Photoprotective compounds in weakly and strongly pigmented copepods and co‐occurring cladocerans

Abstract

1. The prevalence of mycosporine-like amino acids (MAAs) -a group of potential ultraviolet (UV)-photoprotective compounds -was surveyed across 11 species of freshwater copepods from 20 lakes of varying ultraviolet radiation (UVR) transparency in North America, New Zealand and Argentina. Co-occurring cladocerans were also analysed (seven species from 12 lakes). Many of the calanoid copepod populations were red with carotenoid pigmentation, allowing comparison of MAA and carotenoid accumulation as photoprotective strategies. 2. In two Pennsylvania (U.S.A.) lakes, MAA and carotenoid contents were followed during the early spring to mid-summer period of lake warming. A pronounced seasonal pattern of higher carotenoid/low MAA content in spring, shifting to low carotenoid/higher MAA content in summer, was observed in calanoids from the more UV transparent lake. 3. All copepod samples contained MAAs. Visibly red calanoids, especially southern Hemisphere Boeckella, often had moderate to high concentrations (2.5-11 lg MAA mg )1 dw), but low concentrations (0.04-1 lg MAA mg )1 dw) in some N. American red calanoids show that high carotenoid pigmentation (e.g. 5-10 lg carotenoid mg )1 dw) does not necessarily imply high MAA content. 4. No cladoceran sample had more than trace amounts of MAAs (<0.05 lg mg )1 dw). Therefore, MAA accumulation does not seem to be a photoprotective strategy utilized by Daphnia (five species from nine lakes) or other cladocerans. 5. Seven identifiable MAAs were widely distributed among both calanoids and cyclopoids. Shinorine was ubiquitous and was usually the most abundant MAA in N. American samples. In contrast, porphyra-334 was the predominant MAA in the southern Hemisphere Boeckella. 6. Copepods from higher UVR lakes tended to have a higher MAA content, but this relationship was statistically weak overall and taxon-specific when found.

UV photoprotectants in arctic zooplankton

“…Copepods had astaxanthin as the main pigment in their body, and their concentration of total carotenoids was significantly higher than that of cladocerans (average ± SE: 2.6 ± 1.4 µg mg -1 and 1.0 ± 0.5 µg mg -1 ; F = 8.8, p = 0.007). This is in accordance with the recent study of Persaud et al (2007), in which copepods had a total carotenoid concentration of 3.0 µg mg -1 , and cladocerans, 0.02 µg mg -1 . Several other studies have also reported higher carotenoid concentrations in copepods relative to cladocerans (Hairston 1979b, Partali et al 1985, Hessen & Sørensen 1990, Hansson 2004) and have related this to variation in the susceptibility to different wavelengths, food compositions and availabilities.…”

“…More recent studies have also concluded that pigmented individuals survive better than pale individuals when exposed to UV radiation (Hairston 1976, Hessen 1996, and that there is a strong seasonal variation in pigment content. Subarctic Daphnia umbra synthesize melanin only during summer months, beginning immediately after ice-out (Rautio & Korhola 2002), and alpine copepods peak in their mycosporine-like amino acid (MAAs) concentrations during the open-water period (Tartarotti & Sommaruga 2006, Persaud et al 2007). Pigments and the colourless MAAs in zooplankton are mostly considered to be UV photoprotectants (Perin & Lean 2004), acting together with other photoprotectants such as antioxidants and with behavioural responses such as vertical migration.…”

UV‐enhanced fish predation and the differential migration of zooplankton to UV radiation and fish

“…Nevertheless, surface avoidance in both Daphnia and L. minutus may ultimately still be related to UVR because of vulnerability to either UV damage or UV-foraging predators. Lake Giles D. catawba are substantially less pigmented than L. minutus (Persaud et al 2007). Although decreasing their visibility to visual predators, this lack of pigmentation increases susceptibility to damaging solar radiation, which can evoke downward daytime migrations (Leech and Williamson 2001;Boeing et al 2004;Cooke et al 2008).…”

“…To our knowledge, M. salmoides has not been examined for UV photoreceptors; however, UV photoreceptors have been detected in other teleost species such as Lepomis, Perca, Salmo, and Oncorhynchus (Loew et al 1993;Browman et al 1994;Leech and Johnsen 2003). Though not directly tested, UVR may be contributing to the enhancement of prey detection in our experimental columns, particularly on species with photoprotective compounds such as copepods (Moeller et al 2005;Persaud et al 2007).…”

“…Moreover, copepods often contain higher concentrations of photoprotective compounds compared to cladocerans (Tartarotti et al 2001;Hansson et al 2007;Persaud et al 2007). In Lake Giles, copepod MAA concentrations increase from spring through summer, whereas carotenoid concentrations decrease (Moeller et al 2005;Persaud et al 2007). Copepods with high MAA concentrations may appear particularly dark against a UV-rich background and thus more susceptible to predators with UV vision (Loew and McFarland 1990;Leech and Johnsen 2003).…”