Bierbaum Todd J, Mueller Laurence D, Ayala Francisco J
Departments of Zoology and Entomology, Michigan State University, East Lansing, MI, 48824.
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, 92717.
Evolution. 1989 Mar;43(2):382-392. doi: 10.1111/j.1558-5646.1989.tb04234.x.
Populations of Drosophila melanogaster were maintained for 36 generations in r- and K-selected environments in order to test the life-history predictions of theories on density-dependent selection. In the r-selection environment, populations were reduced to low densities by density-independent adult mortality, whereas populations in the K-selection environment were maintained at their carrying capacity. Some of the experimental results support the predictions or r- and K-selection theory; relative to the r-selected populations, the K-selected populations evolved an increased larval-to-adult viability, larger body size, and longer development time at high larval densities. Mueller and Ayala (1981) found that K-selected populations also have a higher rate of population growth at high densities. Other predictions of the thoery are contradicted by the lack of differences between the r and K populations in adult longevity and fecundity and a slower rate of development for r-selected individuals at low densities. The differences between selected populations in larval survivorship, larval-to-adult development time, and adult body size are strongly dependent on larval density, and there is a significant interaction between populations and larval density for each trait. This manifests an inadequacy of the theory on r- and K-selection, which does not take into account such interactions between genotypes and environments. We describe mechanisms that may explain the evolution of preadult life-history traits in our experiment and discuss the need for changes in theories of density-dependent selection.
为了检验密度依赖选择理论的生活史预测，黑腹果蝇种群在r选择和K选择环境中维持了36代。在r选择环境中，种群因与密度无关的成虫死亡率而降至低密度，而K选择环境中的种群则维持在其承载能力水平。一些实验结果支持了r选择和K选择理论的预测；相对于r选择的种群，K选择的种群在高幼虫密度下进化出了更高的幼虫到成虫的存活率、更大的体型和更长的发育时间。穆勒和阿亚拉（1981）发现，K选择的种群在高密度下也有更高的种群增长率。该理论的其他预测与r种群和K种群在成虫寿命和繁殖力方面缺乏差异以及r选择个体在低密度下发育速度较慢相矛盾。所选种群在幼虫存活率、幼虫到成虫的发育时间和成虫体型方面的差异强烈依赖于幼虫密度，并且每个性状在种群和幼虫密度之间存在显著的相互作用。这表明r选择和K选择理论存在不足，该理论没有考虑到基因型与环境之间的这种相互作用。我们描述了可能解释我们实验中幼虫前期生活史性状进化的机制，并讨论了改变密度依赖选择理论的必要性。
