Gene conversion restores selfing in experimentally evolving C. elegans populations with fog-2 loss-of-function mutation

We have discovered a new case of gene conversion restoring ability of self-fertilization in obligatory outcrossing Caenorhabditis elegans populations. The fog-2(q71) mutation, used to transform the nematodes’ mating system from mostly self-fertilization to obligatory outcrossing, was spontaneously removed by replacing a fragment of fog-2 gene with a fragment of its paralog, ftr-1 . This has occurred spontaneously in experimental evolution with large populations, evolving with fog-2(q71) mutation for over a hundred generations, without addition mutagens or other factors promoting mutation accumulation. A converted fog-2 allele restoring hermaphrodite sperm production was detected in five experimental populations. This raises the question about stability of obligatory outcrossing populations in long-term experiments.