Dietary acquisition of photoprotective compounds (mycosporine-like amino acids,carotenoids) and acclimation to ultraviolet radiation in a freshwater copepod

We experimentally tested the hypothesis that accumulations of dietary compounds such as carotenoids or UV-absorbing mycosporine-like amino acids (MAAs) protect against natural levels of ultraviolet radiation (UVR).
Acalanoid copepod, Leptodiaptomus minutus, was collected from a relatively UV-transparent lake in Pennsylvaniawhere levels of copepod MAAs and carotenoids vary during the year (MAAs high/carotenoids low in summer).Animals raised in the laboratory under different diet/UVR treatments accumulated MAAs from an MAA-producingdinoflagellate but not from a cryptomonad that lacks them. The acquisition efficiency increased under exposure toUVR-supplemented photosynthetically active radiation (PAR, 400–700 nm), yielding MAA concentrations up to0.7% dry weight compared with only 0.3% under unsupplemented PAR. Proportions of individual MAAs differedbetween the animals and their diet. Shorter wavelength absorbing palythine and shinorine (max320 and 334 nm,respectively) were disproportionately accumulated over usujirene and palythene (maxca. 359 nm). Carotenoidsaccumulated under UVR exposure (to 1% dry weight) when dietary MAAs were not available. Tolerance of ultra-violet-B (UV-B) radiation was assessed as LE50s (UV exposure giving 50% mortality after 5 d) following 12-hacute exposure to artificial UV-B radiation. LE50s increased 2.5-fold for UV-acclimated, MAA-rich animals, butonly 1.5-fold for UV-acclimated, carotenoid-rich animals. Compared with carotenoids, MAAs offer this copepod amore effective photoprotection strategy, potentially as important as photorepair of DNA damage, to promote tol-erance of natural levels of UV-B radiation.
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