Damos Petros, Soulopoulou Polyxeni
Department of Crop Production, Faculty of Agriculture, Forestry and Natural Environment, Aristotle University of Thessaloniki, Thessaloniki, Greece.
Department of Environment, University of the Aegean, Mytilene, Lesvos, Greece.
PLoS One. 2015 Aug 28;10(8):e0127328. doi: 10.1371/journal.pone.0127328. eCollection 2015.
Temperature implies contrasting biological causes of demographic aging in poikilotherms. In this work, we used the reliability theory to describe the consistency of mortality with age in moth populations and to show that differentiation in hazard rates is related to extrinsic environmental causes such as temperature. Moreover, experiments that manipulate extrinsic mortality were used to distinguish temperature-related death rates and the pertinence of the Weibull aging model. The Newton-Raphson optimization method was applied to calculate parameters for small samples of ages at death by estimating the maximum likelihoods surfaces using scored gradient vectors and the Hessian matrix. The study reveals for the first time that the Weibull function is able to describe contrasting biological causes of demographic aging for moth populations maintained at different temperature regimes. We demonstrate that at favourable conditions the insect death rate accelerates as age advances, in contrast to the extreme temperatures in which each individual drifts toward death in a linear fashion and has a constant chance of passing away. Moreover, slope of hazard rates shifts towards a constant initial rate which is a pattern demonstrated by systems which are not wearing out (e.g. non-aging) since the failure, or death, is a random event independent of time. This finding may appear surprising, because, traditionally, it was mostly thought as rule that in aging population force of mortality increases exponentially until all individuals have died. Moreover, in relation to other studies, we have not observed any typical decelerating aging patterns at late life (mortality leveling-off), but rather, accelerated hazard rates at optimum temperatures and a stabilized increase at the extremes.In most cases, the increase in aging-related mortality was simulated reasonably well according to the Weibull survivorship model that is applied. Moreover, semi log- probability hazard rate model illustrations and maximum likelihoods may be usefully in defining periods of mortality leveling off and provide clear evidence that environmental variability may affect parameter estimates and insect population failure rate. From a reliability theory standpoint, failure rates vary according to a linear function of age at the extremes indicating that the life system (i.e., population) is able to eliminate earlier failure and/or to keep later failure rates constant. The applied model was able to identify the major correlates of extended longevity and to suggest new ideas for using demographic concepts in both basic and applied population biology and aging.
温度意味着变温动物种群衰老存在不同的生物学原因。在这项研究中，我们运用可靠性理论来描述蛾类种群死亡率与年龄的一致性，并表明危险率的差异与温度等外在环境因素有关。此外，通过操纵外在死亡率的实验来区分与温度相关的死亡率以及威布尔衰老模型的适用性。应用牛顿 - 拉夫森优化方法，通过使用评分梯度向量和海森矩阵估计最大似然曲面，来计算小样本死亡年龄的参数。该研究首次揭示，威布尔函数能够描述处于不同温度条件下蛾类种群衰老的不同生物学原因。我们证明，在适宜条件下，昆虫死亡率随年龄增长而加速，这与极端温度下每个个体以线性方式逐渐死亡且死亡概率恒定的情况相反。此外，危险率的斜率转向一个恒定的初始率，这是未出现损耗（如无衰老）的系统所呈现的模式，因为失败或死亡是一个与时间无关的随机事件。这一发现可能令人惊讶，因为传统上大多认为，在衰老种群中，死亡率会呈指数增长直至所有个体死亡。而且，与其他研究相比，我们未观察到任何典型的晚年减速衰老模式（死亡率趋于平稳），而是在最适宜温度下危险率加速上升，在极端温度下稳定上升。在大多数情况下，根据所应用的威布尔生存模型，与衰老相关的死亡率增加得到了合理模拟。此外，半对数概率危险率模型图示和最大似然估计在确定死亡率趋于平稳的时期可能很有用，并提供明确证据表明环境变异性可能影响参数估计和昆虫种群故障率。从可靠性理论的角度来看，在极端情况下，故障率随年龄呈线性函数变化，这表明生命系统（即种群）能够消除早期故障和/或使后期故障率保持恒定。所应用的模型能够识别延长寿命的主要相关因素，并为在基础和应用种群生物学及衰老研究中运用人口统计学概念提出新的思路。
