators to enhance their agility. To test this, we conducted PGLS and GLMM model analyses comparing the body mass of 1327 echolocating species with 4878 non-echolocating species. In support of our body size filtering hypothesis, echolocating species tended to be significantly smaller than their non-echolocating relatives across the entire body mass range, both generally and at the order and family levels. Furthermore, our findings transcended the concurrent effects of habitat type and dietary preferences on modulating body size distributions, as well as ecogeographical rules relating to the evolution of body size. This shows that the echolocator-body size relationship has evolved independently across vertebrate taxa that diverged millions of years ago. Nevertheless, the resultant diversity of extant, relatively small echolocating species and the key functional roles they play in ecosystems may be vulnerable to contemporary anthropogenic disturbances.