Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, California, USA.
PLoS Genet. 2011 Aug;7(8):e1002204. doi: 10.1371/journal.pgen.1002204. Epub 2011 Aug 18.
A role for natural selection in reinforcing premating barriers is recognized, but selection for reinforcement of postmating barriers remains controversial. Organisms lacking evolvable premating barriers can theoretically reinforce postmating isolation, but only under restrictive conditions: parental investment in hybrid progeny must inhibit subsequent reproduction, and selected postmating barriers must restore parents' capacity to reproduce successfully. We show that reinforced postmating isolation markedly increases maternal fitness in the fungus Neurospora crassa, and we detect the evolutionary genetic signature of natural selection by quantitative trait locus (QTL) analysis of the reinforced barrier. Hybrid progeny of N. crassa and N. intermedia are highly inviable. Fertilization by local N. intermedia results in early abortion of hybrid fruitbodies, and we show that abortion is adaptive because only aborted maternal colonies remain fully receptive to future reproduction. In the first QTL analysis of postmating reinforcement in microbial eukaryotes, we identify 11 loci for abortive hybrid fruitbody development, including three major QTLs that together explain 30% of trait variance. One of the major QTLs and six QTLs of lesser effect are found on the mating-type determining chromosome of Neurospora. Several reinforcement QTLs are flanked by genetic markers showing either segregation distortion or non-random associations with alleles at other loci in a cross between N. crassa of different clades, suggesting that the loci also are associated with local effects on same-species reproduction. Statistical analysis of the allelic effects distribution for abortive hybrid fruitbody development indicates its evolution occurred under positive selection. Our results strongly support a role for natural selection in the evolution of reinforced postmating isolation in N. crassa.
自然选择在加强交配前障碍方面起着重要作用，但选择加强交配后障碍仍然存在争议。缺乏可进化的交配前障碍的生物理论上可以加强交配后隔离，但只有在限制条件下：杂交后代的父母投资必须抑制后续繁殖，并且选择的交配后障碍必须恢复父母成功繁殖的能力。我们表明，在真菌Neurospora crassa 中，强化交配后隔离显著增加了母体的适应性，并且我们通过对强化屏障的数量性状位点（QTL）分析检测到了自然选择的进化遗传特征。Neurospora crassa 和 N. intermedia 的杂交后代高度不育。由当地 N. intermedia 受精导致杂交果实体早期流产，我们表明流产是适应性的，因为只有流产的母菌落仍然完全接受未来的繁殖。在微生物真核生物中首次对交配后强化的 QTL 分析中，我们鉴定了 11 个导致杂交果实体发育失败的位点，包括三个主要的 QTL，它们共同解释了 30%的性状方差。三个主要 QTL 之一和六个较小效应的 QTL 位于 Neurospora 的交配型决定染色体上。几个强化 QTL 被遗传标记包围，这些标记要么在 Neurospora 不同进化枝的不同交配型之间的交叉中表现出遗传标记的分离扭曲，要么表现出与其他位点的等位基因的非随机关联，这表明这些位点也与同种繁殖的局部效应有关。对杂交果实体发育失败的等位基因效应分布的统计分析表明，其进化是在正选择作用下发生的。我们的结果强烈支持自然选择在 Neurospora crassa 中强化交配后隔离进化中的作用。
