Fry J D, Heinsohn S L, Mackay T F
Department of Genetics, North Carolina State University, Raleigh 27695-7614, USA.
Genetics. 1998 Mar;148(3):1171-88. doi: 10.1093/genetics/148.3.1171.
If genetic variation for fitness traits in natural populations ("standing" variation) is maintained by recurrent mutation, then quantitative-genetic properties of standing variation should resemble those of newly arisen mutations. One well-known property of standing variation for fitness traits is inbreeding depression, with its converse of heterosis or hybrid vigor. We measured heterosis for three fitness traits, pre-adult viability, female fecundity, and male fertility, among a set of inbred Drosophilia melanogaster lines recently derived from the wild, and also among a set of lines that had been allowed to accumulate spontaneous mutations for over 200 generations. The inbred lines but not the mutation-accumulation (MA) lines showed heterosis for pre-adult viability. Both sets of lines showed heterosis for female fecundity, but heterosis for male fertility was weak or absent. Crosses among a subset of the MA lines showed that they were strongly differentiated for male fertility, with the differences inherited in autosomal fashion; the absence of heterosis for male fertility among the MA lines was therefore not caused by an absence of mutations affecting this trait. Crosses among the inbred lines also gave some, albeit equivocal, evidence for male fertility variation. The contrast between the results for female fecundity and those for male fertility suggests that mutations affecting different fitness traits may differ in their average dominance properties, and that such differences may be reflected in properties of standing variation. The strong differentiation among the MA lines in male fertility further suggests that mutations affecting this trait occur at a high rate.
如果自然种群中适合度性状的遗传变异（“现存”变异）是由反复突变维持的，那么现存变异的数量遗传特性应该类似于新出现突变的特性。适合度性状现存变异的一个众所周知的特性是近亲繁殖衰退，与之相反的是杂种优势或杂交活力。我们测量了一组最近从野外获得的近交黑腹果蝇品系以及一组已被允许积累自发突变超过200代的品系中，三个适合度性状（成虫前期存活率、雌蝇繁殖力和雄蝇生育力）的杂种优势。近交品系在成虫前期存活率上表现出杂种优势，但突变积累（MA）品系没有。两组品系在雌蝇繁殖力上都表现出杂种优势，但雄蝇生育力的杂种优势较弱或不存在。MA品系的一个子集之间的杂交表明，它们在雄蝇生育力上有强烈分化，这些差异以常染色体方式遗传；因此，MA品系中雄蝇生育力不存在杂种优势不是因为缺乏影响该性状的突变。近交品系之间的杂交也给出了一些关于雄蝇生育力变异的证据，尽管不太明确。雌蝇繁殖力和雄蝇生育力结果之间的对比表明，影响不同适合度性状的突变在其平均显性特性上可能存在差异，并且这种差异可能反映在现存变异的特性中。MA品系在雄蝇生育力上的强烈分化进一步表明，影响该性状的突变发生率很高。
