Laboratory culture of the California Sea Firefly Vargula tsujii (Ostracoda: Cypridinidae): Developing a model system for the evolution of marine bioluminescence

Bioluminescence, or the production of light by living organisms via chemical reaction, is widespread across Metazoa. Culturing bioluminescent organisms from diverse taxonomic groups is important for determining the biosynthetic pathways of bioluminescent substrates, which may lead to new tools for biotechnology and biomedicine. Although some previously cultured luminescent groups represent independent origins of bioluminescence, cnidarians, ctenophores, and brittle stars use luminescent substrates (luciferins) obtained from their diets, and therefore are not informative for determination of the biosynthethic pathways of the luciferins. Terrestrial fireflies do synthesize their own luciferin, but the biosynthetic pathway for firefly luciferin remains unclear. An additional independent origin of endogenous bioluminescence is found within ostracods from the family Cypridinidae, which use their luminescence for defense and, in Caribbean species, for courtship displays. Here, we report the first complete life cycle of a luminous ostracod (Vargula tsujii, the California Sea Firefly) in the laboratory. We also describe the embryonic development of Vargula tsujii and discuss the size classes of instar development. We find embryogenesis in V. tsujii ranges between 25-38 days, and this species appears to have five instar stages, consistent with ontogeny in other cypridinid lineages. We estimate a complete life cycle at 3-4 months. We present the first complete mitochondrial genome for Vargula tsujii. Finally, we find no evidence of significant population genetic structure or cryptic species throughout the southern California range of V. tsujii. Bringing a luminous ostracod into laboratory culture sets the stage for many potential avenues of study, including the biosynthetic pathway of cypridinid luciferin and genomic manipulation of an autogenic bioluminescent system.