Divergent responses in morphology and life history to an Asplanchna kairomone between attached and free-swimming Brachionus dorcas (Rotifera)

In the presence of the predatory rotifer Asplanchna, some Brachionus and Keratella species develop inducible morphological, behavioral, and life history defenses that enable prey to survive predation pressure. However, whether clones belonging to the same rotifer species but with different behaviors (attached and free-swimming) exhibit divergent responses in morphology and life history remains largely unknown. In this study, neonates of an attached and a free-swimming clone of B. dorcas were exposed to media conditioned by A. brightwellii neonates at densities of 0 (control), 40, 80, and 160 ind l−1 for 24 h, and their morphological and life-table demographic parameters were measured and calculated. We showed that the Asplanchna kairomone significantly increased the propensity to attach in the attached clone only, with attached individuals effectively protected from Asplanchna predation. In response to increasing Asplanchna kairomone concentration, the attached clone did not show any morphological changes, but it did exhibit a decreased net reproductive rate and intrinsic rate of population increase. The free-swimming clone developed elongated posterolateral spines and a decreased intrinsic rate of population increase, as well as a decrease in the proportion of sexual offspring. Thus, both clones exhibited reproductive costs.