Stockholm University Researchers Uncover Why Evolutionary 'Eyespots' Appear In Specific Ray Species

Stockholm University researchers find that eyespots in rays and skates serve as a defensive trade-off for species lacking venom or electric organs.

By: AXL Media

Published: Apr 24, 2026, 6:53 AM EDT

Source: Information for this report was sourced from EurekAlert!

The Evolutionary Logic of Visual Deterrence in Marine Life

Bold circular patterns known as eyespots are not merely random decorative features but are calculated components of a species' defensive toolkit. According to lead author Madicken Åkerman of Stockholm University, eyespots evolve only under specific ecological conditions as a solution in the ongoing arms race between predator and prey. By examining more than 90% of all known skates and rays, the research team determined that visual signals serve as a secondary line of defense when an animal lacks more robust physical or electrical deterrents.

The Defensive Trade-Off Between Weapons and Markings

Marine species face constant threats from sharks and marine mammals, leading to the development of diverse survival strategies. According to the study, species equipped with venomous tail spines or the ability to deliver electric shocks rarely develop conspicuous markings. Conversely, smaller-bodied species without these biological weapons are significantly more likely to evolve bold spots or eyespots. This suggests that if an animal is already mechanically or electrically "armed," the metabolic and survival cost of maintaining a visual warning signal is unnecessary.

Environmental Influences and Light Penetration in Deep Waters

The effectiveness of a visual signal is entirely dependent on the environment in which the species resides. According to senior author John Fitzpatrick, eyespots are most effective in bright, shallow waters at depths of less than 200 meters. In deep-sea environments where light is scarce, these markings often disappear because the benefit of being seen by a predator as a warning no longer outweighs the risk of being easily spotted. This environmental pressure ensures that conspicuous markings are frequently lost as species migrate to darker habitats.