Effect of conditioned media on the asexual reproduction of the monogonont rotifer Brachionus plicatilis O. F.!Muller

We carried out several individual cultures of the rotifer Brachionus plicatilis to determine the effects of conditioned medium on its asexual reproductive characteristics, such as age and body size at first amictic egg production, age at first reproduction, duration of embryonic development, lifespan, intrinsic rate of natural increase, fecundity schedule and lifetime fecundity. Rotifers were precultured at a series of densities ranging from 0 to 50 ind. ml(-1) for 0-60 h and 0.45 mu m filtrates of these culture media were used as conditioned media. In the conditioned media with higher rotifer densities during preculture, the age at first egg production and first reproduction and duration of embryonic development became shorter than those of the control (fresh medium). Both the age at first egg production and first reproduction negatively correlated with the rotifer densities of the preculture. Animals in conditioned media completed their maturation at smaller body sizes and showed higher intrinsic rates of natural increase (r). They exhibited an earlier fecundity schedule (m(x)), but with a lifespan shorter than that of the control animals. Lifetime fecundity (R-0) did not differ between animals in the conditioned media and in the control. These results suggest that conditioned media accelerate the life history parameters related to reproduction.