Effect of juvenile hormone and serotonin (5-HT) on mixis induction of the rotifer Brachionus plicatilis Muller

Juvenile hormone (JH) and serotonin (5-HT) were previously shown to enhance mictic (sexual) female production of the rotifer Brachionus plicatilis in batch cultures. To explore the basis of these effects, experiments were con ducted on isolated individuals. JH treatment of maternal rotifers with 5 an d 50 mu g ml(-1) (18.8 and 187.7 mu M) resulted in significantly higher (P < 0.05) mictic female production in the second (F-2) and third (F-3) genera tions. JH treatment was effective even at a lower food concentration of 7 x 10(5) cells ml(-1), but it was not effective when free ammonia was added a t 2.4 and 3.1 mu g ml(-1). Mictic female production was not increased with exposure to 5-HT up to 50 mu g ml(-1) (129.1 mu M) concentrations. When foo d level was reduced to 7x 10(5) cells ml(-1), however, 5-HT-treated rotifer s produced significantly (P < 0.05) more mictic females than the control, p articularly in F-3 generation. Mictic female production of 5-HT-treated rot ifers did not differ from that of the control with or without free ammonia, but the intrinsic rate of natural increase (r) of 5-HT-treated rotifers at 3.1 mu g ml(-1) free ammonia was significantly higher than the control. Th ese results show that juvenile hormone increases mictic female production u nder optimum and sub-optimum food levels, whereas 5-HT increases both micti c female production at low food level and population growth rate at high fr ee ammonia concentrations. These compounds could he used to manage rotifer cultures and probe the mechanisms controlling the rotifer life cycle as it switches to mictic reproduction. (C) 2000 Elsevier Science B.V. All rights reserved.