Stoichiometric dietary contraints influence the response of copepods to UVR induce oxidative stress

SOUZA, M. S.; MODENUTTI, BE; CARILLO, P.; VILLAR ARGAIZ, M.; MEDINA SANCHEZ, M.; BULLEJOS, F.; BALSEIRO, E.

LIMNOLOGY AND OCEANOGRAPHY

AMER SOC LIMNOLOGY OCEANOGRAPHY

Año: 2010 vol. 53 p. 1024 - 1032

0024-3590

We carried out field experiments in two clear mountain lakes of both hemispheres (Lake Los Cántaros, Patagonia Argentina, and Lake La Caldera, Sierra Nevada Spain) performing a full factorial design (light x nutrients: unfiltered sun light (UVR: ultraviolet radiation treatment)  and screened sunlight (>380 nm) (PAR: photosynthetically active radiation treatment), with and without nutrient enrichment). We analyzed the direct effect of UVR on enzymatic antioxidant responses (catalase [CAT], glutathion S-transferase [GST], and glutathion reductase [GR]) of two calanoid copepod species: Boeckella gibbosa and Mixodiaptomus laciniatus, and the indirect effects of food quality (carbon:nutrient ratio) potentially affecting body elemental compositions and hence enzymatic activities. Responses for the three enzymes were different: GST increased its activity under UVR exposure in the two copepods; CAT activity was null and showed no response, and GR activity differed between species. Light treatments also affected sestonic elemental ratios; UVR exposure lowered carbon:phosphorus (C:P) ratios, which in turn affected  the C:P elemental compositions of the copepods.  However, nutrient addition had different effects on the two species; it did not affect final somatic C:P ratio of B. gibbosa but had a substantial effect on body elemental composition of M. laciniatus. Finally, the relationship between grazer’s C:P ratio and GST antioxidant enzyme activity was negative. UVR and nutrient inputs affected food quality, grazer somatic stoichiometry, and subsequently enzymatic responses. The ability of calanoid copepods to overcome increased UVR may depend, at least for GST, on the elemental nutrient balance of the food.