RESUMEN
Elevated microcystin-LR (MC-LR) and ammonia (NH3-N) concentrations co-occur during the degradation of Microcystis blooms, and are toxic to aquatic organisms. The freshwater rotifer, Brachionus calyciflorus, was exposed to mixtures of MC-LR (0, 10, 30, and 100µgL-1) and NH3-N (0, 270, and 540µgL-1) to assess the combined effects of the two toxicants on reproductive performance and phenotype traits. Single solutions of MC-LR (100µgL-1) and NH3-N (540µgL-1) had negative effects on rotifer reproductive timing and fecundity. Pre- and post-reproductive periods fluctuated with MC-LR and NH3-N concentrations, while reproductive period and total offspring per female were reduced in mixtures of MC-LR and NH3-N (p < 0.05). Grazing rate of rotifers decreased with grazing time and concentrations of the two toxicants (p < 0.001). MC-LR in combination with NH3-N had negative effects on swimming speed and body length but positively stimulated posterolateral spine development (p < 0.001). MC-LR and NH3-N had synergetic interactive effects on pre-reproductive period, reproductive period, total offspring per female, grazing rate, swimming speed, and body length (p < 0.05). In contrast, these effects were antagonistic on post-reproductive period and posterolateral spine length (p > 0.05). These results indicate that MC-LR and NH3-N act synergistically and antagonistically in causing toxicity to B. calyciflorus regarding reproductive performance and the formation of defensive phenotypes.
Asunto(s)
Amoníaco/toxicidad , Microcistinas/toxicidad , Rotíferos/efectos de los fármacos , Contaminantes Químicos del Agua/toxicidad , Animales , Tamaño Corporal/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Sinergismo Farmacológico , Femenino , Agua Dulce/química , Toxinas Marinas , Fenotipo , Reproducción/efectos de los fármacos , Rotíferos/crecimiento & desarrollo , NataciónRESUMEN
Toxicants released during the degradation of cyanobacterial blooms, such as microcystin-LR (MC-LR) and nitrite (NO2-N), affect the growth of aquatic organisms. The freshwater rotifer Brachionus calyciflorus was exposed to solutions with different combined concentrations of MC-LR (0, 10, 50, 100, and 200µgL-1) and NO2-N (0, 2, 4, 6, and 8mgL-1) to assess the combined effects of MC-LR and NO2-N on life cycle parameters and oxidative stress. Single solutions of MC-LR 200µgL-1 and NO2-N 8mgL-1 were toxic to rotifers. MC-LR combined with NO2-N decreased population growth rate (r), survival, and reproduction, but increased reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH) contents (p<0.01). Superoxide dismutase (SOD) and catalase (CAT) activities and mRNA expression levels of MnSOD, CuZnSOD, and CAT significantly decreased under high concentrations of MC-LR or NO2-N (p<0.05). ROS levels had negative correlations with antioxidant enzyme activities and expression levels of antioxidant genes (p<0.01). MC-LR and NO2-N had interactive effects on r, reproduction, ROS levels, MDA content, SOD activity, and expression levels of MnSOD and CAT (p<0.05). By contrast, these effects were antagonistic on survival, CAT activity, GSH content, and expression level of CuZnSOD (p>0.05). Results showed that cyanobacterial metabolites act synergistically and antagonistically to cause toxicity to B. calyciflorus. ROS-mediated toxicity was considered the mechanism by which MC-LR and NO2-N induce damage.