Shiotsugu Jason, Leroi Armand M, Yashiro Hideko, Rose Michael R, Mueller Laurence D
Department of Ecology and Evolutionary Biology, University of California, Irvine, California, 92697.
Evolution. 1997 Feb;51(1):163-172. doi: 10.1111/j.1558-5646.1997.tb02397.x.
The relationship between the processes of density-dependent and age-specific selection has been investigated by examining a common phenotype, urea resistance, which has apparently evolved in response to each of these selection mechanisms. Twenty populations that have experienced differing levels of age-specific selection show differences in egg-to-adult viability in environments with high levels of urea. Among this group of populations, it appears that resistance to urea is correlated with longevity, but not development time. Ten populations kept at extreme larval densities for many generations also show responses to urea: those kept at high larval densities appear to be most resistant to urea. However, these populations show no differences in adult longevity. An additional five populations were selected directly for urea resistance by adding this compound to the larval food environment. Again, there was a strong response to this artificial selection, with urea resistance increasing dramatically, but these populations showed no response in adult longevity or resistance to crowding when compared to five control populations. There is clearly no simple relationship between longevity and larval urea resistance. It may be that age-specific and density-dependent selection induce similar changes in this phenotype, but do so through different genetic and physiological pathways. We suggest that these data are not consistent with the view of constant and symmetric genetic variance-covariance matrices. These data support a more prominent role for observations of evolutionary trajectories rather than static measurements of genetic components of variance.
通过研究一种常见的表型——尿素抗性，来探究密度依赖型选择和年龄特异性选择过程之间的关系。尿素抗性显然是针对这些选择机制中的每一种而进化出来的。在经历了不同程度年龄特异性选择的20个种群中，在高尿素环境下，卵到成虫的存活率存在差异。在这组种群中，对尿素的抗性似乎与寿命相关，但与发育时间无关。在极高幼虫密度下饲养了许多代的10个种群也表现出对尿素的反应：那些饲养在高幼虫密度下的种群似乎对尿素最具抗性。然而，这些种群在成虫寿命上没有差异。通过在幼虫食物环境中添加这种化合物，直接选择了另外5个种群以获得尿素抗性。同样，对这种人工选择有强烈反应，尿素抗性显著增加，但与5个对照种群相比，这些种群在成虫寿命或对拥挤的抗性方面没有反应。显然，寿命与幼虫尿素抗性之间不存在简单的关系。可能是年龄特异性选择和密度依赖型选择在这种表型上诱导了相似的变化，但通过不同的遗传和生理途径实现。我们认为这些数据与恒定且对称的遗传方差 - 协方差矩阵的观点不一致。这些数据支持进化轨迹观察比方差遗传成分的静态测量发挥更突出的作用。
