Genomic sequence and structural variations accumulating between laboratory lineages of wild type C. elegans

Laboratory cultivation subjects model organisms to selective pressure and genetic drift that can result in the accumulation of many genomic and phenotypic differences over time. The nematode Caenorhabditis elegans has been used for research since the 1970s, and studies comparing the N2 Bristol and CB4856 Hawaiian isolates provided foundational knowledge about metazoan genome evolution. Most comparative genomics studies have used these isolates because their long-term geographical isolation promoted a high degree of genomic divergence within the species. Further, there is growing evidence of phenotypic differences between laboratory lineages of each wild type isolate after repeated independent lab cultivation of these strains. To examine the genomic divergence between different laboratory lineages the Bristol and Hawaiian backgrounds, we first generated de novo genome assemblies of two Bristol and two Hawaiian lineages from Illumina and PacBio sequencing reads. Following genome assembly, we quantified Single Nucleotide Polymorphisms (SNPs), short insertion/deletions (indels), and genomic structural variants (SVs). Between laboratory lineages of the Bristol isolate, we identified 25,432 SNPs, 5,202 indels, and 441 SVs. When aligning laboratory lineages of the Hawaiian isolate, we identified 4,518 SNPs, 1,188 indels, and 387 SVs. For both sets of comparisons, we find that SNPs and indels are broadly enriched in introns and depleted from coding sequences. In contrast to SNPs and indels, we find that genomic SVs are enriched in intergenic sequences. Taken together, our analyses reveal the accumulation of genomic divergence between lineages of Bristol and Hawaiian C. elegans from independent lab cultivation, and how these variants may underpin emergent phenotypic differences observed in the two most popularly used C. elegans wild type isolates.