In ectotherms, lower temperatures in high-latitude environments would theoretically reduce the annual growth rates of individuals. If slower growth and resultant smaller body size reduce fitness, individuals in higher latitudes may evolve compensatory responses. Two alternative models of such latitudinal compensation are possible: Model I: thermal reaction norms for growth rates of high-latitude individuals may be horizontally shifted to a lower range of temperatures, or Model II: reaction norms may be vertically shifted so that high-latitude individuals can grow faster across all temperatures. Model I is expected when annual growth rates in the wild are only a function of environmental temperatures, whereas Model II is expected when individuals in higher latitudes can only grow during a shorter period of a year. A variety of mixed strategies of these two models are also possible, and the magnitude of horizontal versus vertical variation in reaction norms among latitudinal populations will be indicative of the importance of "temperature" versus "seasonality" in the evolution of latitudinal compensation. However, the form of latitudinal compensation may be affected by possible genetic constraints due to the genetic architecture of reaction norms. In this study, we examine the inter- and intrapopulation variations in thermal reaction norms for growth rate of the medaka fish Oryzias latipes. Common-environment experiments revealed that average reaction norms differed primarily in elevation among latitudinal populations in a manner consistent with Model II (adaptation to "seasonality"), suggesting that natural selection in high latitudes prefers individuals that grow faster even within a shorter growing season to individuals that have longer growing seasons by growing at lower temperatures. However, intrapopulation variation in reaction norms was also vertical: some full-sibling families grew faster than others across all temperatures examined. This tendency in intrapopulation genetic variation for thermal reaction norms may have restricted the evolution of latitudinal compensation, irrespective of the underlying selection pressure.

译文

:在等温线中,高纬度环境中的低温理论上会降低个人的年增长率。如果较慢的生长和由此产生的较小的体型降低了适应性,则高纬度地区的人们可能会出现代偿性反应。这种纬度补偿的两个替代模型是可能的:模型I:高纬度个体生长速率的热反应规范可以水平移动到较低的温度范围,或者模型II:反应规范可以垂直移动以使高纬度个人可以在所有温度下更快地成长。当野外的年增长率仅是环境温度的函数时,可以预期为模型I,而当纬度较高的人只能在较短的一年内增长时,则可以预测为模型II。这两种模型的多种混合策略也是可能的,并且在纬度种群之间反应规范的水平相对于垂直变化的大小将指示“温度”相对于“季节性”在纬度补偿演变中的重要性。但是,由于反应规范的遗传结构,纬度补偿的形式可能会受到可能的遗传约束的影响。在这项研究中,我们研究了aka对印度med鱼Oryzias latipes生长速度的热反应规范中的种群间和种群内变化。共同环境实验表明,平均反应规范主要在纬度种群之间以与II型一致(适应“季节性”)的方式在海拔高度上有所不同,这表明高纬度地区的自然选择更倾向于即使在较短的生长季节中生长速度更快的个体也比生长在较低温度下的生长季节较长的个体。但是,种群内反应规范的变化也是垂直的:在所有考察的温度范围内,一些全兄弟家庭的生长速度快于其他家庭。无论潜在的选择压力如何,热反应范围内种群遗传变异的这种趋势都可能限制了纬度补偿的演变。

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