Lynch Michael, Pfrender Michael, Spitze Ken, Lehman Niles, Hicks Justin, Allen Deborah, Latta Leigh, Ottene Marcos, Bogue Farris, Colbourne John
Department of Biology, University of Oregon, Eugene, Oregon, 97403.
Department of Biology, University of Miami, Coral Gables, Florida, 33124.
Evolution. 1999 Feb;53(1):100-110. doi: 10.1111/j.1558-5646.1999.tb05336.x.
In an effort to elucidate the evolutionary mechanisms that determine the genetic architecture of a species, we have analyzed 17 populations of the microcrustacean Daphnia pulex for levels of genetic variation at the level of life-history characters and molecular markers in the nuclear and mitochondrial genomes. This species is highly subdivided, with approximately 30% of the variation for nuclear molecular markers and 50% of the variation for mitochondrial markers being distributed among populations. The average level of genetic subdivision for quantitative traits is essentially the same as that for nuclear markers, which superficially suggests that the life-history characters are diverging at the neutral rate. However, the existence of a strong correlation between the levels of population subdivision and broadsense heritabilities of individual traits argues against this interpretation, suggesting instead that the among-population divergence of some quantitative traits (most notably body size) is being driven by local adaptation to different environments. The fact that the mean phenotypes of the individual populations are also strongly correlated with local levels of homozygosity indicates that variation in local inbreeding plays a role in population differentiation. Rather than being a passive consequence of local founder effects, levels of homozygosity may be selected for directly for their effects on the phenotype (adaptive inbreeding depression). There is no relationship between the levels of variation within populations for molecular markers and quantitative characters, and this is explained by the fact that the average standing genetic variation for life-history characters in this species is equivalent to only 33 generations of variation generated by mutation.
为了阐明决定物种遗传结构的进化机制，我们分析了17个微型甲壳动物水蚤（Daphnia pulex）种群在生活史特征以及核基因组和线粒体基因组分子标记水平上的遗传变异水平。该物种高度细分，核分子标记约30%的变异以及线粒体标记约50%的变异分布在种群之间。数量性状的遗传细分平均水平与核标记基本相同，表面上这表明生活史特征以中性速率分化。然而，种群细分水平与个体性状广义遗传力之间存在强相关性，这与该解释相悖，反而表明一些数量性状（最显著的是体型）的种群间差异是由对不同环境的局部适应驱动的。各个种群的平均表型也与局部纯合度水平密切相关，这一事实表明局部近亲繁殖的差异在种群分化中起作用。纯合度水平可能并非局部奠基者效应的被动结果，而是因其对表型的影响而被直接选择（适应性近亲繁殖衰退）。分子标记和数量性状在种群内的变异水平之间没有关系，这可以用该物种生活史特征的平均现存遗传变异仅相当于由突变产生的33代变异这一事实来解释。
