Visual Acuity and the Evolution of Signals

• Published in: Trends in ecology & evolution (Amsterdam) 2018-05, Vol.33 (5), p.358-372
• Main Authors: Caves, Eleanor M., Brandley, Nicholas C., Johnsen, Sönke
• Format: Article
• Language: English
• Subjects: eye size; patterns; perception; private communication; sensory system acuity; signal active space; visual ecology
• ISSN: 0169-5347; 1872-8383
• DOI: 10.1016/j.tree.2018.03.001

Acuity, the fineness with which sensory systems perceive and parse information, limits the information that organisms can extract from stimuli. Here, we focus on visual acuity (the ability to perceive static spatial detail) to discuss relationships between acuity and signal form and evolution. Research suggests that acuity varies by orders of magnitude across species, and that most animals have much lower acuity than humans. Thus, hypotheses regarding the function of spatial patterns must account for the acuity of relevant viewers. New data quantifying acuity in a range of taxa allow us to examine correlations between acuity and ecology, elucidate the selective forces that receiver acuity places on signal evolution, and examine how signals might appear to viewers with different acuities. Recent increased interest in visual acuity, the ability to perceive static spatial detail, has shown that acuity is highly variable, ranging over four orders of magnitude across species with image-forming eyes. Human visual acuity is some of the highest in the animal kingdom, meaning that researchers may develop hypotheses regarding the function of spatial patterns that do not account for the relevant viewer’s sensory capabilities. Signals can potentially exploit differences in visual acuity between species, which may arise due to differences in eye type, eye size, and/or viewing distance. Because acuity can vary between two viewers of the same scene, it represents a promising yet understudied channel for private communication. Small animals, particularly those with compound eyes, have low acuity and thus can only perceive fine patterns over very short distances.