DOI: 10.20350/digitalcsic/3739
title: When Parasites are Good for Health: Cestode Parasitism Increases Resistance to Arsenic in Brine Shrimps

description: LC50 tests: Naturally infected and uninfected adults of A. parthenogenetica were collected with a plankton net (0.5 mm) within the Odiel saltpan complex. Sampling was carried out on two dates (14th of April and 15th of May 2014). Toxicity experiments were conducted after 24 h of acclimation of the Artemia at 100 g/l salinity. Two experiments were carried out. The first (with Artemia collected on 14th of April) was conducted at 25ºC. The second (Artemia collected on 15th of May) was conducted at both 25 and 29ºC. Median lethal concentration (LC50) was used to quantify Aresenic toxicity in infected and uninfected adult Artemia. Ten concentrations of As between 5 and 140 mg/l were used for the experiments at 25ºC (0, 5, 20, 35, 50, 65, 85, 95, 110, 125, 140 mg/l), and ten between 4 and 67 mg/l were used for the experiment at 29°C (0, 4, 11, 18, 25, 32, 39, 46, 53, 60, 67 mg/l) in order to estimate the LC50. Three replicates were used per concentration, with each replicate made up of a group of 10 individuals. Prevalence (P) and mean abundance (MA) were calculated separately for the “infected group” on both dates. Oxidative stress analysis and lipid droplet quantification: Artemia were sampled in May 2015 from Odiel salt ponds. A subsample was used to characterize the exact parasite composition (n = 60 infected individuals) and quantify the number of lipid droplets (n = 20 infected and 20 uninfected Artemia). The numbers of cysticercoids, prevalence, mean abundance and mean intensity were calculated for each cestode species. The number of lipid droplets was estimated according to Wurtsbaugh & Gliwicz 2001 [86]. We quantified lipid levels by inspecting individuals at 30x magnification and counting the number of lipid droplets along the right side of the 5th and 6th segments of the body. The rest of the specimens were acclimated during 24h to the experimental salinity with continuous aeration and fed ad libitum with lyophilized Tetraselmis chuii algae. The toxic concentrations of 4.69 mg/l As was selected on the basis of preliminary LC50 tests. Infected and uninfected A. parthenogenetica of the same size range were allocated to 1L glass vials (100 individuals per vial) with 600 ml of experimental solution (either control (no toxic solution) or 4.69 mg/L As) during 24h at 25 ºC (12:12 photoperiod) without food. After 24h exposure, individuals were stored at ‒80℃ until biochemical analysis. We performed the biochemical analysis on pools of 20 individuals per treatment. Number of replicates varied from 1 to 12 depending on Artemia availability. The different biomarkers were determined in the whole soft tissues after homogenization and centrifugation. We quantified five parameters as a proxy for oxidative status of Artemia: activity of four enzymes (catalase CAT, superoxide dismutase SOD, glutathione peroxidase GPx and glutathione reductase GR) and lipid peroxidation levels (thiobarbituric acid reactive substances TBARS). Total protein content in the supernatant fluid was determined following a standard Bradford’s procedure. Enzyme activity was determined colorimetrically. Address questions to Marta I Sánchez, e-mail: marta.sanchez@ebd.csic.es