Meeting Abstract
Vertebrate eyes, even with differences due to ecology, (generally) scale hypometrically with body size – as a result of a relationship called Haller’s Law. Isometric eye size scaling is, however, predicted for faster-moving animals, in a relationship known as Leuckart’s Law. Increased eye size within this context is often interpreted or assumed to be a proxy for higher visual acuity or resolution. Although the axial length of the eye does correlate with visual acuity, studies of birds and mammals conflict in supporting the eye-size-to-velocity relationship, in that it is currently unclear whether faster locomoting animals require higher visual resolution, or if variability in eye size is primarily explained by overall body size. I analyzed data on visual acuity, linear dimensions of the eye, maximum linear velocity, body length, and mass for multiple orders of running and flying insects, mammals, and birds to broadly evaluate the resolution-to-speed relationship. Whereas eye size and velocity do both scale with body-size variables, neither eye size nor acuity scale with speed in any phylogenetic group or locomotor type. Additionally, neither acuity nor eye size matches the empirically observed ‘U’-shaped curvilinear relationship between animal body size and speed. This study does not support Leuckart’s Law, and I suggest that high visual resolution is not necessarily required for high-speed locomotion.
