The evolution of eyespots in skates and rays

Area of Science:

• Evolutionary biology
• Marine biology
• Animal behavior

Background:

• Animals utilize diverse anti-predator adaptations, forming 'defence portfolios'.
• The evolutionary pathways and co-occurrence patterns of these defenses remain largely unexplored.
• Understanding these patterns is crucial for explaining the distribution of specific adaptations.

Purpose of the Study:

• To investigate the evolution of conspicuous visual markings alongside other anti-predator defenses in skates and rays (Batoidea).
• To determine the factors influencing the co-evolution and mutual exclusivity of different defense strategies.
• To explain the presence or absence of iconic defenses like eyespots in various species.

Main Methods:

• Phylogenetic analysis of 580 skate and ray species.
• Compilation of data on conspicuous markings (e.g., eyespots), mechanical (venomous stings), and electrical defenses.
• Inclusion of adult body size and habitat depth as ecological variables.

Main Results:

• Eyespots evolve stepwise from other conspicuous markings.
• Evolutionary increases in multiple markings are often followed by reductions.
• Robust defenses and eyespots show alternative evolutionary trajectories; eyespots are favored in smaller, less defended species in well-lit habitats.

Conclusions:

• Defense strategies are not randomly combined, indicating alternative evolutionary pathways.
• The presence of robust defenses constrains the evolution of eyespots.
• Ecological factors like light availability and body size significantly influence the evolution of anti-predator visual signals.