Selfing is the safest sex forCaenorhabditis tropicalis

Abstract

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, C. 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 gene drive elements, genetically consistent with maternal toxin/zygotic antidote systems. Driver loci harbor novel and duplicated genes, and their activity is modified by mito-nuclear background. Segregating drivers dramatically reduce fitness, and simulations show that selfing limits their spread. Frequent selfing in C. tropicalis may therefore be a strategy to avoid drive-mediated outbreeding depression.

The parasitic nematode Strongyloides ratti exists as populations of long-lived asexual lineages

“…Specifically, analysis of worldwide populations of C. elegans find that genetic variation is concentrated in a number of genomic regions (56 and 19 kb mean and median size, respectively), with evidence suggesting that diversity in these regions is maintained by balancing selection (Lee et al, 2021). In the C. tropicalis genome, genetic variation is also distributed heterogeneously across its genome, for example with some 140 high genetic diversity classified regions extending for no more than 30 kb (Noble et al, 2021). While there is a superficial similarity between the patterns of genomically concentrated genetic diversity in two Caenorhabditis species and in S. ratti, the mechanisms generating these patterns might be different.…”