Maternal Inhibition of Hatching at High Population Densities inTigriopus japonicus(Copepoda, Crustacea)

A new mode of maternal protection is described for organisms that maintain contact with their developing embryos until hatching. Females of the copepod Tigriopus japonicus inhibit hatching of mature embryos (nauplii) from eggs they carry. Inhibition occurs at high population densities, or in the medium from crowded cultures. In contrast, when the mothers are killed or detached from their mature egg-sacs, all nauplii hatch within an hour, even in media from high-density cultures. A structure probably serving as an "umbilical cord" for transmission of the inhibitory message was demonstrated using electron microscopy.