Segura Cristian J, Montory Jaime A, Cubillos Victor M, Diederich Casey M, Pechenik Jan A, Chaparro Oscar R
Instituto de Ciencias Marinas y Limnológicas, Universidad Austral de Chile, Valdivia, Chile.
J Comp Physiol B. 2015 Aug;185(6):659-68. doi: 10.1007/s00360-015-0908-6. Epub 2015 May 13.
Organisms that encounter stressful situations in nature often cope using behavioral (e.g., avoidance) or physiological tactics. In sessile mollusks, the only available behavioral option in dealing with salinity stress is to "clam up", isolating their tissues from the environment. Though effective in the short term, prolonged isolation can have detrimental physiological consequences, particularly for females brooding embryos in a mantle cavity that is isolated from the external environment. In the Quempillén estuary, the Chilean oyster, Ostrea chilensis, spent nearly one-third of its brooding season at salinities low enough to cause female isolation. When females thus isolated themselves, the dissolved oxygen in their mantle cavity fluid dropped to hypoxic levels within 10 min. In females that were brooding embryos, this depletion of oxygen was not uniform: oxygen was depleted more quickly in the palp region (where embryos accumulate) than in the inhalant region. Additionally, oxygen was reduced even more quickly in the palp region when females were brooding late-stage embryos, which consumed oxygen significantly more quickly than embryos in earlier developmental stages. Finally, O. chilensis used anaerobic metabolism to cope with the hypoxia induced by isolation, as lactate accumulated in the tissues of both females (brooding > non-brooding) and embryos (late stage > early stage). Our findings demonstrate the trade-off between an adaptive avoidance behavior (clamming up) and the potentially detrimental consequences brought on by such a behavior (hypoxia). Cycling of embryos throughout the mantle cavity by deliberate female pumping keeps them from accumulating in the area between the palps, forestalling the creation of hypoxic conditions there. In addition, the capacity for anaerobic metabolism by both females and their embryos should help them tolerate the low oxygen levels that do eventually arise when the pallial cavity is isolated from the surrounding environment during long periods of reduced ambient salinity.
在自然界中遇到压力情况的生物通常会采用行为（如回避）或生理策略来应对。对于固着的软体动物来说，应对盐度压力时唯一可行的行为选择就是“紧闭”，将其组织与环境隔离开来。虽然这种方式在短期内有效，但长期隔离会产生有害的生理后果，尤其是对于那些在与外部环境隔离的外套腔中孵化胚胎的雌性个体。在昆皮连河口，智利牡蛎（Ostrea chilensis）在其孵化季节中近三分之一的时间处于盐度低到足以导致雌性隔离的环境中。当雌性个体如此自我隔离时，其外套腔液中的溶解氧在10分钟内就降至缺氧水平。在孵化胚胎的雌性个体中，这种氧气消耗并不均匀：在触须区域（胚胎聚集的地方）氧气消耗比吸入区域更快。此外，当雌性个体孵化晚期胚胎时，触须区域的氧气减少得更快，晚期胚胎消耗氧气的速度明显比早期发育阶段的胚胎更快。最后，智利牡蛎利用无氧代谢来应对隔离引起的缺氧，因为乳酸在雌性个体（孵化的>未孵化的）和胚胎（晚期>早期）的组织中都有积累。我们的研究结果表明了一种适应性回避行为（紧闭）与这种行为带来的潜在有害后果（缺氧）之间的权衡。通过雌性个体有意识地抽水使胚胎在整个外套腔中循环，可防止它们在触须之间的区域聚集，从而避免在那里形成缺氧条件。此外，雌性个体及其胚胎的无氧代谢能力应有助于它们耐受在环境盐度长期降低期间外套腔与周围环境隔离时最终出现的低氧水平。
