Iron reproductive toxicity of marine rotifer sibling species: Adaptation to temperate and tropical habitats.

Iron (Fe), a trace metal in coastal waters has increased significantly due to anthropogenic activities, however, few studies have examined its toxicity to marine organism reproduction and associated mechanisms. We employed two marine rotifers, the temperate Brachionus plicatilis, and tropical B. rotundiformis to investigate the toxicity of iron (FeSO•7HO) and its deleterious effects on reproductive features in females (sexual fecundity, abnormal resting eggs, and swimming speed) and males (lifespan, swimming speed, and spermatozoa quality) under lethal and sub-lethal exposure. The 24 h median lethal concentration (LC) of iron was determined as 0.9 and 1.7 μg/mL per ng of dry weight for B. plicatilis and B. rotundiformis, respectively. During sub-lethal iron (20-75 μg/mL) exposure, higher iron (≥ 20 μg/mL for B. plicatilis and ≥ 45 μg/mL for B. rotundiformis) induced rotifer sexual toxicity especially in normal resting egg development and production. These were supported by the data of male shorter lifespan, poor sperm vitality, and rotifer behavioral changes as the iron concentration increased. Iron effects on swimming behavior, slower males and faster females, should reduce male/female encounter rates associated with inactive fertilized egg (resting egg) production. Two rotifer species exhibited different iron-response patterns in genetic and enzymatic activities including iron homeostasis-maintaining related Fe-S protein, and oxidative/antioxidant related lipid peroxidation product (MDA), superoxidase dismutase/SOD, catalase/CAT, and cytochrome P450 under acute iron exposure. Antioxidant activities were vulnerable in B. plicatilis but kept activities in B. rotundiformis, which may attribute to their temperate and tropical habitat adaptations.