Inter-species sex: male-inducing experiments with the rotifer Keratella cochlearis

In the genus Brachionus (Monogononta) the switch from asexual to sexual reproduction is triggered by a chemical signal produced by the species. In Brachionus, the main environmental trigger for production of this chemical cue is crowding but for other rotifer species daylight or dietary quality may also serve as trigger. The species-specific property of the signal is variable depending on genetic relatedness of the trigger responding species. We performed male-induction experiments with different cryptic species of the monogonont rotifer Keratella cochlearis. Cryptic species were identified by the Generalized Mixed Yule Coalescent model. We performed a set of laboratory experiments in chambers of 20 mL volume separated by a 30 μm mesh where chemical releasing (trigger) species and receiving (response) species were present, respectively. Because the nature of the sex-inducing chemical is not known, this approach allowed us to expose different cryptic species of K. cochlearis by almost direct contact, mimicking natural conditions. We discuss our results in the light of genetic relatedness of the tested cryptic species and compare our results to Brachionus.