Ungerer M C, Baird S J, Pan J, Rieseberg L H
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Proc Natl Acad Sci U S A. 1998 Sep 29;95(20):11757-62. doi: 10.1073/pnas.95.20.11757.
Hybrid or "recombinational" speciation refers to the origin of a new homoploid species via hybridization between chromosomally or genetically divergent parental species. Theory predicts that this mode of speciation is punctuated, but there has been little empirical evidence to support this claim. Here, we test the hypothesis of rapid hybrid speciation by estimating the sizes of parental species chromosomal blocks in Helianthus anomalus, a wild sunflower species derived via hybridization between H. annuus and H. petiolaris. Analysis of the frequency spectrum of parental species chromosomal blocks with respect to predictions based on R. A. Fisher's [Fisher, R. A. (1953) Heredity 8, 187-197] junctions approach, suggests that H. anomalus arose rapidly, probably in fewer than 60 generations. This result is corroborated by independent lines of evidence demonstrating (i) a significant concordance between the genomes of H. anomalus and early generation H. annuus x H. petiolaris synthetic hybrids, and (ii) a rapid recovery of pollen fertility in these synthetic hybrid lineages. These results are not only consistent with theory but also provide a new and general method for estimating the tempo of hybrid speciation and dating the origin of hybrid zones.
杂交或“重组”物种形成是指通过染色体或基因不同的亲本物种之间的杂交产生新的同倍体物种。理论预测这种物种形成模式是间断性的，但几乎没有实证证据支持这一说法。在此，我们通过估计异常向日葵（Helianthus anomalus）中亲本物种染色体片段的大小来检验快速杂交物种形成的假设，异常向日葵是一种通过向日葵（H. annuus）和叶柄向日葵（H. petiolaris）杂交产生的野生向日葵物种。根据R. A. 费希尔（Fisher, R. A. (1953) Heredity 8, 187 - 197）的交汇方法，分析亲本物种染色体片段的频谱与预测结果，表明异常向日葵迅速形成，可能在不到60代的时间内。这一结果得到了独立证据的证实，这些证据表明：（i）异常向日葵的基因组与早期向日葵×叶柄向日葵合成杂种的基因组之间存在显著一致性；（ii）这些合成杂种谱系中花粉育性迅速恢复。这些结果不仅与理论一致，还提供了一种新的通用方法，用于估计杂交物种形成的速度并确定杂交区域的起源时间。
