Rotifer adaptation to the unpredictability of the growing season

Sexual reproduction in cyclically parthenogenetic rotifers results in the production of diapausing eggs that tolerate harsh conditions. Theory predicts that the adaptation to environmental unpredictability can occur by the evolution of bet-hedging strategies. When facing unpredictability in the length of rotifer growing season, patterns of diapausing egg production and hatching can disperse risks and act as bet-hedging strategies. Here, we identified the methodologies to test bet-hedging theory and summarized predictions on rotifer diapause traits. We assessed these predictions by reviewing and reanalyzing results from other studies on field and experimentally evolving populations of Brachionus plicatilis from Spanish ponds. These studies include (1) a quantification of the unpredictability in field populations, (2) the measurement of diapause-related traits in laboratory conditions, and (3) genomic data. The view arising is that these rotifers adaptively respond to the unpredictability in their localities. As expected, propensity for sex increased with unpredictability. Hatching fractions of diapausing eggs were intermediate and decreased with unpredictability only in experimentally evolving populations. In field populations, genetic variance in the focal traits did not increase with unpredictability. Finally, environmental features and diapause-related traits are associated to suites of specific genes, although the molecular mechanisms linking these genes with life history are still unknown.