Allometric scaling of a superposition eye optimises sensitivity and acuity in large and small hawkmoths

Abstract

Animals vary widely in body size across and within species. This has consequences in large and small individuals for the function of organs and body parts. How these scale in relation to body size reveals evolutionary investment strategies, often resulting in trade-offs between functions. Eyes exemplify these trade-offs, as they are limited by their absolute size in two key performance features: sensitivity and spatial acuity. Previous studies of the 3D structure of apposition compound eyes, which are ideal models for allometric studies due to their size polymorphism, revealed that allometric scaling improves both local resolution and visual sensitivity in larger bumblebees (Taylor et al., 2019). Here, we build on the established methods and results to investigate allometric scaling in superposition compound eyes - the second prominent eye type in insects - for the first time. Our research highlights a surprising strategy to cope with the challenge of trading off sensitivity and spatial resolution in small eyes, as we show that the eyes of the hummingbird hawkmoth retain an optimal balance of these performance measures across all body sizes.