Meeting Abstract
Eyes are often reduced or lost in species that inhabit dark environments, indicating that such habitats relax, or even reverse, selection pressure for eyes. Sand crabs (Lepidopa benedicti) change habitats during their lives, resulting in different selection pressures on the visual system during their life cycle. Sand crabs have a pelagic larval stage with typical eyes for a larval crustacean, but metamorphose into a benthic, digging adult that spends most of its life submerged under sand with small eyespots. We tested whether these adult eyespots are functional. To test for phototaxis, adult sand crabs were placed in an aquarium that was half covered and half in light. Sand crabs showed no significant preference for the light or dark side (χ2= 0.533; p = 0.465). Anatomically, the adult eyespots have no obvious facets typical of arthropod ommatidia, but are innervated by a nerve that connects to the brain. Extracellular electrophysiological recording show that the optic nerve has the ability to generate action potentials, but it is no clear yet if there are any physiological responses to light. Analyses of RNA transcriptomes are underway to determine if opsins are expressed in the anterior region of the adult sand crab. The evidence suggests that the visual system in adult sand crabs is a non-functional remnant of the larval visual system.
