Weis Arthur E, Abrahamson Warren G, Andersen Mark C
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, 92717, USA.
Department of Biology, Bucknell University, Lewisburg, PA, 17837, USA.
Evolution. 1992 Dec;46(6):1674-1697. doi: 10.1111/j.1558-5646.1992.tb01161.x.
Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in phenotypic selection. The intensity of selection imposed by parasitoids and predators on gallmaking larvae, for gall size, was measured across 16 populations over the course of 4 generations, for a total of 64 population-generations. Directional selection was quantified by i, the selection intensity, and variance selection by j', a measure of the intensity of selection on phenotypic variance. Size-dependent attack by parasitoids caused upward directional selection (mean i = 0.42; SE = 0.023), while size-dependent bird attack favored larvae that induced smaller galls (mean i = -0.07; SE = 0.013. The mean net directional selection intensity was 0.35 (SE = 0.030), which indicates that insects inducing larger galls are generally favored by selection. The opposing patterns of size-dependent attack resulted in stabilizing selection in half the population generations, with an overall average. j' of -0.11 (SE = 0.078). The magnitude of directional selection was strongly influenced by the population mean gall size and weakly by the optimal gall size. The intensity of variance selection was strongly influenced by the shape of the fitness function, with sigmoidal and Gaussian-like shapes causing greater depletion of phenotypic variance.
环境条件的自然波动很可能会引起自然选择强度或方向的变化。为了探究表型选择的变化模式，对一种昆虫——菊方翅实蝇（Eurosta solidaginins Fitch，双翅目；实蝇科）进行了一项长期研究，这种昆虫会在多年生草本植物高茎一枝黄花（Solidago altissima，菊科）上诱导形成茎瘿。在4代的时间里，对16个种群中寄生蜂和捕食者对造瘿幼虫的瘿大小的选择强度进行了测量，总共涉及64个种群世代。定向选择通过选择强度i进行量化，方差选择通过j'进行量化，j'是对表型方差选择强度的一种度量。寄生蜂对大小依赖的攻击导致向上的定向选择（平均i = 0.42；标准误 = 0.023），而鸟类对大小依赖的攻击则有利于诱导较小瘿的幼虫（平均i = -0.07；标准误 = 0.013）。平均净定向选择强度为0.35（标准误 = 0.030），这表明诱导较大瘿的昆虫通常受到选择的青睐。大小依赖攻击的相反模式在一半的种群世代中导致了稳定选择，总体平均j'为 -0.11（标准误 = 0.078）。定向选择的幅度受种群平均瘿大小的强烈影响，受最优瘿大小的影响较弱。方差选择的强度受适合度函数形状的强烈影响，S形和类高斯形会导致表型方差的更大消耗。
