Woods H A, DeSilets R L
Biol Bull. 1997 Dec;193(3):341-349. doi: 10.2307/1542936.
Many opisthobranch gastropods embed their embryos in gelatinous egg masses; however, the functions of gel are not well known. We analyze the hypothesis that egg-mass gel protects embryos from salinity change. Using egg masses of Melanochlamys diomedea, we found that experimental removal of gel decreased the ability of embryos to survive osmotic stress. We evaluate several possible protective mechanisms by estimating osmotic influx of water into egg masses and by modeling salt efflux from an egg mass. On immersion in low-salinity water, egg masses lost roughly 23% of their mass, indicating that osmotic influx of water did not occur. Therefore, the principal route of salinity change within the egg mass is probably salt efflux. The model suggests that this efflux occurs quite slowly even when ambient salinity changes rapidly. Slow salinity change may be less stressful for embryos because the mechanisms that regulate cellular volume have more time to adjust. We show experimentally that slow salinity changes are less harmful to veligers than rapid ones by isolating capsules from egg-mass gel and exposing them to gradual or abrupt salinity change. The results support the hypothesis that rate of change of salinity is an important determinant of embryo survival and that egg-mass gel retards the rate of salinity change.
许多后鳃亚纲腹足动物将其胚胎嵌入凝胶状卵块中；然而，凝胶的功能尚不清楚。我们分析了卵块凝胶保护胚胎免受盐度变化影响这一假说。利用黑唇海兔的卵块，我们发现实验性去除凝胶会降低胚胎在渗透胁迫下的存活能力。我们通过估计水向卵块的渗透流入量以及模拟卵块中的盐分流出量来评估几种可能的保护机制。浸入低盐度水中时，卵块质量大约损失23%，这表明水的渗透流入并未发生。因此，卵块内盐度变化的主要途径可能是盐分流出。该模型表明，即使环境盐度迅速变化，这种流出也相当缓慢。缓慢的盐度变化对胚胎的压力可能较小，因为调节细胞体积的机制有更多时间进行调整。我们通过从卵块凝胶中分离出卵囊并将它们暴露于逐渐或突然的盐度变化中，实验证明缓慢的盐度变化对比目幼虫的危害小于快速变化。结果支持了以下假说：盐度变化速率是胚胎存活的重要决定因素，且卵块凝胶会减缓盐度变化速率。
