Interspecific effects of allelochemicals of 4-species of Brachionidae (Rotifera: Monogononta) on the population growth

We compared the interspecific effects of conditioned-medium containing allelochemicals from 4-rotifer species [(Brachionus calyciflorus (Pallas, 1776), Plationus patulus (Müller, 1786), Brachionus angularis (Gosse, 1851) and Brachionus havanaensis (Rousselet, 1911)] using population dynamics as a tool. All the four rotifer species were separately cultured with Chlorella at one density (1X106 cells ml-1). Each rotifer species was grown separately on the conditioned-medium for 21 days. The test medium was daily changed with fresh algal food. We found that the growth curves of the four rotifer species varied depending on the test species and the source of conditioned-medium. Depending on the test species and the origin of allelochemicals, the rate of population increase (r) varied from 0.10 to 0.65 per day. In controls, B. calyciflorus had the highest r while P. patulus had the lowest. Allelochemicals significantly decreased the population growth rates of four species in the conditioned medium, except two (no significant effect: B. havanaensis controls vs medium from B. calyciflorus and positively significant effect: B. angularis controls vs medium from B. calyciflorus). The suppression (%) in growth rate of a species from the conditioned medium of a congener was not the same, when the reciprocal test was carried out. It appeared that the allelopathic effects of brachionid-conditioned medium were species-specific.