UV-Stressed Daphnia pulex Increase Fitness through Uptake of Vitamin D(3)

Ultraviolet radiation is known to be highly variable in aquatic ecosystems. It has been suggested that UV-exposed organisms may demonstrate enough phenotypic plasticity to maintain the relative fitness of natural populations. Our long-term objective is to determine the potential photoprotective effect of vitamin D(3) on Daphnia pulex exposed to acute or chronic UV radiation. Herein we report our initial findings in this endeavor. D. pulex survival and reproduction (fitness) was monitored for 5 d as a proof of concept study. Significantly higher fitness was observed in the D. pulex with D(3) than those without (most extreme effects observed were 0% survival in the absence of D(3) and 100% with 10 ppm D(3)). Vitamin D(3) was isolated from the culture media, the algal food (Pseudokirchneriella), and the D. pulex and quantified using high performance liquid chromatography (HPLC). Vitamin D(3) was fluorescently labeled using a phenothiazinium dye and added to cultures of D. pulex. Images demonstrating the uptake of D(3) into the tissues and carapace of the D. pulex were acquired. Our initial findings suggest a positive role for D(3) in ecosystems as both UV-stressed algae and Daphnia sequester D(3), and D. pulex demonstrate increased fitness in the presence of D(3).