Countergradient Variation: Adaptation to Seasonality in Fishes

最近在鱼类中发现生长能力（即最大生长潜力）与生长季节长度在纬度梯度上呈反比关系。这种有趣的种内“反梯度变异”形式可能代表了一种应对季节性环境的广泛适应策略。本项目主要以大西洋银鱼Menidia Menidia作为模式生物，评估其纬度适应的选择力、进化反应和生理机制。其前提是，北方的快速生长是对强烈季节性环境的进化反应：也就是说，在北方，体型大是为了度过漫长的冬天，但只有一个短暂的生长季节才能达到体型大。关于更快的生长只会以牺牲其他一些生命史功能为代价的理论预测也将得到检验。以不同纬度的银鱼为实验饵料，进行了以下试验：1)确定体型、脂质储存和基因型对银鱼越冬存活率的影响；2)测试能量获取和分配给各种代谢功能（如食物加工、生长、游泳和生殖性能）的遗传变异。研究结果将对我们在生命史理论、资源管理和海洋生物对气候变化的反应方面的知识产生影响。

An inverse relation between the capacity for growth (i.e. maximum growth potential) and length of the growing season over a latitudinal gradient has recently been discovered in fishes. This intriguing form of intraspecific "countergradient variation" may represent a widespread adaptive strategy for coping with seasonal environments. Using primarily the Atlantic silverside, Menidia menidia, as a model organism, this project will evaluate the selective forces, evolutionary responses, and physiological mechanisms underlying latitudinal adaptation. The premise is that rapid growth in the north is an evolutionary response to an intensely seasonal environment: i.e., one where large size is necessary to survive long winters, but where only a brief growing season is available in which to attain large size. The theoretical prediction that faster growth can occur only at the expense of some other life history function will also be tested. Experiments on laboratory stocks of silversides from different latitudes are designed to: 1) determine the influence of body size, lipid storage and genotype on overwinter survival; and 2) test for genetic variation in energy acquisition and allocation to various metabolic functions such as food processing, growth, swimming and reproductive performance. Results will have implications for our knowledge of life history theory, resource management, and the response of marine organisms to climate change.