Estimating Mortality Risks Associated with Starvation for Atlantic Cod Larvae using Molecular Markers and Cox Regression Models

在实验室饲养实验的基础上，本研究重点展示了利用分子标记与统计模型相结合来估计大西洋鳕鱼幼虫饥饿死亡率的可行性。我们早期的研究已经确定，大体积RNA、18S核糖体RNA （rRNA）和金属硫蛋白（MT） mRNA水平可能是鳕鱼幼虫饥饿的特异性标志物。为了进一步表征18s rRNA和MT对大西洋鳕鱼摄食、发育和生长变化的响应，我们将完成一系列的实验室实验。实验室结果（分子生物学和生存数据）将用于校准Cox回归模型，以估计大西洋鳕鱼幼虫的饥饿死亡风险。本研究选择的非比例风险Cox回归模型是寿险行业通常用于建立风险和保险费率的模型。它可以适应时间相关的协变量，时间滞后效应，以及在所研究的生物体的生命周期中危险率的逐步变化。我们早期的研究表明，rRNA水平的显著下降可以作为大西洋鳕鱼幼虫饥饿初期的标志。MT mRNA水平的急剧增加也被证明是饥饿的指示。这两种标记都将用于确定重新进食后从饥饿中恢复的情况。如果能够建立从饥饿中恢复的能力，死亡率风险估计的能力将大大增强。单独的一个标记可能无法有足够的信心定义饥饿时的“不归点”。动物和人体研究表明，缺乏饮食会导致多聚体分解，核糖体的数量和活性降低。饥饿后再进食导致rnas水平显著增加。然而，当饥饿超过了“不返回点”，即rRNA水平在重新进食后未能反弹时，死亡率就开始了。在某种程度上，大西洋鳕鱼是其他鱼类和无脊椎动物产生浮游生物幼虫的合适模型，这项工作将提供幼虫对变化的摄食条件的分子反应的图片，并提供确定生长，饥饿死亡率和摄食条件的工具。这些研究应能深入了解环境变化对鱼类生产的影响。

Based on laboratory feeding experiments, this effort focuses on demonstrating the feasibility of using molecular markers coupled with statistical modeling for estimation of starvation-induced mortality in larval Atlantic cod. Our earlier studies have established that bulk RNA, 18S ribosomal RNA (rRNA) and metallothionein (MT) mRNA levels may serve as specific markers for starvation in cod larvae. A series of laboratory experiments will be completed to further characterize the responses of 18s rRNA and MT to changes in feeding, development and growth in Atlantic cod. Laboratory results (molecular biology and survival data) will be used to calibrate a Cox regression model for estimation of starvation mortality risks in larval Atlantic cod. The nonproportional hazards Cox regression model chosen for this study is commonly used by the life insurance industry for establishing risks and premium rates. It can accommodate time-dependent covariates, time-lagged effect, and a stepwise change in hazard rates over the lifespan of the organism studied. Our earlier work established that significant decreases18s rRNA levels can be used as a marker for the initial stages of starvation in Atlantic cod larvae. Dramatic increases in MT mRNA levels also were shown to be indicative of starvation. Both markers will be used to pinpoint recovery from starvation after refeeding. The power of mortality risks estimation will greatly increase if recovery from starvation can be established. A single marker alone may not be able to define the `point-of-no-return` in starvation with sufficient confidence. Animal and human studies have shown that dietary deprivation leads to polysome breakdown and a reduction in the number and activity of ribosomes. Refeeding after starvation results in significant increase in the levels of rRNAs. However, when starvation has exceeded the `point-of-no-return`, i.e. rRNA levels fail to rebound after refeeding, mortality sets in. To the extent that Atlantic cod is a suitable model for other fish and invertebrates that produce planktonic larvae, this effort will provide a picture of the molecular response of larvae to changing feeding conditions and provide tools to determine growth, starvation mortality and feeding conditions. These studies should provide insight into the effects of environmental variability on production of fish.