Oxidative stress in the copepod Boeckella gracilipes in Andean Lakes: intraespecific differences

BALSEIRO, E.; M.S. SOUZA; C. LASPOUMADERES; B. MODENUTTI; M. BASTIDAS NAVARRO; F. CUASSOLO

Global Change and the World’s Mountains - Extended Abstracts

Global Change and the World’s Mountains

Año: 2010; p. 681 - 682

In freshwater systems, ultraviolet radiation (UVR) is recognized as an important biological stressor. UVR can penetrate within the euphotic zone affecting aquatic organisms’ physiology in different degrees, and in particular it is recognized that shorter wavelengths (UV-B, 280-315 nm) are more deleterious than longer ones (UV-A, 320-400nm). Planktonic organisms have developed a variety of photoprotection strategies including behavioral avoidance of photodamage, production or incorporation of UV-absorbing compounds as carotenoids, melanin, and Mycosporine-like Amino Acids (MAAs), and enzymes involved in DNA repair and in antioxidant defenses. Among the latter, glutathione S-transferases (GST), is a detoxifying enzyme involved in the removal of reactive organic hydroperoxides, such as the products of lipid peroxidation under oxidative stress. Antioxidant mechanisms are energetically demanding and may require additional elemental supplies, as phosphorus (P) for antioxidant enzymes. Thus, the relative importance and efficiency of UVR defenses would depend on the availability of dietary factors, such as P and N. Among the deleterious effect on proteins, UVR oxidant injuries might affect specific enzymatic endpoints such as acetylcholinesterase (AChE). AChE catalyzes the hydrolysis of acetylcholine (ACh), the primary neurotransmitter in sensory and neuromuscular systems in most species. The interaction between ACh and AChE is vital for normal behavior and muscular function. Although natural factors such as UVR may also influence this enzyme activity, there are few data of direct effects of UVR on the enzyme activity on natural populations of planktonic organisms. Boeckella gracilipes is the dominant copepod species in many Andean North Patagonian lakes. In these lake ecosystems, the high C:P ratios are associated with high light-phosphorus ratios, thus, organisms living in these transparent lakes would be constrained by potentially hazardous ultraviolet radiation (UVR). We analyzed natural populations that showed intraespecific differences in photoprotective pigments (carotenoids and mycosporine-like amino acids), elemental ratios (C:N:P) and in antioxidant enzyme activities. Performing field and laboratory exposure experiments we determined the response to UVR in population inhabiting different lakes (medium and high altitude lakes). In particular, we analyzed the response of antioxidant enzymes (GST) and the detrimental effects of UVR on Acetylcholinesterase (AChE). We were able to determine that natural populations of the same species exhibited differences in the response to UVR. Although carotenoid concentration was higher in organisms inhabiting fishless high altitude lakes, GST activity was also higher in these copepods than in low altitude and less transparent ones. However, in the former there was no UVR effect on acetylcholinesterase whereas a reduction in the activity was observed in the colourless copepods, confirming that AChE activity would depend more on the antioxidant capacity (GST) for enzyme synthesis than on the photoprotective compounds. Nevertheless, during laboratory incubations the pigmented copepods exhibited up to 30% of individuals with damage on antenna 1, suggesting that these copepods were also indeed affected by UVR. Because calanoid copepods depend on swimming for escape reaction and feeding currents, a dysfunction of AChE would affect copepod’s fitness, as it would affect their motility patterns. Motion is not a singular event; it result from the integrated function of several reaction components that imply multiple nerve impulses accurately coordinated. Thus, any alteration in neurotransmitter mechanisms, as acetylcholinesterase, will have strong negative effect on this vital function. Our results indicated that the level of GST activity resulted a key in the protection of AChE, and that GST activity level depends on the food stoichiometry (C:P ratio), thus high C:nutrient ratios will increase risk of UVR damage on the neurotransmitter system.