Embryo Chemical Alarm Cues Delay Time to Hatch by Annual Killifish (Nothobranchius spp.)

Annual killifishes of the genus Nothobranchius live in seasonal water bodies in Eastern Africa. Adults die at the end of the rainy season when seasonal pools desiccate but diapaused embryos persist in the sediments and hatch in subsequent rainy seasons. Embryos use environmental cues to determine optimal hatching conditions to begin a new generation. We simulated a predation event by crushing Nothobranchius embryos and tested if embryos of N. eggersi and N. foerschi adjust time of hatching in response to these chemical cues. We placed individual diapause III embryos in cups of dechlorinated water dosed with either (1) blank water, (2) odor of crushed chironomids, or (3) odor of crushed Nothobranchius embryos. Although N. eggersi Red embryos hatched at a significantly faster rate than embryos from N. eggersi Solid blue or N. foerschi, the effect of the cue was consistent for all three types of Nothobranchius embryos used in this study. The odor of crushed Nothobranchius embryos caused a significant delay in time to hatch relative to the two control treatments. These data suggest that Nothobranchius embryos attend to chemical alarm cues derived from crushed conspecific embryos and delay hatching as a bet-hedging strategy to avoid hatching when they detect risk of predation.