Allelopathic effects of male and female calanoids and cyclopoids (Copepoda) on the demographic response of Brachionus havanaensis (Rotifera)

We hypothesized that cyclopoids, being predators, have a stronger allelopathic influence than calanoids on life-history variables of herbivorous rotifers. To test this hypothesis, we quantified the allelopathic effects of conditioned medium obtained separately from males and females of a calanoid (Arctodiaptomus dorsalis) and a cyclopoid (Mesocyclops longisetus) on the life table demography of the rotifer Brachionus havanaensis. The conditioned medium of the male and female A. dorsalis and male M. longisetus caused a significant reduction (14–18%) in the life expectancy at birth of B. havanaensis. Gross and net reproductive rates of rotifers reduced significantly on the conditioned medium of male or female A. dorsalis; however, the conditioned medium from either sex of M. longisetus had no significant effect on these variables. The population growth rate, r, varied from 0.53 to 0.64 d−1 depending on the treatment; the r was significantly lower when cultured on the conditioned medium from A. dorsalis (males or females) and female M. longisetus Contrary to our hypothesis, calanoid allelochemicals adversely affected the life history variables of rotifers more than those produced by the cyclopoids.