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 response of the sand dollar Dendraster excentricus to increased temperature and reduced salinity at levels comparable to those induced by summer freshwater input into the San Juan Archipelago, Washington. We observed that embryos exposed to temperature and salinity stress exhibited polyembryony (the splitting of one embryo into multiple independent individuals), and we subsequently tested the competency of twin and normal embryos to reach metamorphosis. We found that twin embryos generated from a single egg are each capable of reaching metamorphosis. To begin investigating the mechanisms underlying polyembryony, we tested whether osmotic stress caused swelling of the fertilization envelope, thus allowing embryos the physical space to produce multiples within a single envelope. We also tested whether reduced calcium levels in low-salinity seawater reduced cell-cell adhesion and allowed cells to separate and develop as multiple embryos within a fertilization envelope. However, neither osmotic stress nor reduced calcium levels alone appear sufficient to induce polyembryony. We hypothesize that changes in the properties of the hyaline layer that lies beneath the fertilization envelope facilitate polyembryony.

中文翻译：

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Sand Dollar Dendraster excentricus 温度和盐度胁迫的发育后果

在近岸栖息地居住、繁殖和发育的动物经常暴露于非生物条件的强烈波动中，包括温度和盐度。我们研究了沙美元 Dendraster excentricus 对温度升高和盐度降低的发育反应，其水平与夏季淡水输入华盛顿圣胡安群岛引起的水平相当。我们观察到暴露在温度和盐度胁迫下的胚胎表现出多胚现象（一个胚胎分裂成多个独立的个体），我们随后测试了双胞胎和正常胚胎达到变态的能力。我们发现由单个卵子产生的双胞胎每个都能达到变态。为了开始研究多胚现象的机制，我们测试了渗透压力是否会导致受精包膜膨胀，从而使胚胎在物理空间内在单个包膜内产生倍数。我们还测试了低盐度海水中钙含量的降低是否会降低细胞间粘附并允许细胞在受精包膜内分离并发育为多个胚胎。然而，单独的渗透压力和降低的钙水平似乎都不足以诱导多胚现象。我们假设位于受精包膜下方的透明层特性的变化促进了多胚现象。我们还测试了低盐度海水中钙含量的降低是否会降低细胞间粘附并允许细胞在受精包膜内分离并发育为多个胚胎。然而，单独的渗透压力和降低的钙水平似乎都不足以诱导多胚现象。我们假设位于受精包膜下方的透明层特性的变化促进了多胚现象。我们还测试了低盐度海水中钙含量的降低是否会降低细胞间粘附并允许细胞在受精包膜内分离并发育为多个胚胎。然而，单独的渗透压力和降低的钙水平似乎都不足以诱导多胚现象。我们假设位于受精包膜下方的透明层特性的变化促进了多胚现象。