Growing eyes on growing shells reveal how chitons scale vision.

Area of Science:

• Marine Biology
• Evolutionary Biology
• Sensory Ecology

Background:

• Distributed visual systems are often assumed to have uniform photoreceptive units.
• Chitons possess a complex array of shell eyes embedded in their dorsal shell plates, with continuous eye addition throughout life.

Purpose of the Study:

• To investigate the relationship between lens volume and position in chiton shell eyes.
• To determine if chiton eyes are formed at consistent sizes during ontogeny.
• To understand the implications of eye size variation for visual system function.

Main Methods:

• Synchrotron microcomputed tomography (microCT) was used to reconstruct shell-eye lenses in six chiton specimens across five species.
• Statistical analysis, including log-transformed mixed-effects models, was employed to assess scaling patterns and the influence of body size.

Main Results:

• Significant changes in eye size were observed along the growth axis, with lens volume increasing allometrically towards the shell margins.
• Lens diameter could more than double from the oldest to the youngest eye within an individual.
• Growth trajectories and scaling patterns in eye size differed among chiton species.

Conclusions:

• Chiton visual systems exhibit a broad range of eye sizes within individuals, challenging the assumption of homogeneity in distributed arrays.
• Ontogenetic changes in eye size lead to substantial differences in visual sensitivity.
• The observed size gradient has significant implications for visual function, redundancy, and information integration in chiton shells.