Elife. 2021 Jan 11;10:e62587. doi: 10.7554/eLife.62587.
Luke M Noble 1 2, John Yuen 1, Lewis Stevens 3, Nicolas Moya 3, Riaad Persaud 1, Marc Moscatelli 1, Jacqueline L Jackson 1, Gaotian Zhang 3, Rojin Chitrakar 4, L Ryan Baugh 4, Christian Braendle 5, Erik C Andersen 3, Hannah S Seidel 6, Matthew V Rockman 1
1 Department of Biology and Center for Genomics & Systems Biology, New York University, New York, United States.
2 Institute de Biologie, École Normale Supérieure, CNRS, Inserm, Paris, France.
3 Department of Molecular Biosciences, Northwestern University, Evanston, United States.
4 Department of Biology, Duke University, Durham, United States.
5 Institut de Biologie Valrose, Université Côte d’Azur, CNRS, Inserm, Nice, France.
6 Department of Biology, Eastern Michigan University, Ypsilanti, United States.
Mating systems have profound effects on genetic diversity and compatibility. The convergent evolution of self-fertilization in three Caenorhabditis species provides a powerful lens to examine causes and consequences of mating system transitions. Among the selfers, Caenorhabditis tropicalis is the least genetically diverse and most afflicted by outbreeding depression. We generated a chromosomal-scale genome for C. tropicalis and surveyed global diversity. Population structure is very strong, and islands of extreme divergence punctuate a genomic background that is highly homogeneous around the globe. Outbreeding depression in the laboratory is caused largely by multiple Medea-like elements, genetically consistent with maternal toxin/zygotic antidote systems. Loci with Medea activity harbor novel and duplicated genes, and their activity is modified by mito-nuclear background. Segregating Medea elements dramatically reduce fitness, and simulations show that selfing limits their spread. Frequent selfing in C. tropicalis may therefore be a strategy to avoid Medea-mediated outbreeding depression.