Maternal vibration induces synchronous hatching in a subsocial burrower bug

In some egg-laying species, parents provide care by regulating the hatching pattern for embryos because the survival and growth of offspring are influenced by the timing of hatching. Burrower bugs, Adomerus rotundus (Heteroptera: Cydnidae) exhibit maternal care including defence against predation and provision of food. We found that A. rotundus mothers displayed physical vibration (shaking the body rhythmically) while maintaining the egg-guarding posture, i.e. holding the egg mass under the thorax between the forelegs and midlegs. We sought to ascertain whether A. rotundus mothers induce synchronous hatching by this physical vibration. The peak in maternal vibrations coincided with the time when most embryos hatched from their eggs. To investigate the effect of the presence of a mother on hatching synchrony, we conducted an experiment in which the mother was removed immediately before hatching. The control broods, which experienced continuous guarding from the mother, hatched synchronously, while the experimental broods, which had been isolated from the mother, hatched more asynchronously. To ascertain whether embryos hatch specifically in response to the vibrational signal, we exposed mature egg masses to an artificial vibration and monitored hatching patterns. The artificial vibration induced synchronous hatching. These results strongly suggest that A. rotundus mothers promote synchronous hatching actively using physical vibration.