Meeting Abstract
Animals that reside, reproduce, and develop in nearshore habitats are often exposed to strong fluctuations in abiotic conditions, including temperature and salinity. We studied the developmental responses of five echinoid echinoderms (sea urchins and sand dollars) to increased temperature and reduced salinity. We aimed to document two recently described phenomena: delay of hatching (DOH) and polyembryony. First, we found that DOH is a widespread response to reduced salinity. Hatching was delayed by 79% in Echinarachnius parma, 26% in Strongylocentrotus droebachiensis, 22% in Lytechinus variegatus, and 17% in Dendraster excentricus. Only embryos of Arbacia punctulata failed to delay hatching in response to reduced salinity. Second, we observed polyembryony in both of the irregular echinoids studied (E. parma and D. excentricus). In D. excentricus, we tested the competency of twinned and normal embryos to reach metamorphosis. We found that twin embryos generated from a single egg are both capable of reaching metamorphosis. To investigate the mechanisms underlying polyembryony, we tested whether reduced Calcium levels in low salinity seawater reduce cell-cell adhesion and allow cells to separate and develop as multiple embryos within a fertilization envelope. We also tested whether osmotic stress caused swelling of the fertilization envelope, allowing embryos more room to produce multiples, or delay hatching into a later, larger stage. However, neither reduced Calcium levels nor osmotic stress alone appears sufficient to induce polyembryony. We currently hypothesize that the swelling of the hyaline layer within the fertilization envelope may facilitate polyembryony.
