Physiological response and molecular mechanisms against UV-B radiation in Brachionus asplanchnoidis (Rotifera)

Ultraviolet B (UV-B, 280-320 nm) radiation is a major environmental stressor for aquatic organisms on Earth's surface. Its effects on biological systems are well known, but the mechanisms by which organisms respond and adapt to UV-B radiation are still being explored. In this study, we investigated the effects of UV-B radiation on the monogonont rotifer Brachionus asplanchnoidis, focusing on physiological parameters, antioxidant systems, DNA damage, and DNA repair-related molecular mechanism. Our results showed that the LD₅₀ was at 28.53 kJ/m², indicating strong tolerance to UV-B. However, UV-B radiation caused adverse effects on growth and reproduction, with shortened reproductive period and longevity, decreased fecundity and hatchability, and inhibition of population growth. Biochemical analyses revealed severe oxidative damage and lipid peroxidation, with increased ROS and MDA levels. Activities of antioxidant enzymes were highly induced at low doses but decreased at high doses. DNA damage also occurred in UV-B-exposed rotifers. Furthermore, selected DNA repair-related genes were up-regulated in a dose-dependent manner. These findings provide a comprehensive understanding of the effects of UV-B radiation on rotifers and highlight the importance of considering both ecological and molecular responses in assessing the impact of UV-B radiation on aquatic organisms.