Life-history strategies of Brachionus havanaensis subject to kairomones of vertebrate and invertebrate predators

Abstract

We evaluated the different life-history strategies of the rotifer Brachionus havanaensis in the presence of vertebrate (salamander axolotl, Ambystoma mexicanum) or invertebrate (copepod Acanthocyclops robustus) predator using population growth and life-table demography at two algal food levels ($0.5\ imes 10^{6}$ and 1.0×106 cells ml−1 of Chlorella vulgaris). Generally, increased food availability resulted in higher densities of B. havanaensis. At any algal food level, B. havanaensis grown in the presence of kairomones showed higher population abundances than controls. Within the kairomone treatments, rotifers grown using A. mexicanum-conditioned medium showed a higher population growth than those using A. robustus medium. The average lifespan of B. havanaensis varied from 6 to 13 d, depending on the presence or absence of kairomones and the algal food density, the shortest being in treatments containing kairomones from Ambystoma. Gross (19–22 offspring female−1) and net reproductive rates (11 offspring female−1) were significantly higher in the Ambystoma-conditioned medium than in the other treatments including controls (9–10 and 6–7 offspring female−1, respectively). Generation time (4–6 d) was influenced by algal density as well as the presence of kairomones. B. havanaensis had the shortest generation time in Ambystoma-conditioned medium. The rate of population increase of B. havanaensis varied from 0.34 to 0.87 d−1, with higher values in treatments containing Ambystoma-conditioned water. The total lorica length, anterior, and posterior spine lengths of B. havanaensis were significantly higher in the presence of kairomones from both vertebrate and invertebrate predators than in controls. In general, there was a greater lorica and spine length of B. havanaensis due to Ambystoma infochemicals than those from Acanthocyclops.