Visual and cognitive abilities of non-marine ostracods in a colorful world

Miniaturized analytical systems are an emerging technology with several applications in aquatic ecology, including assessing the cognitive abilities of invertebrates through their sensory systems (ROMANO et al., 2022). Such systems prove to be particularly suitable for the non-invasive study of the relationship between photoreception and learning in non-marine ostracods. Ostracods are bivalve crustaceans whose living non-marine representatives belong to the order Podocopida (Ostracoda) (SMITH et al., 2015; MEISCH et al., 2019). Podocopid ostracods have a simple optic system consisting of three eye cups, known as the naupliar eye, composed of specialized cells and a lensmirror optic apparatus (ELOFSSON, 2006). In some species, a transparent area of the calcitic carapace serves as an additional lens (ANDERSSON & NILSSON, 1981; TANAKA, 2005, 2006). Variations in optic system composition, size, and other morphological and ecological characteristics exist among species (MEISCH, 2000). Molecular studies suggest that species in the genus Heterocypris synthesize wavelength-sensitive photopigments (HENZE & OAKLEY, 2015; PALECANDA et al., 2022). ROMANO et al. (2022) demonstrated that miniaturized arenas are appropriate for analyzing behavioral aspects in non-marine ostracods, specifically showing that Heterocypris incongruens (Ramdohr, 1808) is able to perform associative learning with light stimuli of different wavelengths. We extended the investigation of photoreception-related ethological behaviors to several species of non-marine ostracods. Using two custom-designed miniaturized arenas, we assessed photoreceptive abilities and learning ability by computational analysis of the trajectories and movement of individuals subjected to different light stimuli in the visible range. We compared responses to colored light stimuli and conditioning and conducted experiments on spatial memoconditioning sessions, and their ability to discriminate previously light-associated stimuli was tested against unconditioned individuals. The ostracod species examined showed different responses, possibly reflecting diverse adaptations to specific ecological requirements. Our results contribute valuable insights into the adaptive mechanisms underlying the sensorial and cognitive functions in non-marine ostracods. Furthermore, this approach is promising for broader applications in elucidating the behavioral and ecological dynamics of these organisms, thereby enhancing our comprehension of their roles in aquatic ecosystems.