Light-Regulated Reproduction of Ctenophores

Abstract

1. Light-regulated spawning in Ctenophore Light is one of the most common environmental factors affecting animal behaviors and life cycles. Ctenophora, as one of the earliest branched lineages among metazoans1, can provide insight on how light-regulated behaviors have evolved in animals. Mnemiopsis leidyi, an Atlantic coast ctenophore, requires 3-4 hours of darkness to spawn2. Bolinopsis microptera and Pleurobrachia bachei suggest they need to be exposed under bright light. This requirement is opposite of M.leidyi, despite B.infudibulum is phylogenetically closely related to M.leidyi. However, there is no experiment that clearly determines whether the spawning happens in a dark environment or light environment3. Furthermore, it is not clear whether it’s the dark to light transition or only the light cue triggers the spawning. I hypothesize that strong light triggers spawning in Bolinopsis, Pleurobrachia, and another species Beroe abyssicola regardless of day-night cycle. I conducted preliminary experiments on B.microptera and P.bachei. They were collected after sunset (B.microptera n = 9, N = 18, P.bachei n = 5, N= 10) and before sunset (B.microptera n = 4, N = 8, P.bachei n = 4, N= 8). The number of animals in each group changes due to availability at the FHL dock.The experiment group was exposed to headlight for 12 hours, and the control group was kept under cover of tin foil in darkness for 12 hours. There is no B.abyssicola around the dock now, so all the animals used (n=2, N=4) come from kreisel maintained by Dr. Eric Edsinger. Each group was put under light for 2 hours. The results show that all B.microptera and P.bachei collected after sunset spawned under light and did not spawn in dark. B.microptera and P.bachei collected after sunset spawned in both groups. No Beroe spawned. The results indicate that light activation of spawning seems to not be associated with phylogenetic relationship, and gradual transition from light to dark is needed for dark inhibition of spawning. 2.Ctenophore imaging methods I developed a protocol to stain ctenophores for microCT scanning collaborating with Dr.Rebecca Varney and Jorge Merchán. The Pleurobrachia bachei was fixed in Rain X for one hour at room temperature 4. 1.5% lugol iodine solution was added to the sample for contrast staining. From the microCT scan results, shrinkage in size has been observed, but the morphology, including internal structure remains intact.