Timing of sexual reproduction in rotifer life cycles: generation-based models for environmental and endogenous control

ABSTRACT Sexual reproduction and consequent diapause in the heterogonic life cycle of monogonont rotifers is controlled by both environmental and endogenous factors. Environmental signals known to induce the transition from exclusive female parthenogenesis to some bisexual reproduction are high population density, dietary tocopherol or photoperiod. In clonal populations initiated by stem females hatched from fertilized resting eggs, environmental control can be endogenously suppressed in early generations, and endogenous induction of sex can occur automatically in all or just later generations. Here, simple empirical models for different rotifers illustrate how commitment to sex over multiple generations can be determined by the interplay of these environmental and endogenous factors. The models are discussed regarding experimental support, and the ecological significance of control mechanisms. In natural populations, there are many challenges involved in determining and interpreting patterns for the timing of sexual reproduction during growing seasons. The propensity for sex can be difficult to quantify, and mechanisms responsible for the timing and commitment to sex may be difficult to identify without complementary laboratory experiments. Future studies with additional species from a variety of habitats are needed.