Abstract

Startle responses are widespread in animals and require neural circuitry to control fast whole-body responses. To dissect the genetic and circuit bases of such coordinated whole-body responses we study a startle response to water-born vibrations in a marine larva. We found that upon water vibrations larvae of the annelid Platynereis arrest locomotor cilia, and simultaneously contract the body and elevate all segmental parapodia. The startle response is mediated by collar receptor neurons expressing the polycystin channels PKD1 and PKD2 . CRISPR-generated PKD1 and PKD2 mutant larvae do not startle and fall prey to a copepod predator at a higher rate. Reconstruction of the whole-body connectome of collar receptor circuitry revealed parallel feed-forward circuits to ciliary bands and muscles. The wiring diagram suggests circuit mechanisms for the intersegmental and left-right coordination of the startle response. Our results reveal how polycystin-mediated mechanosensation can trigger a coordinated whole-body effector response involved in predator avoidance.