Illuminating the impact of diel vertical migration on visual gene expression in deep-sea shrimp

Diel vertical migration (DVM) of marine animals represents one of the
largest migrations on our planet. Migrating fauna are subjected to a
variety of light fields and environmental conditions that can have notable
impacts on sensory mechanisms, including an organism’s visual
capabilities. Among deep-sea migrators are oplophorid shrimp, that
vertically migrate hundreds of meters to feed in shallow waters at night.
These species also have bioluminescent light organs that emit light during
migrations to aid in camouflage. The organs have recently been shown to
contain visual proteins (opsins) and genes that infer light sensitivity.
Knowledge regarding the impacts of vertical migratory behavior, and
fluctuating environmental conditions, on sensory system evolution is
unknown. In this study, the oplophorid Systellaspis debilis was either
collected during the day from deep waters or at night from relatively
shallow waters to ensure sampling across the vertical distributional
range. De novo transcriptomes of light sensitive tissues
(eyes/photophores) from the Day/Night specimens were sequenced and
analyzed to characterize opsin diversity and visual/light interaction
genes. Gene expression analyses were also conducted to quantify expression
differences associated with DVM. Our results revealed an expanded opsin
repertoire among the shrimp and differential opsin expression that may be
linked to spectral tuning during the migratory process. This study sheds
light on the sensory systems of a bioluminescent invertebrate and provides
additional evidence for extraocular light sensitivity. Our findings
further suggest opsin coexpression and subsequent fluctuations in opsin
expression may play an important role in diversifying the visual responses
of vertical migrators.