Evidence of visual learning and wavelength differential responses in three podocopids (Crustacea: Ostracoda)

Ostracods are small bivalved crustaceans that inhabit a wide range of aquatic environments, from fully marine to brackish and freshwater systems. All non-marine species belong to the order Podocopida. The sensory biology and behavioral capacities of ostracods remain poorly understood, even though these traits play pivotal roles in habitat exploration, food searching, mate recognition, and predator avoidance. In particular, studies addressing vision and learning ability are still scarce. Although visual structures in ostracods are often reduced or simplified, they exhibit considerable variation across taxa. In this study, we investigated the photoreceptive capabilities of three podocopid species, Vizcainocypria viator, Loxoconcha elliptica, and Xestoleberis nitida, representing different families. Using miniaturized, three-chamber lab-on-a-chip arenas, we examined both innate and experience-dependent light-guided behaviors, testing whether differential wavelength sensitivity and learned associations are present, if these traits are species-specific, and which locomotory responses are associated with them.

Our results provide evidence for a simple form of long-term associative memory in ostracods, together with species-specific responses to conditioning type, light wavelength, and possibly light intensity. These responses were not restricted to spatial preferences among arena chambers, but also affected locomotory behavior.

These findings highlight ostracods as valuable model organisms for studying fundamental biological processes such as sensory integration, behavioral plasticity, and learning. More broadly, this research advances our understanding of sensory evolution in crustaceans and sheds new light on the behavioral complexity of small aquatic invertebrates.