Studies on the formation and hatching of fertilized eggs of the rotifer Brachionus plicatilis - II. Effects of temperature and chlorinity on resting egg formation in the rotifer Brachionus plicatilis.

The effect of temperature (15-30°C) and chlorinity (4-16‰) on resting egg production of the rotifer Brachionus plicatilis was investigated. The rate of resting egg formation was found to increase at lower temperatures and chlorinities. The number of resting eggs produced by 10, 000 rotifers at 15°C and 4‰ Cl' was 8, 300, as opposed to 6.1 at 30°C and 16‰ Cl'. Further, the steps which precede egg formation, i.e., appearance of mictic females, fecundity of male-producing mictic females, mating and fecundity of resting egg-producing females, were activated at lower temperatures and chlorinities. The fecundity of each female type and the lifetime swimming distance (life span×swimming speed) of males increased at lower temperatures and chlorinities. These factors were used as an index of biological activity. The data demonstrate a concurrence of optimum conditions for resting egg production with rotifer biological viability. This suggests that greater numbers of mictic females occur and more resting eggs are formed when the individual rotifers are physiologically vigorous.