Hypoxia extends lifespan of Brachionus manjavacas (Rotifera)

Work by Maria Rosa Miracle's group in 1989 described the adaptation of natural Brachionus plicatilis populations to low oxygen in oxyclines of meromictic lakes. This adaptation was accomplished by slowing metabolism in hypoxia, altering reproductive schedules and extending generation times. Many years later, Miracle's work inspired us to examine whether hypoxia could extend rotifer longevity and reproduction in our study of the biology of aging. In this paper we show that exposure of rotifers to four days of an atmosphere of 1.6 % O-2 extended mean lifespan 107 % over controls in normoxia (20.9 % O-2), whose mean lifespan was 7.9 days. Alternating days of hypoxia and normoxia also markedly extended rotifer lifespan by 53 %. Exposure to 1.6 % O2 hypoxia nearly doubled lifetime reproduction of females (24.3 vs 12.4 offspring in control). Hypoxia exposure protected rotifers from subsequent oxidative and UV stress, but not starvation, osmotic or heat stress. The 0-4 day age-classes responded best to hypoxia exposure as compared to hypoxia exposure days 4-8 or 8-12. The protective effects of two days of hypoxia exposure persisted through day 6, then vanished by day 8. Rotifer diapausing eggs are especially resistant to hypoxia and hatch in atmospheres containing as little as 1.6 % O-2 after a one day delay. Our conclusion is that exposure to hypoxia for four days in the youngest age classes extends rotifer longevity and enhances lifetime reproduction. This response has adaptive value in anoxic sediments where most rotifer diapausing eggs are deposited.