Interactive effects of microcystin and ammonia on the reproductive performance and phenotypic traits of the rotifer Brachionus calyciflorus

- MC-LR combined with NH3-N was detrimental to Brachionus calyciflorus reproduction.
- Rotifer feeding and swimming behaviors were inhibited under MC-LR and NH3-N stress.
- Rotifer defensive phenotypes were induced in response to MC-LR and NH3-N.
- MC-LR and NH3-N act synergistically and antagonistically to cause toxicity.

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 100 µg L−1) and NH3-N (0, 270, and 540 µg L−1) to assess the combined effects of the two toxicants on reproductive performance and phenotype traits. Single solutions of MC-LR (100 µg L−1) and NH3-N (540 µg L−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.