Low-temperature induction of sexual reproduction in rotifer Brachionus plicatilis: cyclical versus obligatory parthenogenetic strains

Specific temperature manipulation following the growth features of rotifer species was demonstrated to induce the transition of reproductive patterns. This study utilized diverse strains of Brachionus plicatilis Müller, 1786 rotifer with two distinct reproductive patterns at 25 °C (control): cyclical parthenogenesis (NH1L strain) and obligatory parthenogenesis (Amami and Obama strains). With these strains, we assessed the efficacy of low-temperature (15 °C) induction on rotifer sexual reproduction and associated molecular evidence. The three tested strains exhibited superior adaptability to low temperatures, maintained population growth at 15 °C, and rapidly expanded after being transferred to 25 °C. Moreover, exposure to 15 °C effectively induced mictic female occurrence in the Amami strain (mixis rate peaked at 41.4% on day 12) and enhanced mixis induction and resting egg production (sevenfold) in the NH1L strain. There was no sexual induction of the Obama strain under either temperature condition. Based on the molecular evidence, we hypothesized that temperature manipulation induces adaptive responses, such as activated oxidative defenses and energy metabolism, which then triggers steroid hormone signaling to initiate the sexual induction in the cyclical parthenogenesis strain. However, an obligate parthenogenic strain probably possesses greater tolerance or resilience, such as a high base level of hsp70, against environmental fluctuations, rendering it insensitive to sexual stimuli.