Environmental Induction of Polyembryony in Echinoid Echinoderms

Polyembryony, or the production of multiple offspring from a single zygote, is a widespread phenomenon in the animal kingdom. Various types of polyembryony have been described in arthropods, bryozoans, chordates, cnidarians, echinoderms, and platyhelminthes. We describe the induction of polyembryony in embryos of the sand dollar Echinarachnius parma and the pencil urchin Eucidaris tribuloides in response to elevated temperature and reduced salinity. Data on the environmental variation in temperature and salinity that normally occurs during the spawning season, combined with the range of laboratory conditions over which polyembryony was induced, suggest that polyembryony may occur frequently in these species under natural conditions. We tested an additional two species of echinoids for similar responses, but found little evidence for polyembryony in the green urchin Strongylocentrotus droebachiensis or the variegated urchin Lytechinus variegatus, suggesting that polyembryony is not a universal response of echinoids to fluctuations in temperature and salinity. The unexpected developmental changes that we observed in response to present-day fluctuations in temperature and salinity suggest that ongoing and future environmental shifts may drive substantial changes in marine invertebrate developmental patterns, and that these changes will be different across taxa.