The emergence of blinking is linked to the shift from water to land in vertebrate history, a topic explored through modern fish that live at the edge of both worlds. In coastal habitats, the mudskipper thrives by keeping its body moist while surviving in a semi-terrestrial niche. Its eyes are perched high on the head, offering a wide field of view when the body is partially exposed to air. When the mudskipper blinks, the eye retraction mechanism briefly withdraws the globe into the socket and is covered by a specialized skin layer. This action, which resembles a human blink in duration, serves multiple essential roles for an animal that spends much of its time out of water. High-speed video analyses show that mudskippers perform this blink in a rapid sequence, helping to refresh the surface of the eye and protect it from irritants encountered in mud and sand. The study of these behaviors compares mudskippers with a closely related species that does not exhibit the same blinking pattern, highlighting the distinct anatomical and behavioral adaptations that accompany terrestrial living.
Eye anatomy in mudskippers features a dorsal placement of the eyes, a design that supports both underwater and aerial perspectives. When a blink occurs, the eye is momentarily retracted into the socket and covered by an elastic skin cap that seals the surface. The duration of a blink aligns closely with a typical human blink, suggesting a rapid, efficient process honed by natural selection to maintain clear vision in a challenging environment. Researchers observed that blinking arises from a reorganization of existing muscles that altered their movement direction, alongside the development of a previously unseen tissue known as the dermal calyx. This combination allows the mudskipper to restore moisture and remove debris in a setting where dry air and suspended particles can threaten ocular health.
A striking feature is the absence of lacrimal glands in mudskippers. Instead, eye moisture is sustained by the moist mucus that lines the body surface, which in turn bathes the eye. This strategy illustrates how terrestrial adaptation can drive physiological changes that reduce reliance on structures found in fully aquatic relatives. The act of blinking also appears to serve a protective function, clearing debris from the eyeball and cushioning it from potential damage that arises when the animal navigates through mud, sand, and water-exposed habitats. Such insights come from careful observation of eye movements, anatomical dissections, and comparisons with related taxa that show little or no blinking. This body of work suggests that adapting to life on land may inherently promote eye-soothing strategies that stay effective even when the environment becomes dry and dusty.
Overall, the evidence points to blinking as an adaptive response to terrestrial challenges rather than a random trait. As mudskippers turned their lifestyle toward land, the reorganization of muscles and the creation of the dermal calyx combined to improve eye health, moisture retention, and debris clearance. This convergence between structure and behavior underscores a broader principle: the move to dry habitats often brings about coordinated changes in both form and function that support more complex visual demands. The findings contribute to a growing understanding of how ancient vertebrates might have managed ocular protection and hydration during transitions away from fully aquatic life.