Stevens, Lewis, Buchanan, Claire, Andersen, Erik, Stinson, Loraina, Dilks, Clayton, Tanny, Robyn, Lu, Dan, Zhang, Gaotian, Evans, Kathryn, Zdraljevic, Stefan, Crombie, Tim, Lee, Daehan, Roberto, Nicole, Wang, Ye, Cook, Daniel
[
International Worm Meeting,
2021]
Caenorhabditis elegans isolated from the Hawaiian Islands are known to harbor a high degree of genetic diversity relative to non-Hawaiian isolates. It was recently suggested that Hawaiian C. elegans can be partitioned into at least four genetically distinct groups. An analysis of geospatial environmental data further suggested that the genetic groups might associate with environmental parameters such as elevation and temperature, although the sample size for that study was small (n = 43 isolates). To better characterize the niche and genetic diversity of Hawaiian C. elegans and further define the associations of genetic groups with environmental parameters, we sampled different substrates and niches across the Hawaiian Islands six times over a three-year period. In total, we isolated 7,107 nematodes from 2,400 of 4,506 substrate samples (53% success rate). Among the nematodes we isolated, we identified five Caenorhabditis species, including 499 C. elegans, 377 C. briggsae, and 55 C. tropicalis isolates. We measured several environmental parameters at each sampling site and combined them with environmental parameters from geospatial databases to reveal that C. elegans is typically found in cooler and relatively drier climates at higher elevation than the other two selfing Caenorhabditis species. We isolated C. elegans most frequently from montane-alpine mesic forest habitat dominated by plant species native to the Hawaiian Islands. When possible, we cryopreserved C. elegans isolates and sequenced their genomes. To date, including Hawaiian isolates from collaborators, we have sequenced the genomes of 505 Hawaiian C. elegans isolates. With these data, we grouped the isolates into 163 isotypes (strains belonging to a single isotype have >0.9997 genome-wide concordance). We found that some of the isotypes were collected from the same locations over the three-year sampling period, and most of the collections of the same isotype were found within 500 meters of each other. Principal component analysis (PCA) of genetic variation revealed that the 163 isotypes fall into seven genetically distinct groups, three more than previously found on the islands with a smaller sample. Taken together, our findings begin to outline the spatiotemporal patterns of C. elegans genetic diversity on the Hawaiian Islands and raise new questions about evolutionary forces driving the genetic structure we have uncovered. For example, are these groups isolated by ecological or geographic distances, or perhaps both, and to what extent do reproductive incompatibilities contribute to the structure we have observed?