Effects of cladoceran-conditioned medium on the demography of brachionid rotifers (Rotifera: Brachionidae)

Abstract

Rotifers and cladocerans compete for resources in freshwater ecosystems. Cladocerans, due to their large size, are competitively superior to rotifers. Cladocerans also release secondary metabolites into the medium which may be allelopathic to rotifers. However, in many eutrophic water bodies, rotifers are competitively dominant to cladocerans. We therefore hypothesize that allelochemicals released by competing species of Cladocera have weak or no adverse effects on rotifers. To test this, we conducted cohort life table demography experiments of the three rotifers Brachionus calyciflorus, Brachionus havanaensis, and Plationus patulus with cladoceran-conditioned medium (CM) derived from Moina macrocopa, Ceriodaphnia dubia, and Daphnia pulex. All six zooplankton species were isolated at the same time from a shallow eutrophic water body in Central Mexico. We found that the following demographic variables of B. calyciflorus cultured in CM did not differ from controls: life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase. We further showed that B. havanaensis was most sensitive to the cladoceran-mediated chemicals and that M. macrocopa-CM caused varied demographic responses in rotifers. We conclude that cladoceran-conditioned medium had weak allelopathic effects on rotifers unlike the negative experience from direct physical contact with Cladocera.