Deep sampling of Hawaiian Caenorhabditis elegans reveals high genetic diversity and admixture with global populations

Abstract

Hawaiian isolates of the nematode species <i>Caenorhabditis elegans</i> have long been known to harbor genetic diversity greater than the rest of the worldwide population, but this observation was supported by only a small number of wild strains. To better characterize the niche and genetic diversity of Hawaiian <i>C. elegans</i> and other <i>Caenorhabditis</i> species, we sampled different substrates and niches across the Hawaiian islands. We identified hundreds of new <i>Caenorhabditis</i> strains from known species and a new species, <i>Caenorhabditis oiwi</i>. Hawaiian <i>C. elegans</i> are found in cooler climates at high elevations but are not associated with any specific substrate, as compared to other <i>Caenorhabditis</i> species. Surprisingly, admixture analysis revealed evidence of shared ancestry between some Hawaiian and non-Hawaiian <i>C. elegans</i> strains. We suggest that the deep diversity we observed in Hawaii might represent patterns of ancestral genetic diversity in the <i>C. elegans</i> species before human influence.