A newborn F-box gene blocks gene flow by selectively degrading phosphoglucomutase in species hybrids.

The establishment of reproductive barriers such as postzygotic ybrid ncompatibility (HI) remains the key to speciation. Gene duplication followed by differential functionalization has long been proposed as a major model underlying HI, but little supporting evidence exists. Here, we demonstrate that a newborn F-box gene, , of the nematode specifically inactivates an essential phosphoglucomutase encoded by in its sister species and their hybrids. Zygotic expression of specifically depletes SHLS-1, but not SHLS-1, in approximately 40 min starting from gastrulation, causing embryonic death. is one of thirty-three paralogues emerging from a recent surge in F-box gene duplication events within , all of which are evolving under positive selection. undergoes turnover even among populations. Differential expansion of F-box genes between the two species could reflect their distinctive innate immune responses. Collectively, we demonstrate how recent duplication of genes involved in protein degradation can cause incidental destruction of targets in hybrids that leads to HI, providing an invaluable insight into mechanisms of speciation.