Mitton J B, Koehn R K
Genetics. 1975 Jan;79(1):97-111. doi: 10.1093/genetics/79.1.97.
Populations of Fundulus heteroclitus, (Cyprinodontidae) a widespread coastal marine fish, were studied in control and artificially heated environments on the North Shore of Long Island, New York to determine (1) patterns of variation in biochemical phenotypes and (2) the extent to which this variation reflected adaptation to environmental characteristics. Variation at three of twelve polymorphic isoenzyme loci from the warm water population was beyond the range of variation among control populations, and resembled those determined for populations living at more southern latitudes. Hence, these differences were interpreted as adaptations to warm environments. Significant differences in allele frequencies and zygotic proportions at ten of twelve isoenzyme loci were found associated with differences in environments, sexes, and/or age classes. These data strongly support the view that protein polymorphisms are adaptive. Several observations suggested that selection acts upon multilocus phenotypes rather than upon those of single loci. Several di-locus phenotypic distributions were demonstrated to be nonrandom, and those that exhibited similar patterns of dependence over years were postulated to be maintained by selection. Highly heterozygous fish exhibited superior viability when cohorts were compared over successive years. The consequences of the polygynous mating system in this species for maintaining genetic variation and for allowing rapid evolutionary response to a variable environment are discussed.
底鳉（Fundulus heteroclitus，属于鲤齿科）是一种广泛分布的沿海海洋鱼类，在纽约长岛北岸的对照环境和人工加热环境中对其种群进行了研究，以确定：（1）生化表型的变异模式；（2）这种变异反映对环境特征适应的程度。来自温水种群的十二个多态同工酶位点中的三个位点的变异超出了对照种群间的变异范围，并且与生活在更南纬度地区的种群所确定的变异相似。因此，这些差异被解释为对温暖环境的适应。在十二个同工酶位点中的十个位点上，发现等位基因频率和合子比例的显著差异与环境、性别和/或年龄组的差异相关。这些数据有力地支持了蛋白质多态性具有适应性的观点。一些观察结果表明，选择作用于多位点表型而非单一位点表型。几个双位点表型分布被证明是非随机的，并且那些多年来表现出相似依赖模式的分布被假定是由选择维持的。当连续多年比较同群个体时，高度杂合的鱼类表现出更强的生存能力。讨论了该物种一夫多妻制交配系统对于维持遗传变异以及允许对多变环境做出快速进化反应的后果。
