Biol Open. 2022 Oct 31:bio.059229. doi: 10.1242/bio.059229. Online ahead of print.
Plasticity in hatching time allows embryos to maximize fitness by balancing benefits and costs of remaining bound within the chorion against the benefits and costs of emerging as a free-swimming larva. In our first experiment, we exposed zebrafish (Danio rerio) embryos to either chemical cues from crushed embryos (simulating egg predation) or to blank water control. Embryos exposed to alarm cues hatched sooner with shorter body lengths and underdeveloped fins relative to larvae from the water treatment. Burst swimming speed was significantly slower for larvae that hatched from the alarm cue treatment. In a second 2 x 2 experiment, we exposed zebrafish embryos to either chemical alarm cues from conspecific embryos, mechanical disturbance (magnetic stir bar) to simulate a predator probing the substrate for developing embryos, both chemical and mechanical indicators of risk, or neither (control). We found similar effects in terms of earlier time to hatch at an earlier stage of development and poorer swimming performance of hatchling larvae. In the second experiment these effects occurred in response to mechanical disturbance with or without the presence of chemical alarm cues. Alarm cues alone produced no effects in the second experiment. Taken together, these data indicate that zebrafish embryos demonstrate a facultative tradeoff between risk of predation acting on two stages of their life history.